-
1Silicon-Based Reducing Agents
Gerald L. LarsonVice President, Research & Development
Materials for the reduction
of:AldehydesKetonesAcetalsKetalsEsters
LactonesThioestersEnamines
IminesAcids
AmidesHalidesOle ns
Metal Halides
Supplement to the Gelest Catalog, Silicon, Germanium & Tin
Compounds, Metal Alkoxides and Metal Diketonates which is available
on request.
127
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
Gerald L. LarsonVice President, Research & Development
-
2SILICON-BASED REDUCING AGENTS
Introduction The widely used organometallic-based reducing
agents can be broadly classi ed as either ionic, such as lithium
aluminum hydride and sodium borohydride, or free-radical such as
tri-n-butyltin hydride. The mechanistic differences between these
two classes of reducing agents very often complement one another in
their ability to reduce organic substrates. Organosilanes have been
found to possess the ability to serve as both ionic and
free-radical reducing agents. These reagents and their reaction
by-products are safer and more easily handled and disposed of than
other reagents. Their reductive abilitiesare accomplished by
changes in the nature of the groups attached to silicon, which can
modify the character of the Si-H bond in the silane. For example,
the combination of a triethylsilane and an acid has proven to be
excellent for the reduction of substrates that can generate a
stable carbenium ion intermediate. Examples of substrates that fall
into this class are ole ns, alcohols, esters, lactones, aldehydes,
ketones, acetals, ketals, and other like materials. On the other
hand triphenylsilane andespecially tris(trimethylsilyl)silane have
proven to be free-radical reducing agents that can substitute for
tri-n-butyltin hydride.The reductions with silanes can take place
with acid catalysis in which the silane provides the hydride to a
carbenium ion intermediate. This is often the situation in the
reduction of carbonyls, ketals, acetals and similar species.
Additionally, the silane reductions can also be carried out with
uoride ion catalysis to generate a silane with more hydridic
character.
Some of the key reductions possible with silanes are summarized
in Table 1.
128
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
3General Considerations Hydridosilanes are readily produced on
an industrial scale through the use of Grignard chemistry starting
with trichlorosilane, methyldichlorosilane, and
dimethylchlorosilane, among others, as key raw materials.
Alternatively, the Si-X (X = primarily Cl or OR) bond can be
reduced to Si-H.
The organosilanes are basically hydrocarbon-like in that they
are stable to water, are, in general, ammable and are lipophilic.
In contrast to hydrocarbons, the low molecular weight silanes such
as monosilane, methylsilane, and dichlorosilaneare pyrophoric. The
silanes will react with base or, more slowly, with acid to give the
corresponding siloxane with the evolutionof hydrogen gas. They show
a strong, characteristic, carbonyl-like absorption in the infrared
at about 2200 cm-1.1
The metallic nature of silicon and its low electronegativity
relative to hydrogen - 1.8 versus 2.1 on the Pauling scale - lead
to polarization of the Si-H bond such that the hydrogen is hydridic
in nature. This provides an ionic, hydridic reducingagent that is
milder than the usual aluminum-, boron-, and other metal-based
hydrides. Thus, triethylsilane, among others, has been used to
provide the hydride in Lewis acid-catalyzed reductions of various
carbenium ion precursors. In addition, the Si-H bond can be
employed in various radical reductions wherein the silane provides
the hydrogen radical.
Table 2 shows the Si-H bond strengths for several silanes. From
these data the rather wide variation in the Si-H bond strengths
from tris(trimethylsilyl)silane on the low-energy end to tri
uorosilane on the high-energy end can be noted. This is yet another
example of the extraordinary effect that groups attached to silicon
can have on the chemistry of the silane and that these effects can
go beyond the simple steric effects that have been so successfully
applied with the silicon-based blockingagents.2-4
TABLE 2 BOND STRENGTHS OF VARIOUS HYDRIDOSILANES
Compound Product Code Bond Strength ReferencekJ mol-1 kcal
mol-1
F3Si-H SIT8373.0 419 100 5
Et3Si-H SIT8330.0 398 95 6
Me3Si-H SIT8570.0 398 95 7
H3Si-H SIS6950.0 384 92 6
Cl3Si-H SIT8155.0 382 91 5
PhMeHSi-H SIP6742.0 382 91 6
Me3SiSiMe
2-H not offered 378 90 6
PhH2Si-H SIP6750.0 377 90 6
(MeS)3Si-H not offered 366 87 6
H3SiSiH
2-H SID4594.0 361 86 5
(Me3Si)
3Si-H SIT8724.0 351 84 6
Although triethylsilane has been the most popular of the
silicon-based reducing agents, in principal any Si-H-containing
system can provide the hydride for many or most of these
reductions. Considerations would include availability, economics,
and silicon-containing by-products. The silicon-containing
by-products are usually the silanol or disiloxane in the case of
the trisubstituted silanes, or silicones in the case of the di- or
monosubstituted silane reducing agents. Such considerations can
result in greater ease of handling and puri cation of the nal
product.
Silicon-based reductions have been reviewed, though never in a
comprehensive manner.6,8-13 A comprehensive review has been
accepted for publication.14
129
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
4Silicon-Based Radical Reductions Griller and Chatgilialoglu6
realized that the low bond energy of the Si-H bond in
tris(trimethylsilyl)silane compared well with that of the Sn-H bond
in tri-n-butyltin hydride (322 kJmol-1; 77 kcal mol-1), and that
this reagent should, therefore, be a viable alternative for radical
reductions and one that would avoid the potential problems of
working with toxictin materials and trace tin-containing impurities
in the nal product. This proved to be the case, and a number of
radical reductions with tris(trimethylsilyl)silane have been
reported and reviewed.15,16 Included among these are the reductions
of organic halides, 17-19 esters,20 xanthates, selenides, sul des,
thioethers, and isonitriles.21
As an example of a free radical reduction, the diphenylsilane
reduction of thioesters to ethers has been recently reported.22
This reaction uses the catalytic triphenyltin hydride as the actual
reducing agent.
O
S
O
1) Ph2SiH2Ph3SnH cat.Et3B/rt/1h
60%2) AIBN/85-100 C
Ionic Reductions with Silanes General Considerations As pointed
out above the silanes provide a mild form of the hydride and as
such can be useful in various hydridic reductions. The general and,
admittedly simpli ed, view of such reductions can be visualized as
shown below where a carbenium ion is reduced by a silane. In this
scenario, the carbenium ion receives the hydride from the silane,
and the silanetakes on the leaving group from the carbon
center.
R3C-X + R3Si-H R3C-H + R3Si-X
It has been shown that in the gas phase the reaction shown below
is exothermic by approximately 8 kcal/mol indicating that the
trimethylsilicenium ion is, at least in the gas phase, more stable
than the tert-butyl carbenium ion.23
Although the existence of free silicenium ions do not exist in
solution under normal, unbiased conditions, it can be assumed that
the silicon center is free to take on considerable positive charge
in its reactions. Reductions based on this premise includethose of
ole ns, ketones, aldehydes, esters, organic halides, acid
chlorides, acetals, ketals, alcohols as well as metal salts.
(CH3)3C + + (CH3)3Si-H (CH3)3C-H + (CH3)3Si +
Silane Reduction of Alcohols to Alkanes The general equation for
the silane reduction of alcohols to alkanes is illustrated below.
