Chris Borths MacMillan Group Meeting October 3, 2001 I. Definition II. Oxidations III. Reductions IV. Alkylations V. Lewis base catalysis R e v i e w s: L A C: Berrisford, D.J.; Bolm, C.; Sharpless, K.B. Ang. Chem. Int. Ed. Engl. 1995, 34, 1059. N o n - L i n e a r E f f e c t s: Girard, C.; Kagan, H.B. Angew. Chem. Int. Ed. Engl. 1998, 37, 2922. Blackmond, D.G. J. Am. Chem. Soc. 1997, 119, 12934. A s y m m e t r i c A c t i v a t i o n: Mikami, K.; Terada, M.; Korenaga, T.; Matsumoto, Y.; Ueki, M.; Angelaud, R. Angew. Chem. Int. Ed. Engl. 2000, 112, 3532. Ligand Accelerated Catalysis (LAC)
12
Embed
Ligand Accelerated Catalysis (LAC)chemlabs.princeton.edu/macmillan/wp-content/uploads/sites/6/borths-LAC.pdf · Multiple metal-ligand species are active epoxidation catalysts OR Ti
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Yamasaki, S.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2001, 123, 1256.
! An enantioselective variant has been proposed and is under development.
+ BTSP + TMSCN
1) Zr(OtBu)4 : ligand : H2O (1:1:1) ClCH2CH2Cl
2) KF, MeOH
OH
CN
OH
OH
Ph Ph
Ph Ph
O
O
Et
Et
LIGAND
85% yield62% ee
Pt
PtPt
Platinum-Catalyzed Hydrogenation of Ethyl Pyruvate
! Chincona alkaloids have been shown to adsorb to Pt surfaces in an ordered pattern with uniformly shaped pores.
! Relative reaction rates from kinetic data suggest a ligand acceleration effect of !13.
Blaser, H.U.; Jalett, H.P.; Lottenbach, W.; Studer, M. J. Am. Chem. Soc. 2000, 122, 12675.Thomas, J.M. Angew. Chem. Int. Ed. Engl. Adv. Mater. 1989, 28, 1079.Garland, M.; Blaser, H.U. J. Am. Chem. Soc. 1990, 112, 7048.
O
Me CO2Et
OH
Me CO2Et
Pt/Al2O3, H2
modifier
N
HOMe
N
Et
ee 93%
N
HOH
N
Et
ee 20%
HON
ee 75%
NH2
ee 82%
N
N
RO H
Me
OEtO
Pt
MeO
H
! Author's rendition of proposed transition states
PtPt
N
RO HO
EtO
R
H
O
Me
Pt Surface Modifiers
Ruthenium-Catalyzed Transfer Hydrogenation
! Only aryl ketones are reduced enantioselectively.
20 mol % RuCl2(PPh3)3
26 mol % ligand
iPrOH / iPrOK Me
OH
Me
O
Ligand
none
time
20 h
6 h
conversion
5 %
93 %(94% ee)
Fe O
NPh
PPh3
R
Me
Et
iPr
20 mol % RuCl2(PPh3)3
26 mol % A
iPrOH / iPrOK Ar R
OH
Ar R
O
A
yields ! 75 %
Sammakia, T.; Strangeland, E.L. J. Org. Chem. 1997, 62, 6104.
ee (%)
! 84
96 (Ar = Ph)
88 (Ar = Ph)
Copper-Catalyzed Enolsilane Amination
! Amination reaction allows access to chiral building blocks: protected chiral hydrazines, hydrazino alcohols,
and oxazolidones.
Evans, D.A.; Johnson, D.S. Org. Lett. 1999, 1, 595.
XR
OTMS
ONNN
Troc
O O
N
O
N
O
Me Me
tBu tBu
Cu
2+
2 OTf-
ONNH
NTroc
O OR
X
O
1-10 mol %
CF3CH2OH
X = Ar, pyrrole, StBuR = Me, Et, iPr, tBu, Ph, Bn
+
yield ! 64ee ! 96
NN
O
L2CuO
N
O
Ph OTMS
R
Troc NN
O
Ph OTMS
R
Troc ON
O
proposed intermediates
! Evidence for LAC: Use of excess Cu(OTf)2 (50 mol %) relative to ligand (2 & 10 mol %) shows no significant
decrease in enantioselectivity (99 % vs. 96 % ee).
ROH
ROTMS
Conjugate Additions of Dialkylzinc Reagents
O
R HEt2Zn+
2 mol % catalyst
! Diamines and amino-alcohols accelerate the reaction of dialklzinc reagents with aldehydes.
Et
OH
98 % ee
Me
NMe2
OH
CatalystO
Me
OH
99 % ee(using (C5H11)2Zn)
OH
Me
OH
Me
96 % ee
90 % ee
Me
OH
Me
61 % ee
Noyori, R.; Suga, S.; Kawai, K.; Okada, S.; Kitamura, M.; Oguni, N.; Hayashi, M.; Kaneko, T.; Matsuda, Y. J. Organomet. Chem. 1990, 382, 19.Noyori, R. Asymmetric Catalysis in Organic Synthesis; John Wiley and Sons, Inc.: New York, 1994.
! Without catalyst, no product is generated under reaction conditions.
Me2N
OZn
MeMe
ZnR
R
O
R
Ph
H
proposed T.S.
Titanium-Catalyzed Enantioselective Alkylation of Aldehydes