The reaction proceeds best when the alcohol can lead to a
stabilized carbenium ion. Thus, secondary and tertiary aliphatic
alcohols and benzylic alcohols are readily reduced. Trialkyl
substituted silanes are more reactive than dialkylsilanes and di-
or triarylsilanes. Typicaland highly effective conditions for these
reductions are treatment of the alcohol with the silane and tri
uoroacetic acid in dichloromethane. Triethylsilane is often the
silane of choice due to its ease of handling and high
reactivity.23,24
R3C-OH + R3Si-H R3C-H + R3Si-OH and/or R3Si-O-SiR3Acid
catalyst
The reduction of secondary alcohols with a silane and a protic
acid does not occur. These reductions require the use of a strong
Lewis acid such as boron tri uoride or aluminum chloride.25,26
130
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
5 Primary aliphatic alcohols are not reduced with silanes.27
Benzylic alcohols, on the other hand, are reduced under rather mild
conditions to the corresponding toluene derivative.28
tBu
tBu
tBu
OH
CH2Cl2/TFA
tBu
tBu
tBuMe
R3Si-H
The selective reduction of a benzylic alcohol in the presence of
benzyl ethers, a tetrahydrofuran and an acetal has been
reported.29
OBnO
OBn
OEt
MeO
HOEt3Si-H/TFA
CH2Cl2/ rt
OBnO
OBn
OEt
MeO76%
Primary alcohols can be reduced to the alkane when the reaction
is catalyzed by the very strong Lews acid, tris(penta
uorophenyl)borane. The reaction requires two equivalents of the
silane as the rst equivalent serves to silylate the alcohol. It is
believed that the silylated alcohol is nucleophilically displaced
in these transformations.30 On the other hand, with boron tri
uoride etherate as the catalyst, the benzylic alcohol can be
reduced in the presence of a primary or secondary alcohol.31,32
E t3S iH , B (C 6F 5) 3
C H 2C l2, rt, 20 hPh OH Ph
95%
O H
O H
Ph
Ph O HPh
Ph
E t3S iH , C H 2C l2
E t2O B F 3, 0o, 0.5 h
90%
O
O
N
OM e
M eO
H
H
O H
H O
M e
E t3S iH , C H C l3
E t2O B F 3O
O
N
O M e
M eO
H
H
H O
M e92%
The reduction of an allylic alcohol in the presence of a
tertiary alcohol is possible.33
H OOH
E t3S iH , L iC lO 4
E t2O, rt, 16 h
O H
52%
131
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
6Silane Reduction of Alkyl Halides As with the reduction of
alcohols to alkanes, the acid-catalyzed reduction of alkyl halides
to alkanes requires the formation of a relatively stable carbenium
ion intermediate that can accept the hydride from the silane. Thus,
tertiary, secondary, allylic and benzylic halides lend themselves
to this type of reduction. Under certain conditions primary halides
canbe reduced, but carbenium ion rearrangements are a
problem.34,35
Br
Et3SiD
AlCl3
D
+
E t3S iH , A lC l3
H C l
39% 26%
B r
Cl Et3SiHAlCl3
H
57%
Trialkylsilanes, being better hydride donors, provide less
rearranged product in these reductions than their dialkyl or
monoalkyl counterparts.35
The reduction of organic halides with pentacoordinate
hydridosilanes has been reported.36
Tertiary alkyl uorides can be reduced to the alkane in excellent
yield.37 -Chloro ethyl ethers are cleanly reduced to the alkane.38
An allyl chloride was reduced in the presence of an allylic
tosylate.39
OPh
F
O
OPh
O
E t3S iH , B F 3 OE t2
C H 2C l2, 20o, 8 h
100%
OO
C l OO
E t3S iH , PdC l2
rt, 10 min
95%
S O 2T ol
C l
S O 2T olPh2S iH 2, Z nC l2, Pd(PPh3)4
T H F , rt, 12 h, 50 , 6 h
58%
132
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
7 The reduction of -halo ketones and -halo esters has been
reported to occur with the combinations of PhSiH
3/Mo(CO)
6,40 Ph
2SiH
2/ZnCl
2/(PPh
3)
4Pd,40 and Et
3SiH/PdCl
238 with the rst of these proving to be the best.
2-Bromopropiophenone was reduced to propiophenone with
polymethylhydrogensiloxane, PMHS, without reduction of the
carbonyl.41
Br
O O
PMHS, Pd(PPh3)4, Bn3N
MeCN/Me2SO (1:1), 110o, 3 h
80%
The tetramethyldisiloxane reduction of an aryl chloride in the
presence of a benzophenone moiety was carried out in high yield.42
The high-yield reduction of an aryl tri ate has been
reported.43
O
C l
H M e2S iOS iM e2H , 10% N i/C
PPh3, dioxane, reflux, 15 h
O
96%
N
N C F 3
C F 3
OT fn-C 10H 21N
N C F 3
C F 3
n-C 10H 21E t3S iH , Pd(OA c)2
dppp, D M F , 60 , 3 d
95%
Silane Reduction of Alkynes The reduction of p-tolylacetylene
with triethylsilane gave p-ethyltoluene although in low
yield.44
E t3S iH , T F A
rt, 120 hH
21%
Most of the alkyne reductions have been carried out on suitable
enynes, diynes, or bromo acetylene derivatives to produce cyclic
products.45-47
T B S OO T M S
PM H S , Pd2(bpa)3 C H C l3, (o-tol)3P
H OA c, C lC H 2C H 2C l, rtT B S O
O T M S
90%
B r
O E t3S iH , Pd(PPh3)4
C s2C O 3, D M F , 80 , 3 h
O
48%
133
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
8Silane Reduction of Aromatics Furans are reduced to
tetrahydrofurans with triethylsilane under suitable catalysis.48
Thiophenes can be similarly reduced.49
O O
E t3S iH , T F A , F 3B OE t2
20o, 4 min
70%
SO
OE t3S iH , T F A , 55 , 15 h
SOS iE t3
O
45%
Anthracene was reduced to 9,10-dihydroanthracene in good yield
with triethylsilane and boron tri uoride hydrate.50
The partial reduction of other polyaromatics was reported.50
E t3S iH , F 3B OH 2
C H 2C l2, 25o, 1 h
89%
The pyridine ring of quinoline was reduced in preference to the
benzene ring. The isolated product was the N-silylated derivative.
Some of the dihydroreduction product was also observed.51,52
N
PhM eS iH 2, C p2T iM e2
80o, 8 hN
S iPhM eH
N
S iPhM eH
56% 18%
+
Silane Reduction of Ethers Trityl ethers are readily removed as
triphenylmethane with triethylsilane and triethylsilyltri ate as
the catalyst.53
B zO O
B zO
OB zO
O T r
E t3S iH , E t3S iOT f
C H 2C l2, rt, 5 min
87%
+ Ph3C HO
H O
H O
O T r
O T rB zO O
B zO
OB zO
O H
O
H O
H O
O H
OH
Under the in uence of the strong Lewis acid, tris(penta
uorophenyl)borane, dialkyl ethers were cleaved in high yield.54
A tertiarybutylcyclopropenyl ether was reduced to give the
cyclopropene.55
n-C 16H 33O
C 16H 33-nE t3S iH , B (C 6F 5)3
C H 2C l2, rt, 20 hn-C 16H 34 + n-C 16H 33O S iE t3
98% 98%
Ph
Ph
Ph
O B u-t
E t3SiH, TFAPh
Ph
Ph
H45%
134
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
9Silane Reduction of Carboxylic Acids Ethyldimethylsilane and a
ruthenium catalyst were used to reduce aliphatic carboxylic acids
to the corresponding alcohol.56 With tris(penta uorophenyl)borane
as catalyst, triethylsilane reduces carboxylic acids to the
alkane.57,58
O H
O
OHE tM e2S iH , catalyst
1,4-dioxane, 20 , 0.5 h
72%
R uR u(C O)2(O C )2R u
O(C O)2
C O 2H E t3S iH , B (C 6F 5)3
C H 2C l2, rt, 20 h
94%
Silane Reduction of Esters and Lactones The reduction of esters
and lactones has proven to be possible with the isolation of the
corresponding alcohol, ether, hemiacetal, or monosilyl acetal.
Thus, an ester was reduced to the alcohol in good yield in the
presence of an epoxide.59 A methyl ester was selectively reduced to
the alcohol in the presence of a tert-butyl ester.60 A
butyrolactone was reduced to the tetrahydrofuran,56 as well as to a
hemiacetal.56,61,62
O
H
O E t
OO
H
O H
PM H S , C p2T iC l2, n-B uL i
T H F , rt, 1 h
91%
M eO OB u-t
O O
H O OB u-t
O
87%
PM H S , C p2T iC l2, n-B uL i
T H F , 78o, 1 h
O
O O
O
B nOO
O O
OH
B nO
PM H S , C p2T i(OC 6H 4-C l-p)2
T B A F /A lumina, M eC 6H 5, rt
91%
Both an intermolecular63 and an intramolecular version of the
conversion of an ester to a silyl acetal have been
reported.64,65
O M e
O
O M e
OS iE t3
E t3S iH , E tI , E t2N H , [R uC l2(C O) 3]2
M eC 6H 5, 100 , 16 h
92%
S iM es2H
T B A F , 0
OM es2S i
O E t
dr = 98:2
OO
OO
E t E t E t E t
C O 2E t
91%
135
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
10
The reduction of ,-unsaturated esters can occur with
1,4-adddition to provide the silyl ketene acetal or the -silyl
ester.66 The intermediate silyl ketene acetal can be trapped with a
suitable electrophile either in an intermolecular or intramolecular
fashion.67,68
O E t
O
O E t
OS iE t3E t3S iH , C lR h(PPh3)3
C 6H 6, 80 , 2 h
74%
+ O E t
O S iE t3
6%
OE t
O
O E t
O
O E t
O S iE t3
E t3S i E t3S i+
E t3S iH , C lR h(PPh3)3
C 6H 6, 70 , 3 h
52% 28%
O
OO
+ M e3S iH , R hC l3 3H 2O, 25 O
OM e3S iO
34%
E t3S iH , R hH (PPh3)4
M ePh, 50 , 16 hH
O
C O 2Pr-i
OS iE t3
C O 2Pr-i
O S iE t3
C O 2Pr-i+
20% 40%
Silane Reduction of Aldehydes The acid-catalyzed reduction of
aldehydes with silanes works best in the presence of water.69 In
addition esters can be formed when an organic acid is the catalyst
employed.70
H
O Et3SiH
TFAO OH O2CCF3+ +
nC7H15CHOEt3SiH (n-C7H15)2O + n-C7H15-OH
66% 34%F3BOEt2
PhCHOEt3SiH
TFA
Et3SiH
H2O/H2SO4
PhCH2-O-CH2Ph
PhCH2OH
80%
98%sulfolane
An excellent alternative for the reduction of aldehydes to
alcohols is through the use of triethylsilane with uncomplexed
boron tri uoride in dichloromethane.71 This method gives the
corresponding alcohol in high yield and very short reaction times.
An extremely high-yield reductive conversion of aldehydes to
unsymmetrical ethers involves the reaction of the aldehyde with a
trimethylsilyl ether in the presence of a silane and a strong Lewis
acid, with trimethylsilyl tri ate being especially ef cient.72 Such
silicon-based reductive-condensation chemistry should be applicable
to combinatorial chemistry where product isolation is a crucial
issue.
n-C4H9CHO + n-C6H13OSiMe3Et3SiH/Me3SiI
CH2Cl2/0 C/2hn-C5H11-O-C6H13-n
100%
136
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
11
Aromatic aldehydes can be fully reduced to the corresponding
toluene derivative.71,73
OCH3
CHOEt3SiH/BF3
CH2Cl2/0 C/10 min
OCH3
CH3
OCH3
CHOEt3SiH/TFA
rt/45 min83%100%
The conversion of aromatic aldehydes to benzylic halides has
also been shown.74-76 The best reducing agent for this seems to be
tetramethyldisiloxane.
Cl
CHO
Cl
CH2I
(HMe2Si)2O/Me3SiCl
NaI/CH3CN/0 C/5 min
95%
Under catalysis by uoride ion aldehydes are reduced to the
corresponding silyl ether of the alcohol. Hydrolysis of the silyl
ethers provides the unprotected alcohols. Cesium uoride has been
shown to be an excellent promoter for these conversions,77,78 as
have tetra-n-butyl ammonium uoride (TBAF) and
tris(diethylamino)sulfonium di uorotrimethylsilicate (TASF).79 This
can also be used as a route to trimethylsilyl-protected alcohols
from aldehydes.
2 n-C6H12CHOPh2SiH2
CsF(n-C7H15O)2SiPh2
The reduction of aldehydes to alcohols has also been carried out
with polylmethylhydrogensiloxane (PMHS) as the hydride source. In
this case, the work-up includes reaction with methanol to release
the free alcohol.80
The selective reduction of aldehydes over ketones can be
realized with polymethylhydrogensiloxane as the reducing agent with
uoride ion-catalysis.81
PhH
O
Ph nBu
O+
PMHS
TBAF
Ph
Ph nBu
OH+
OH 87%
< 8%
The reductive amidation of aldehydes proved possible via the
acid-catalyzed triethylsilane reduction in the presence of a
nitrile or a primary amide.82,83
PhC H O + C H 3C N PhC H 2N H C O M eaq. H 2S O 4
E t3S iH80%
H O 2C
C H O
H O 2C
NH
Ph
O
E t3S iH , T F A , PhC ON H 2
M eC 6H 5, 120o, 18 h
96%
137
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
12
The reduction of ,-unsaturated aldehydes can occur in a 1,2- or
1,4-fashion.84
C H O O HPh2S iH 2, (Ph3P)3R hC l
0o, 1 h
97%
C H O C H OE t3S iH , (Ph3P)3R hC l
rt, 1 h
97%
Silane Reduction of Ketones Silanes have been used for the
reduction of ketones to alcohols with excellent results.85 The
reduction of ketones or aldehydes in the presence of acetonitrile
and an acid provides an alkyl acetamide.82 The comparable reduction
of aldehydes to alkyl acetamides is also possible.82
O
HO H
H
Et3SiH
TFA
HO H
H
OH
: ratio = 1:4
O
Et3SiH/CH3CN
75% aq. H2SO4/rt/65h NHCOMe
In a similar manner, the reduction of ketones and aldehydes to
esters has been reported.82 This reaction is always accompanied
with the formation of the symmetrical ether.
O
Et3SiH/TFArt/1.5h
H O2CCF3
+ O2
75% 25%
Et3SiH/HCOOHrt/8h
CHO O2CH O+
The reduction of aryl ketones (acetophenone derivatives) to the
methylene is readily accomplished.86 Triethylsilane with titanium
tetrachloride works best for this transformation, though other
systems also work well.
Ar R
O
AcidAr R
R3SiH
138
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
13
The selective reduction of aryl ketones to alcohols over dialkyl
ketones can be carried out with phenyldimethylsilane in the
presence of cuprous chloride or cuprous acetate.87
Cyclic ethers can be formed in the reduction of diketones or
hydroxyketones.88-90 Epoxy ketones can lead to ethers as
well.91
O O
1. M e3S iH , T M S OT f, C H 2C l2
0 , 4 h then rt, 2 h
2. H 2O
O
H O
O
O
M e3S iH , T M S OT f
C H 2C l2, 0 , 4 h, then rt, 2 h
O O+
42% 42%
S
OO HO
: OS
O:E t3S iH , T M S OT f
C H 2C l2, 0 , 15 min
97%
O O
Ph3S iH , catalyst, C H 2C l2
78 , 6 h; 0 , 12 h OH HOH81%
The reductive halogenation of ketones has been shown. Thus,
acetophenone derivatives are converted to benzylic halides.92,93 An
ynone was converted to the propargyl chloride in good yield.92
C l
B r
C l
C l
B r
O
M e2C lS iH , I n(OH )3
C H C l3, rt, 4 h
99%
O I
T M D S , I 2, C H 2C l2
5o, 5 min
76%
O C l
M e2C lS iH , In(OH )3
C H C l3, 0o, 0.3 h
78%
The reduction of aliphatic ketones to the methylene is best
accomplished with the tris(penta uorophenyl)borane catalyst.94
O
PM H S , B (C 6F 5)3, C H 2C l2
rt, 5 - 20 min
90%
139
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
14
Dimethyl(diethylamino)silane served as the reducing agent and
the amine source in the reductive amination of acetophenone.95
O N E t2E t2N S iH M e2, T iC l4
C H 2C l2, 0o to rt, 36 h
65%
The reduction of ,-unsaturated ketones can occur in a 1,2- or
1,4-fashion.84
O O O H
+E t2S iH 2, (Ph3)3R hC l
0 , 30 min
3% 97%
O O OH
+E t3S iH , (Ph3)3R hC l
80 , 25 h
90% 6%
Some selectivity was seen in the reduction of an enone in the
presence of a ketal96 and an acid, allyl alcohol, and halide.97
Ph2S iH 2, Z nC l2
Pd(PPh3) 4, rt, 1 hO
O
O
O
O
O95%
O
C l C F 3H O
H O 2CO
C l C F 3H O
H O 2CE t3S iH , T F A , 0o, 1 h
rt, 48 h
82%
Silane Reduction of Other Carbonyl Systems The reduction of
amides to the amine has been shown to occur in high yields
employing triethylsilane or diphenylsilane.98,99
N
O
NE t3S iH , R e(C O) 10, E t2N H
M eC 6H 5, 100
96%
The one-pot reduction of amides to aldehydes with diphenylsilane
has been reported.99 This provides a potentially highly-useful,
non-oxidative entry into aldehydes.
N CN Pr-i2
O
10N C
H
O
10
Ph2S iH 2, T i(OPr-i)4, 20
80%
NMe2
OTBSO
Ph2SiH2 (1.1 eq)
Ti(OPr-i)4 (1 eq)87%
H
OTBSO
140
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
15
The reduction of acids and esters to alcohols with
polymethylhydrogensiloxane occurs in good yields in the presence of
titanium tetraisopropoxide100 or tetrabutylammonium uoride.101 The
reduction of esters has also been carried out with diphenylsilane
and rhodium catalysis.102
OEt
O
OBnPMHS
Ti(OiPr)4/THF OHOBn
89%
OMe
O
8 OH8PMHS
TBAF95%
The triethoxysilane reduction of esters to alcohols in high
yields is possible.103 This transformation also takes place with
PMHS as the reducing agent.104,105
COOEt (EtO)3SiH/Ti(OiPr)440 - 50 C OH
The conversion of lactones to lactols was accomplished via a
titanium-catalyzed reduction with PMHS.106
O
O
Cp2Ti(OC6H4Cl)2TBAF/Al2O3
PMHS/toluene
O
OH
94%
The reduction of imines to amines with trichlorosilane and
dichlorosilane was reported. Dichlorosilane gave the best
results.107
S
OMe
N
S
OMeHN
Silane
Cl2SiH2
Cl3SiH
90%
61%
F3BOEt2
The reduction of oximes to alkoxyamines is accomplished with
phenyldimethylsilane and tri uoroacetic acid.108
NR2
R1 OR3 PhMe2SiH
TFANH
R2
R1 OR3
141
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
16
Silane Reduction of Acetals, Ketals and Aminals The silane
reduction of acetals and ketals occurs readily in the presence of a
variety of silanes and acid catalysts. Both arylalkyl and dialkyl
ketals can be reduced to the methylene group.107
Ph
OO
1. E t3S iH , S nB r2-A cB r,
C H 2C l2, rt, 24 h
2. n-B u3SnH , A I B N ,
C 6H 6, reflux, 0.5 h
Ph77%
M eO O M e
Ph Ph
1. E t3S iH , S nB r2-A cB r,
C H 2C l2, rt, 24 h
2. n-B u3S nH , A I B N ,
C 6H 6, reflux, 0.5 h
67%
The reduction of the acetal of benzaldehyde was carried out in
good yield in the presence of an alkyl azide.109 The reduction of a
peroxymethyl ketal occurred to give triethylmethoxysilane and keep
the peroxide group as well as a primary alkyliodide.110 In another
similar example the peroxide functionality was lost.110
N 3
OO
PhH
PM H S , A lC l3, E t2O, C H 2C l2
rt, 12 h
69%7
N 3
B nOH O
7
OOM eO
OOH
E t3S iH , H OT f
II
H H56%
OO
OE t3S iH , H OT f
O
51%
Aminals and hemiaminals are reduced to amines.111
N-Trimethylsilyloxymethylimines can be reduced to the corresponding
imine.112 Related reactions are also possible.113,114
NN
H OM e
C O 2M e
E t3S iH , T F A
rt, 4 hN
N
HM e
C O 2M e
79%
M eO
NH
OH
O
E t3S iH , T F A
C H C l3, rt, 1- 4 h
M eO
N H M e
O
91%
O
NM eO 2C
OH
E t3S iH , T F A
C H C l3, rt, 20 h
O
NM eO 2C
M e63%
O
N OF moc NM e
OF moc
OH
E t3S iH , T F A
C H C l3, rt, 22 h
98%
142
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
17
Silane Reduction of Enamines and Enamides The organosilane
reduction of enamines has been reported.116 The reduction of
enamides can be carried out selectively in the presence of
enones.117,118
NH
M eO
M eO
E t3S iH , T F A
50 , 64 h
N
N Ph
HN
O
NH
M eO
M eO
N
N Ph
HN
O
58%
N
C O 2M e
C l
O
E t3S iH , T F A , C H 2C l2
0 , 6 h then rt, 6 hN
C O 2M e
C l
O
56%
N
O
O
OE t3S iH , T F A , C H C l3
20 , 24 h
N
O
O
O
75%
Silane Reduction of Ole ns Not surprisingly the ionic reduction
of suitable ole ns, i.e. those which can generate a relatively
stable carbenium ion, can be carried out by silanes in the presence
of an acid catalyst. The ability to generate the carbenium ion is
essential to thesuccess of the reaction. For example,
1-methylcyclohexene is readily reduced to methylcyclohexane whereas
cyclohexene itself is not reduced under the same and even more
forcing conditions.118 The most common set of conditions for these
reductions is an excess of tri uoroacetic acid, a strong acid with
a conjugate base of low nucleophilicity, and triethylsilane.119-123
Likewise, terminal ole ns that are not styrenic in nature and
1,2-disubstituted ole ns are not reduced with silanes, again, due
to the inability to form a suitable carbenium ion intermediate. On
the other hand, the reduction of enol ethers and similar ole ns
which can form good carbenium ions is possible.122,124
+2 Et3SiH/TFA
+
70% 100%
The reduction of ,-unsaturated carbonyls to their saturated
counterparts is conveniently carried out with silanes in the
presence of a rhodium or copper catalyst.125,126
OnC12H25
O
PhMe2SiH
CuCl/DMIOnC12H25
O95%
O
conditions
[Ph3PCuH]6 5 mol %
O
Bu3SnH; 40 min 80%
PhSiH3; 8 min 86%
143
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
18
Ojima and Kogure84 have shown that the reduction of
,-unsaturated ketones or aldehydes with triethylsilane or
ethyldimethylsilane gives 1,4-addition resulting in reduction of
the double bond whereas diphenylsilane gives 1,2-addition and
straight reduction of the carbonyl.
O
silane
(Ph3P)3RhCl
OH
+
O
EtMe2SiHPh2SiH2
2%99%
98%1%
An example of the reduction of a styrenic double bond in the
presence of another double bond and a ketone is shown below.127 The
double bond of an ,-unsaturated ketone was reduced with the
triethylsilane/acid combination, though regeneration of the ketones
was necessary.128
O
H
Et3SiH
TFA/CH2Cl2
O
H
H
1) Et3SiHTFA/CH2Cl2
O
OH
O
O2) NaOH/H2O3) [O]
The reduction of a trisubstituted ole n in the presence of an
ester was shown.129
O2CCH3 O2CCH3
Et3SiH/TFA
iPrNO2/LiClO490%
The silane reduction of acetylenes to alkanes is not a practical
approach to this transformation.130 The reduction of
vinylcyclopropane gave ethylcyclopropane in quantitative yield.131
Vinyl ethers are reduced to the corresponding alkyl ether.132
E t3S iH
T F A , 25o
100%
E t3SiH
T F AO O
80%
144
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
19
Stereoselective Silane-Based Reductions Doyle and West133
demonstrated that the acid-catalyzed reduction of alkyl-substituted
cyclohexanones with di-tert-butylsilane, di-tert-butylmethylsilane
and tri-tert-butylsilane proceeds with predominant formation of the
less stable isomer asthe tri uoroacetate. For example,
4-tert-butylcyclohexanone gives 67% of the
cis-4-tert-butylcyclohexyl tri uoroacetate.
OtBu2MeSiH/CF3CO2H
O2CCF3
OEt3SiH OSiEt3CF3CO2H
The reduction of 4-tert-butylcyclohexanone with triethylsilane
or dimethylphenylsilane preferentially gives the trans product.
Very high trans to cis stereoselectivity of this transformation
with triethoxysilane and TBAF was reported as was thereduction of
3-phenyl-2-butanone to anti 3-phenyl-2-butanol.134
The stereoselective silane reduction of -hydroxy ketones with
diisopropylchlorosilane has been demonstrated.135-137
OH O iPr2ClSiH
Et3N
O OSi-H
iPriPr
1) SnCl42) HF/H2O
OH OH
67% de >98%
The highly diastereoselective reduction of oximes has been
reported.108 The diastereoselectivity was much higher than that
reported for the corresponding reduction with lithium aluminum
hydride in diethyl ether.
Ph OAcN
BnOPhMe2SiH
TFA PhOAc
NHBnO
Ph OAcNH
BnO+
73%99 1
Ph OAcN PhMe2SiH
TFA PhOAc
NHBnO
Ph OAcNH
BnO
+77%
% %
OBn
82 18
The Lewis acid-catalyzed triphenylsilane reduction of hemiketals
was shown to occur with high stereoselectivity.140
OPhS
S
PhOH
PhMe2SiH/TiCl4
OPhS
S
PhH
cis:trans = 82:1
CH2Cl2/5 min
145
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
20
Asymmetric silane reductions A very ef cient asymmetric
reduction of arylalkyl ketones has been shown. The reaction, which
does not work well for prochiral dialkyl ketones, is carried out
with PMHS in the presence of a chiral titanium catalyst.138
O
"Ti"/C6H6
PMHS
OH
73% yield; 73% ee
A number of asymmetric, silane-based reductions have been
reported. In many cases these result in very high
enantioselectivity and offer an alternative to the asymmetric
hydrogenation protocol. Enones have been reduced in a 1,2-fashion,
as well as in a 1,4-manner, with high ee values.141,142
1. PhSiH3, (EBTHI)Ti, MeOH,
60, pyrrolidine, MeOH, THF
2. PMHS, ketone, MeOH, 15, 4 h
O OH
90%; 84% ee
O
Ph
O
Ph
PMHS, Ph3PCuH, DTBM-SEGPHOS
MeC6H5, 35, 16 h
95%; 99.5% ee
The intermediate enol silyl ether from the reduction of an enone
can be trapped with benzyl bromide.143
O
O
Bn
Ph2SiH2, CuCl, NaOBu-t
(S)-p-Tol-BINAP, MeC6H5, 0, 2 - 3 hPh
Ph
OSiPh2H
Ph95% ee
BnBr, TBAT
CH2Cl2/MeC6H5, rt
69%; dr = 94:6
146
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
21
The DTBM-SEGPHOS-catalyzed PMHS reduction of ,-unsaturated
esters provides the saturated ester in high enantiomeric
excess.144
OEt
Ph
O
OEt
Ph
O
HPMHS, (Ph3P)CuH
t-BuOH, MeC6H5, 0
92%; 98% ee
O
O
Ph
O
O
H
Ph
PMHS, (Ph3P)CuH
t-BuOH, MeC6H5, 0
96%; 99% ee
Buchwald and coworkers139 have reported the reduction of imines
in very high enantiomeric excess through the use of a titanium
catalyst activated with phenylsilane and the reduction with
polymethylhydrogen siloxane or phenylsilane. The asymmetric
reduction of imines has been reported in very high enantiomeric
excesses.139,145-147
NActivated Ti cat.
PMHS or PhSiH3slow addition of 3 amine
HN
95% 98% ee
NPhSiH3, catalyst
i-BuNH2, 65, 2.5 h
Cl
OMe
HN
Cl
OMe
E : Z = 15:1 92%, 99% ee
Reductions With Other Group 14 Hydrides The tri-n-butyltin
hydride reductions are well-known and have been reviewed.148 A
recent report shows that tri-n-butyltin hydride can provide the
hydrogen for the reductive amination of ketones and aldehydes, thus
providing an alternative to sodium cyanoborohydride for this
transformation.149 This same transformation was reported using
polymethylhydrogen siloxane, PMHS, as the reducing agent.150
R1 R2
O+ R2NH2+ ClO4-
Bu3SnH
DMF R1 R2
NR2
Triphenylgermane has been shown to reduce acid chlorides to
aldehydes with palladium(0) catalysis.151
R Cl
O Ph3GeHPd(PPh3)4
HMPA/80-100 C
R H
O
Tri-n-butylgermane has been employed in the reductive alkylation
of active ole ns, in particular acrylonitrile.152
CN+ R-I
Bu3GeH
AIBN/80 C/8hR
CN + R-H
54 - 79 % 3 - 14 %
147
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
22
TRI-SUBSTITUTED SILANE REDUCING AGENTSTABLE 3REDUCING AGENT
STRUCTURE COMMENTS
SIT8330.0TRIETHYLSILANE[617-86-7]TSCA
SiC2H5 H
C2H5
C2H5
Used to reduce metal salts.153 Enhances deprotection of
t-butoxycarbonyl-protected amines and tert-butylesters.154
Used in the reductive amidation of oxazolidinones with amino
acids to provide dipeptides.155 Converts aldehydes to symmetrical
and unsymmetrical ethers. 156 Used in the in-situ preparation of
diborane and haloboranes.157
SIT8570.0TRIMETHYLSILANE[993-07-7]TSCA
SiHCH3
CH3CH3
Potential reducing agent that will produce low boiling
hexamethyldisiloxane by-product.
SIT8385.0TRIISOPROPYLSILANE[6485-79-6]
SiCH
H3C CH3
HCH3C
H3C CHH3C CH3
H
Very sterically-hindered silane. Used as a cation scavenger in
the deprotection of peptides.158
SIT8665.0TRIPHENYLSILANE[789-25-3]TSCA
Si H
More effective radical-based reagent for reduction of organic
halides than the trialkylsilanes.156 Compares well with
tri-n-butyltin hydride in reduction of enones to ketones.63 Shows
good selectivity in the reduction of cyclic hemiacetals.77 Converts
O-acetyl furanoses and pyranoses to deoxy sugars.159
SIT8709.0TRI-n-PROPYLSILANE[998-29-8]TSCA
SiCH2CH2CH3
CH2CH2CH3
H CH2CH2CH3
Reactivity similar to that of triethylsilane.
SIT8376.0TRI-n-HEXYLSILANE[2929-52-4]TSCA
SiCH3(CH2)5 H(CH2)5CH3
(CH2)5CH3
Reactivity similar to that of triethylsilane but has higher
boiling point and produces a higher boiling by-product.
SIT8185.0TRIETHOXYSILANE[998-30-1] Si
OC2H5H
OC2H5
OC2H5
Reduces esters in the presence of zinc hydride catalyst.52
Reduces aldehydes and ketones to alcohols via the silyl ethers
in presence of fluoride ion.160 Gives 1,2-reduction of enones to
allyl alcohols.161
SIT8721.0TRIS(TRIMETHYLSILOXY)SILANE[1873-89-8]
SiHOSi(CH3)3
O Si(CH3)3OSi(CH3)3
Gives highly stereoselective reduction of substituted
cyclohexanones.51
148
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
23
SIT8724.0TRIS(TRIMETHYLSILYL)SILANE[1873-77-4] Si
Si(CH3)3
Si(CH3)3Si(CH3)3H
Undergoes exothermic decomposition at >100 C.Radical-based
reducing agent for organic halides, selenides, xanthates and
isocyanides and ketones in high yields.20 Can provide complementary
stereoselectivity to tri-n-butyltin hydride in the reduction of gem
dihalides.162 Mild reducing agent in nucleoside chemistry.163
SID3258.0DI-tert-BUTYLMETHYLSILANE[56310-20-4]
H3CCCH3
H3C Si
CH3C
CH3H3C
H
CH3
Used in reductive trifluoroacetolysis of ketones. Reacts faster
than di-tert-butylsilane.72
SID3410.0DIETHYLMETHYLSILANE[760-32-7]TSCA
CH3CH2Si
H
CH3CH3CH2
Similar to triethylsilane with lower boiling point.
SID3535.0DIISOPROPYLCHLOROSILANE[2227-29-4]TSCA
SiCH
CH
H3C CH3
CH3H3C
ClH
Used in a silylation-reduction-allylation sequence of -hydroxy
esters to homoallylic-substituted 1,3-diols.164Used in the
silylation-hydrosilation-oxidation of allyl alcohols to
1,3-diols.165 Reaction carried out in diastereoselective manner.
Reduces -hydroxy ketones to anti-1,3 diols. 166
SID4070.0DIMETHYLCHLOROSILANE[1066-35-9]TSCA
SiHCH3
CH3
Cl
Will form high-boiling polymeric by-products with aqueous
work-up.
SID4125.0DIMETHYLETHOXYSILANE[14857-34-2]TSCA
SiHCH3
CH3
OC2H5
Will form high-boiling polymeric by-products with aqueous
work-up.
SID4555.0DIPHENYLMETHYLSILANE[776-76-1]TSCA
SiCH3
H
Used to reduce -alkoxy ketones to diols and -aminoketones to
aminoethanols with high stereoselectivity.167
SIE4894.0ETHYLDIMETHYLSILANE[758-21-4]TSCA
SiCH3CH2 CH3
CH3H Similar to triethylsilane with lower boiling point.
SIE4890.0ETHYLDICHLOROSILANE[1789-58-8]TSCA
SiCH3CH2 Cl
ClH Will form high-boiling polymeric by-products with aqueous
work-up.
149
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
24
SiH3C
H
Cl
Cl
SiH3C
H
OC2H5
OC2H5
CH3(CH2)16CH2 SiCH3
CH3
H
SiCH3
CH3
H
SiCH3
H
Cl
SiCH2CH2SiHCH3 CH3
H
CH3CH3
SiCl
H
Cl
Cl
150
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
25
DIALKYLSILYL REDUCING AGENTSTABLE 4REDUCING AGENT STRUCTURE
COMMENTS
SID4230.0DIMETHYLSILANE[1111-74-6]TSCA
SiHCH3
CH3
H
Very low boiling point silane that is a gas at atmospheric
conditions.
SID3342.0DI-tert-BUTYLSILANE[30736-07-3]
H3CCCH3
H3C Si
CH3C
CH3H3C
H
H
Sterically-hindered silane reducing agent.
SID3368.0DICHLOROSILANE[4109-96-0]TSCA
HSi
H
Cl
Cl
Gives improved yields in reduction of imines over that of
trichlorosilane.56
SID3368.2DICHLOROSILANE, 25%in xylene[4109-96-0]TSCA
HSi
H
Cl
Cl
Easier to handle form of dichlorosilane.
SID3415.0DIETHYLSILANE[542-91-6]TSCA
CH3CH2Si
H
HCH3CH2
Used in the in-situ preparation of diborane and
haloboranes.157
SID4559.0DIPHENYLSILANE[775-12-2]TSCA
SiH
H
Used in the preparation of silyl-substituted alkylidene
complexes of tantalum.177 Used in the ionic reduction of enones to
saturated ketones.178 Used in the reductivecyclization of
unsaturated ketones.179,180 Reduces estersin the presence of zinc
hydride catalyst.53 Reduces -haloketones in presence of Mo(0).181
Reduces thio esters toethers.22 Reduces esters to alcohols with Rh
catalysis.49
Employed in the asymmetric reduction of methyl ketones114
and other ketones.182,183 Reductively cleaves allyl
acetates.184
SIP6742.0PHENYLMETHYLSILANE[766-08-5]TSCA
SiCH3
H
H
Used in the preparation of silyl-substituted alkylidene
complexes of tantalum.177
151
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
MONO-SUBSTITUTED SILANE REDUCING AGENTSTABLE 5REDUCING AGENT
STRUCTURE COMMENTS
SIH6166.2n-HEXYLSILANE[1072-14-6]TSCA
SIO6635.0n-OCTADECYLSILANE[18623-11-5]TSCA
SIO6712.5n-OCTYLSILANE[871-92-1]TSCA
SIP6750.0PHENYLSILANE[694-53-1]TSCA
Employed in the reduction of esters to ethers.185
Reduces ,-unsaturated ketones to saturated ketones in the
presence of tri-n-butyltin hydride.186 Reduces tin amides to tin
hydrides.187 Used in the tin-catalyzed reduction of nitroalkanes to
alkanes.188 Reduces -halo ketones in presence of Mo(0).181
SILOXANE-BASED SILANE REDUCING AGENTSTABLE 6REDUCING AGENT
STRUCTURE COMMENTS
SIO6696.5OCTAKIS(DIMETHYLSIL-OXY)-T8-SILSESQUIOXANE[125756-69-6]
Solid siloxane reducing agent. Offers 8 Si-H bonds. Potential
for easy removal of silicon by-products.
SIH6117.01,1,3,3,5,5-HEXAMETHYL-TRISILOXANE[1189-93-1]TSCA
High molecular weight silane reducing agent.
SIP6718.0PENTAMETHYLCYCLO-PENTASILOXANE, 90%[6166-86-5]TSCA
SIH5844.0HEPTAMETHYLTRISIL-OXANE[2895-07-0]
152
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
SIP6736.5PHENYLHYDROCYCLOSIL-OXANES, contains linears.
High-boiling siloxane reducing agent.
SIP6826.0PHENYLTRIS(DIMETHYLSILOXY)SILANE,
95%[18027-45-7]TSCA
High molecular weight silane reducing agent.
SIT7274.01,1,3,3-TETRAISOPROPYL-DISILOXANE[18043-71-5]
Sterically-hindered silane reducing agent with potential for
diastereoselective reductions.
SIT7278.0TETRAKIS(DIMETHYL-SILOXY)SILANE[17082-47-2]TSCA
High molecular weight silane reducing agent.
SIT7530.01,3,5,7-TETRAMETHYL-CYCLO-TETRASILOXANE[2370-88-9]TSCA
High molecular weight silane reducing agent.
SIT7546.01,1,3,3-TETRAMETHYL-DISILOXANE[30110-74-8]TSCA
Reduces aromatic aldehydes to benzyl halides.38 Used in the
reductive halogenation of aldehydes and epoxides.189
SIT8721.0TRIS(TRIMETHYLSILOXY)-SILANE[1873-89-8]
High molecular weight silane reducing agent.
METHYLHYDROSILOXANE-DIMETHYLSILOXANE CO-POLYMERSHMS-013 through
HMS-501having various MWs, vis-cosities, and hydride
content.[68037-59-2]TSCA
Potential reducing agents in the mode of HMS-991 or HMS-992.
153
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
HMS-991 or HMS-992POLYMETHYLHYDROSILOXANE[63148-57-2]TSCA
Reduces lactones to lactols.55 Reduces aldehydes, ketones,
esters, lactones, triglycerides and epoxides to alcohols with zinc
hydride catalysis.52 With titanium tetraisopropoxide catalysis,
carries out reductive amination of ketones and aldehydes82 and the
reduction of acids or esters to 1 alcohols.50 With TBAF catalysis,
selectively reduces aldehydes over ketones.43 Used to generate
tri-n-butyltin hydride in-situ and in a one-pot
hydrostannylation/Stille coupling sequence.190 Reduces esters to
alcohols.54
GERMANIUM AND TIN-BASED REDUCING AGENTSTABLE 7REDUCING AGENT
STRUCTURE COMMENTS
SNT8130TRI-n-BUTYLTIN HYDRIDE[688-73-3]TSCA
Has been reviewed.80 Catalyzes the Si-H reduction of
,-unsaturated ketones.186 Useful in the reductive amination of
ketones and aldehydes to form 3 amines.81
GET8100TRI-n-BUTYLGERMANE[998-39-0]
Reduces acid chlorides to aldehydes in presence of Pd(0).83
Effects free-radical reductive addition of alkyl halides to
olefins.191 Reduces benzylic chlorides 70x faster than silyl
hydrides.192
GET8660TRIPHENYLGERMANE[2816-43-5]
Readily adds to terminal acetylenes and olefins.193 Used in the
reductive alkylation of acrylonitrile and enones.84
GET8560TRIMETHYLGERMANE[1449-63-4]
Effects halogen displacement of alkyl halides with hydrogen when
exposed to UV.194
154
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
1REFERENCES:
Arkles, B., Silanes, In 1. The Kirk Othmer Encyclopedia of
Chemical Technology, 4th Ed., Kroschwitz, J. I., Howe-Grant, M.,
Eds.; Wiley: New York, 1997, Vol. 22, p38.Lalonde, M.; Chan, T. H.
2. Synthesis, 1985, 817.Nelson, T. D.; Crouch, R. D. 3. Synthesis,
1996, 1031.Silicon-Based Blocking Agents, Larson, G. L. Ed.;
4.Gelest, Inc. 1999.Walsh, R. 5. Acc. Chem. Res., 1981, 14, 246.
Walsh, R. Bond Dissociation Energies in Organosilicon Compounds, In
Silicon, Germanium, Tin & Metal Alkoxides Diketonates and
Carboxylates, Arkles, B. Ed.; Gelest, Inc. 1998, pp
92-99.Chatgilialoglu, C. 6. Chem. Rev. 1995, 95, 1229.Ding, L.;
Marshall, P. 7. J. Am. Chem. Soc. 1992, 114,5754. Brook, M. A.
Silicon in Organic, Organometallic, and Polymer Chemistry John
Wiley and Sons, Inc.: New York, 2000, pp 171-188.Colvin, E. 8.
Silicon in Organic Synthesis, pp 325-336, Butterworths, New York,
1981.Weber, W. P. 9. Silicon Reagents for Organic
Synthesis,Springer-Verlag, New York, 1983, pp 288-297.Kursanov, D.
N.; Parnes, Z. N. 10. Russ. Chem. Rev. (Engl. Transl.) 1969, 38,
812.Kursanov, D. N.; Parnes, Z. N.; Loim, N.M. 11. Synthesis,1974,
633.Kursanov, D.N. et al. 12. Ionic Hydrogenation and Related
Reactions; Harwood Academic Publishers, Chur, Switzerland,
1985.Nagai, Y. Org. Prep. Proced. Int. 13. 1980, 12, 13.Larson, G.
L.; Fry, J. L. 14. Ionic and Organometallic-Catalyzed Organosilane
Reductions, Wipf, P., Ed.; Wiley, 2007, accepted for
publication.Chatgilialoglu, C.; Ferreri, C.; Gimisis, T. 15.
Tris(trimethylsilyl)silane in Organic Synthesis, In The Chemistry
of Organic Silicon Compounds, Rappoport, Z.; Apeloig, Y. Eds.,
Wiley Chichester, 1998, Vol. 2 Chap. 25, p. 1539 ff.Chatgilialoglu,
C. 16. Acc. Chem. Res. 1992, 25, 188.Chatgilialoglu, C.; Griller,
D.; Lesage, M. 17. J. Org. Chem.1988, 53, 3641.Chatgilialoglu, C.;
Griller, D.; Lesage, M. 18. J. Org. Chem.1989, 54, 2492.Sano, H.;
Ogata, M.; Migita, T. 19. Chem. Lett. 1986, 77.Gimisis, T. et al.
20. Tetrahedron Lett. 1995, 36, 3897.Ballestri, M. et al. 21. J.
Org. Chem. 1991, 56, 678. Jang, D. O.; Song, S. H. 22. Synlett.
2000, 811.Carey, F. A.; Tremper, H. S. 23. J. Am. Chem. Soc. 1968,
90,2578.Carey. F. A.; Tremper, H. S. 24. J. Org. Chem. 1971, 36,
758.Adlington, M. G.; Orfanopoulos, M.; Fry, J. L. 25. Tetrahedron
Lett. 1976, 2955.Fry, J. L. U.S. Patent 4,130,574, 26. 1978.Fry, J.
L. private communication.27.Barclay, L. R. C.; Sonawane, H. R.;
MacDonald, M. C. 28.Can. J. Chem. 1972, 50, 281.Baer, H. H.;
Zamkanei, M. 29. J. Org. Chem. 1988, 53, 4786. Gevorgyan, V.;
Rubin, M.; Benson, S.; Liu, J.-X.; 30.Yamamoto, Y. J. Org. Chem.
2000, 65, 6179.Orfanopoulos, M.; Smonou, I. 31. Synth. Commun.
1988, 18,
833.Hanaoka, M.; Yoshida, S.; Mukai, C. 32. Tetrahedron
Lett.1985, 26, 5163.Wustrow, D. J.; Smith, III, W. J.; Wise, L. D.
33. Tetrahedron Lett. 1994, 35, 61.Whitmore, F. C.; Pietrusza, E.
W. Sommer, L. H. 34. J. Am. Chem. Soc. 1947, 69, 2108.Doyle, M. P.
et al. 35. J. Organomet. Chem. 1976, 117, 129. Becker, B.; Corriu,
R. J. P.; Gurin, C.; Henner, B.; Wang, 36.Q. J. Organomet. Chem.
1989, 359, C33. Hirano, K.; Fujita, K.; Yorimitsu, H.; Shinokubo,
H.; 37.Oshima, K. Tetrahedron Lett. 2004, 45, 2555.Boukherroub, R.;
Chatgilialoglu, C.; Manuel, G. 38.Organometallics 1996, 15,
1508.Keinan, E.; Greenspoon, N. 39. Israel J. Chem. 1984, 24,
82.Perez, D.; Greenspoon, N.; Keinan, E. 40. J. Org. Chem. 1987,
52, 5570.Pri-Bar, I.; Buchman, O. 41. J. Org. Chem. 1986, 51,
734.Lipshutz, B. H.; Tomioka, T.; Sato, K. 42. Synlett 2001,
970.Kotsuki, H.; Datta, P. K.; Hayakawa, H.; Suenaga, H.
43.Synthesis 1995, 1348.Zdanovich, V. I.; Kudryavtsev, R. V.;
Kursanov, D. N. 44. Bull.Acad. Sci. USSR, Div. Chem. Sci. (Engl.
Transl.) 1970, 19,427; Chem. Abstr. 1970, 73, 3550.
Trost, B. M.; Rise, F. 45. J. Am. Chem. Soc. 1987, 109,
3161.Trost, B. M.; Lee, D. C. 46. J. Am. Chem. Soc. 1988,
110,7255.Oh, C. H.; Park, S. J. 47. Tetrahedron Lett. 2003, 44,
3785.
Bolestova, G. I.; Parnes, Z. N.; Kursanov, D. N. 48. J. Org.
Chem. USSR (Engl. Transl.) 1979, 15, 1129; Chem. Abstr.
1979, 91, 140651.Roy, G. 49. Synth. Commun. 1983, 13,
459.Larsen, J. W.; Chang, L. W. 50. J. Org. Chem. 1979,
44,1168.Harrod, J. F.; Shu, R.; Woo, H.-G.; Samuel, E. 51. Can. J.
Chem. 2001, 79, 1075.Hao, L.; Harrod, J. F.; Lebuis, A.-M.; Mu, Y.;
Shu, R.; 52.Samuel, E.; Woo, H.-G. Angew. Chem., Int. Ed. Engl.
1998, 37, 3126.Imagawa, H.; Tsuchihashi, T.; Singh, R. K.;
Yamamoto, H.; 53.Sugihara, T.; Nishizawa, M. Org. Lett. 2003, 5,
153.Gevorgyan, V.; Rubin, M.; Benson, S.; Liu, J.-X.; 54.Yamamoto,
Y. J. Org. Chem. 2000, 65, 6179.Harvey, J. A.; Ogliaruso, M. A. 55.
J. Org. Chem. 1976, 41,3374.Matsubara, K.; Iura, T.; Maki, T.;
Nagashima, H. J. 56. J. Org. Chem. 2002, 67, 4985.Bajracharya, G.
B.; Nogami, T.; Jin, T.; Matsuda, K.; 57.Gevorgyan, V.; Yamamoto,
Y. Synthesis 2004, 308.Gevorgyan, V.; Rubin, M.; Liu, J-X.;
Yamamoto, Y. 58. J. Org. Chem. 2001, 66, 1672.Barr, K. J.; Berk, S.
C.; Buchwald, S. L. 59. J. Org. Chem.1994, 59, 4323.Berk, S. C.;
Kreutzer, K. A.; Buchwald, S. L. 60. J. Am. Chem. Soc. 1991, 113,
5093.Verdaguer, X.; Hansen, M. C.; Berk, S. C.; Buchwald, S. 61.L.
J. Org. Chem. 1997, 62, 8522.Verdaguer, X.; Berk, S. C.; Buchwald,
S. L. 62. J. Am. Chem. Soc. 1995, 117, 12641.Igarashi, M.; Mizuno,
R.; Fuchikami, T. 63. Tetrahedron Lett.
155
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
22001, 42, 2149.Davis, A. P.; Hegarty, S. C. 64. J. Am. Chem.
Soc. 1992, 114,2745.Newman, M. S.; Kanakarajan, K. 65. J. Org.
Chem. 1980, 45,2301.Ojima, I.; Kumagai, M. 66. J. Organomet. Chem.
1976, 111,43.Revis, A.; Hilty, T. K. 67. Tetrahedron Lett. 1987,
28, 4809.Freira, M.; Whitehead, A. J.; Tocher, D. A.; Motherwell,
W. 68.B. Tetrahedron 2004, 60, 2673.Kursanov, D. N. et al. 69.
Dokl. Chem. (Engl. Transl.) 1968,179, 328.Doyle, M. P. et al. 70.
J. Org. Chem. 1974, 39, 2740. Fry, J. L. et al. 71. J. Org. Chem.
1978, 43, 374. Sassaman, M. B. et al. 72. J. Org. Chem. 1987, 52,
4314.West, C. T. et al. 73. J. Org. Chem. 1973, 38, 2675.Aizpurua,
J. M.; Lecea, B.; Palomo, C. 74. Can. J. Chem.1986, 64,
2342.Aizpurua, J. M.; Palomo, C. 75. Tetrahedron Lett. 1984,
25,1103.Lecea, B.; Aizpurua, J. M.; Palomo, C. 76. Tetrahedron
1985,41, 4657.Akhrem, I. S.; Dene, M.; Volpin, M. E. 77. Bull.
Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.) 1973, 21,
897.Deneux, M. et al. 78. Bull. Soc. Chim. Fr. 1973, 2638.Fujita,
M.; Hiyama, T. 79. J. Org. Chem. 1988, 53, 5405.Chuit, C. et al.
80. Synthesis 1982, 981.Kobayashi, Y.; et al. 81. Tetrahedron 1997,
53, 1627.Doyle, M. P.; DeBruyn, D. J.; Donnelly, S. J.; Kooistra,
D. 82.A.; Odubela, A. A.; West, C. T.; Zonnebelt, S. M. J. Org.
Chem. 1974, 39, 2740.Dub, D.; Scholte, A. A. 83. Tetrahedron Lett.
1999, 40,2295.Ojima, I.; Kogure, T. 84. Organometallics 1982, 1,
1390.Rupprecht, K. M. et al. 85. J. Org. Chem. 1991, 56, 6180.Yato,
M.; Homma, K.; Ishida, A. 86. Heterocycles 1998, 49,233.Ito, H. et
al. Synlett. 87. 2000, 475. Sassaman, M. B.; Prakash, G. K. S.;
Olah, G. A. 88.Tetrahedron 1988, 44, 3771.Nicolaou, K. C.; Hwang,
C.-K.; Nugeil, D. A. 89. J. Am. Chem. Soc. 1989, 111, 4136.Carreo,
M. C.; Mazery, R. D.; Urbano, A.; Colobert, F.; 90.Solladi, G. Org.
Lett. 2004, 6, 297.Mulholland, R. L.; Chamberlin, A. R. 91. J. Org.
Chem. 1988,53, 1082.Onishi, Y.; Ogawa, D.; Yasuda, M.; Baba, A. 92.
J. Am. Chem. Soc. 2002, 124, 13690.Lecea, B.; Aizpurua, J. M.;
Palomo, C. 93. Tetrahedron 1985,41, 4657.Chandrasekhar, S.; Reddy,
Ch. R.; Babu, B. N. 94. J. Org. Chem. 2002, 67, 9080.Miura, K.;
Ootsuka, K.; Suda, S.; Nishikori, H.; Hosomi, A. 95.Synlett 2001,
1617.
Keinan, E.; Greenspoon, N. 96. J. Am. Chem. Soc. 1986,
108, 7314.
Blazejewski, J. C.; Dorme, R.; Wakselman, C. 97. J. Chem.
Soc., Perkin Trans. 1 1987, 1861.
Igarashi, M.; Fuchikami, T. 98. Tetrahedron Lett. 2001, 42,
1945.
Bower, S.; Kreutzer, K. A.; Buchwald, S. L. 99. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1515.Ohta, T. et al. 100.
Tetrahedron Lett. 1999, 40, 6963.Breedon, S. W.; Lawrence, N. J.
101. Synlett. 1994, 833. Drew, M. D. et al. 102. Synlett. 1997,
989.Mimoun, H.; 103. J. Org. Chem. 1999, 64, 2583.Barr, K. J.;
Berk, S. C.; Buchwald, S. L. 104. J. Org. Chem.1994, 59, 4323.
Reding, M. T.; Buchwald, S. L. 105. J. Org. Chem. 1995,
60,7884.Verdaguer, X. et al. 106. J. Org. Chem. 1997, 62, 8522.
Okamoto, H.; Kato, S. 107. Bull. Chem. Soc. Jpn. 1991,
64,3466.Fujita, M.; Oishi, H.; Hiyama, T. 108. Chem. Lett. 1986,
837.Chandrasekhar, S.; Reddy, Y. R.; Reddy, Ch. R. 109. Chem.Lett.
1998, 1273.Tokuyasu, T.; Ito, T.; Masuyama, A.; Nojima, M.
110.Heterocycles 2000, 53, 1293.Hinman, M. M.; Heathcock, C. H.
111. J. Org. Chem. 2001,66, 7751.Billard, T.; Langlois, B. R. 112.
J. Org. Chem. 2002, 67, 997.Auerbach, J.; Zamore, M.; Weinreb, S.
M. 113. J. Org. Chem.1976, 41, 725.Freidinger, R. M.; Hinkle, J.
S.; Perlow, D. S.; Arison, B. H. 114.J. Org. Chem. 1983, 48,
77.Lanzilotti, A. E.; Littell, R.; Fanshawe, W. J.; McKenzie. T.
115.C.; Lovell, F. M. J. Org. Chem. 1979, 44, 4809.Comins, D. L.;
Myoung, Y. C. 116. J. Org. Chem. 1990, 55,292.Akhrem, A. A.;
Moiseenkov, A. M.; Krivoruchko, V. A. 117. Bull.Acad. Sci. USSR,
Div. Chem. Sci. (Engl. Transl.) 1973, 22,1745; Chem. Abstr. 1979,
79, 105102.Kursanov, D. N.; Parnes, Z. N.; Bolestova, G. I. 118.
Dokl.Chem. (Engl. Transl.) 1968, 181, 726.Parnes, Z. N. et al. 119.
Dokl. Chem. (Engl. Transl.) 1966, 166,32.Kursanov, D. N. et al.
120. Tetrahedron 1967, 23, 2235.Doyle, M. P.; McOsker, C. C. 121.
J. Org. Chem. 1978, 43,693.Kursanov, D. N. et al. 122. Dokl. Chem.
(Engl. Transl.) 1972,205, 562.Carey, F. A.; Tremper, H. S. 123. J.
Org. Chem. 1969, 34, 4.Kursanov, D. N. et al. 124. Bull. Acad. Sci.
USSR, Div. Chem. Sci. (Engl. Transl.) 1979, 28, 746.Lipshutz, B. H.
et al. 125. Tetrahedron Lett. 1998, 39, 4627.Ito, H. et al. 126.
Tetrahedron Lett. 1997, 38, 8887.Takano, S.; Moriya, M.; Ogasawara,
K. 127. Tetrahedron Lett.1992, 33, 1909.Serebryankova, T. A. et
al.128. Bull. Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.)
1972, 21, 1633.Julia, M. Roy, P. 129. Tetrahedron 1986, 42,
4991.Zdanovich, V. I.; Kudryatsev, R. V.; Kursanov, D. N. 130.
Bull.Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.) 1970,
19,427.Parnes, Z. N.; Khotimskaya, G. A.; Kudryavtsev, R. V.;
131.Kursanov, D. N. Bull. Acad. Sci. USSR, Div. Chem. Sci. (Engl.
Transl.) 1972, 21, 854; Chem. Abstr. 1972, 77,87932.Parnes, Z. N.;
Bolestova, G. I.; Kursanov, D. N. 132. Bull.Acad. Sci. USSR, Div.
Chem. Sci. (Engl. Transl.) 1972, 21,1927; Chem. Abstr. 1973, 78,
28811.
156
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
3Doyle, M. P.; West, C. T. 133. J. Org. Chem. 1975, 40,
3829.Semmelhack, M. F.; Misra, R. N. 134. J. Org. Chem. 1982, 47,
2469.Kobayashi, Y.; Ito, Y.; Terashima, S. 135. Bull. Chem. Soc.
Jpn.1989, 62, 3041.Smonou, I. 136. Tetrahedron Lett. 1994, 35,
2071.Lewis, M. D.; Cha, J. K.; Kishi, Y. 137. J. Am. Chem.
Soc.1982, 104, 4976.Nishiyama, Y. et al. 138. Chem. Lett. 1997,
165.Carter, M. B. et al. 139. J. Am. Chem. Soc. 1994, 116,
11667.Yun, J.; Buchwald, S. L. 140. J. Am. Chem. Soc. 1999,
121,5640.Lipshutz, B. H.; Servesko, J. M.; Petersen, T. B.; Papa,
P. 141.P.; Lover, A. A. Org. Lett. 2004, 6, 1273.Yun, J.; Buchwald,
S. L. 142. Org. Lett. 2001, 3, 1129.Lipshsutz, B. H.; Servesko, J.
M.; Taft, B. R. 143. J. Am. Chem. Soc. 2004, 126, 8352.Verdaguer,
X.; Lange, U. E. W.; Buchwald, S.L. 144. Angew. Chem. Int. Ed.
Engl. 1998, 37, 1103.Verdaguer, X.; Lange, U. E. W.; Reding, M. T.;
Buchwald, 145.S. L. J. Am. Chem. Soc. 1996, 118, 6784.Reding, M.
T.; Buchwald, S. L. 146. J. Org. Chem. 1998, 63,6344.Willoughby, C.
A.; Buchwald, S. L. 147. J. Org. Chem. 1993,58, 7627.Neumann, W. P.
148. Synthesis, 1987, 665.Suwa, T. et al. 149. Synlett. 2000,
556.Chandrasekhar. S.; Reddy, Ch. R.; Ahmed, M. 150. Synlett.2000,
1655.Geng, L.; Lu, X. 151. J. Organomet. Chem. 1989, 376, 41.Pike,
P.; Hershberger, S.; Hershberger, J. 152. Tetrahedron.1988, 44,
6295.Anderson, H. H. 153. J. Am. Chem. Soc. 1958, 80, 5083.Mehta,
A. et al. 154. Tetrahedron Lett. 1992, 33, 5441.Dorow, R. L.;
Gingrich, D. E. 155. Tetrahedron Lett. 1999, 40,467.Kato, J.;
Iwasawa, N.; Mukaiyama, T. 156. Chem. Lett. 1985,743.Soundararajan,
R.; Matteson, D. S. 157. Organometallics,1995, 14, 4157.Pearson, D.
A. et al. 158. Tetrahedron Lett. 1989, 30, 2739.Sano, H.;
Toshimitsu, T.; Migita, T. 159. Synthesis, 1988, 402.Boyer, J. et
al. 160. Tetrahedron, 1981, 37, 2165.Corriu, R. J. P.; Perz, R.;
Reye, C. 161. Tetrahedron, 1983, 39,999.Apeloig, Y.; Nakash, M.
162. J. Am. Chem. Soc. 1994, 116,10781.Gimisis, T. et al. 163.
Tetrahedron Lett. 1995, 36, 6781.Davis, A. P.; Hegaarty, S. C. 164.
J. Am. Chem. Soc. 1992,114, 2745.Bergen, S. H. et al. 165. J. Am.
Chem. Soc. 1992, 114, 2121.Anwar, S.; Davis, A. P. 166. Tetrahedron
1988, 44, 3761.Fujita, M.; Hiyama, T. 167. J. Am. Chem. Soc. 1984,
106,4629.Taylor, S. J.; Morken, J. P. 168. J. Am. Chem. Soc. 1999,
121,12202.Fujita, M.; Hiyama, T. 169. J. Org. Chem. 1988, 53,
5415.Ito, H. et al. 170. Synlett. 2000, 479.Eguchi, M. et al. 171.
Tetrahedron Lett. 1993, 34, 915.Mori, A. et al. 172. Tetrahedron,
1999, 55, 4573.Benkeser, R. A. 173. Acc. Chem. Res. 1971, 4,
94.
Benkeser, R. A.; Gaul, J. M. 174. J. Am. Chem. Soc. 1970,
92,720.Benkeser, R. A. et al. 175. J. Am. Chem. Soc. 1970, 92,
3232.Fry, J. L. 176. Chem. Commun. 1974, 501.Diminnie, J. B.; Xue,
Z. 177. J. Am. Chem. Soc. 1997, 119,12657.Kablaoni, N. M.;
Buchwald, S. L. 178. J. Am. Chem. Soc.1995, 117, 6785. Kablaoni, N.
M.; Buchwald, S. L. 179. J. Am. Chem. Soc.1996, 118, 3182.Perez,
D.; Greenspoon, N.; Keinan, E. 180. J. Org. Chem.1987, 52,
5570.Enders, D.; Gielen, H.; Breuer, K. 181. Tetrahedron:
Asymmetry1997, 8, 3571.Lee, S. et al. 182. Tetrahedron: Asymmetry
1997, 8, 4027. Sudo, A.; Yoshida, H.; Saigo, K. 183. Tetrahedron:
Asymmetry1997, 8, 3205.Keinan, E.; Greenspoon, N. 184. J. Org.
Chem. 1983, 48,3545.Mao, Z.; Gregg, B. T.; Cutler, A. R. 185. J.
Am. Chem. Soc.1995, 117, 10139.Hays, D. S.; Scholl, M.; Fu, G. C.
186. J. Org. Chem. 1996, 61,6751.Hays, D. S.; Fu, G. C. 187. J.
Org. Chem. 1997, 62, 7070.Tormo, J.; Hays, D. S.; Fu, G. C. 188. J.
Org. Chem. 1998, 63,5296.Fujisawa, T.; Kawashima, M.; Ando, S. 189.
Tetrahedron Lett.1984, 25, 3123.Maleczka, Jr., R. E. et al. 190.
Org. Lett. 2000, 2, 3655.Hersberger, J. 191. Tetrahedron Lett.
1986, 26, 6289.Mayr, H. et al. 192. Angew. Chem. Int. Ed. Engl.
1992, 31,1046.Nozaki, K. et al. 193. Bull. Chem. Soc. Jpn. 1990,
63, 2268.Coates, et al. 194. J. Chem. Soc. Perk. Trans. II 1978,
725.
157
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com
-
158
Gelest, Inc.
AZmax TEL: 035543-1630 FAX: 03-5543-0312 www.azmax.co.jp (215)
547-1015 FAX: (215) 547-2484 www.gelest.com