Dr. Wolf's CHM 201 & 202 14-1 Chapter 14 Chapter 14 Organometallic Compounds Organometallic Compounds
Dr. Wolf's CHM 201 & 202 14-1
Chapter 14Chapter 14Organometallic CompoundsOrganometallic Compounds
Dr. Wolf's CHM 201 & 202 14-2
Organometallic Nomenclature
Dr. Wolf's CHM 201 & 202 14-3
Metal is the parentMetal is the parentMetal is the parentMetal is the parent LiLi
CyclopropylCyclopropyllithiumlithium VinylVinylsodiumsodium
HH22CC CHCHNaNa
CHCH33CHCH22MgMgCHCH22CHCH33
DiethylDiethylmagnesiummagnesium
CHCH33MgMgII
MethylMethylmagnesiummagnesiumiodideiodide
Dr. Wolf's CHM 201 & 202 14-4
Carbon-Metal BondsCarbon-Metal Bondsinin
Organometallic CompoundsOrganometallic Compounds
Dr. Wolf's CHM 201 & 202 14-5
FF 4.04.0 HH 2.12.1
OO 3.53.5 CuCu 1.91.9
NN 3.03.0 ZnZn 1.61.6
CC 2.52.5 AlAl 1.51.5
HH 2.1 2.1 MgMg 1.21.2
LiLi 1.01.0
NaNa 0.90.9
KK 0.80.8
ElectronegativitiesElectronegativities
Dr. Wolf's CHM 201 & 202 14-6
Polarity of BondsPolarity of BondsPolarity of BondsPolarity of Bonds
RR XX++ ––
RR MM–– ++
organometallics are a organometallics are a source of nucleophilic source of nucleophilic
carboncarbon
Dr. Wolf's CHM 201 & 202 14-7
Polarity of BondsPolarity of BondsPolarity of BondsPolarity of Bonds
CHCH33FF CHCH33LiLi
Dr. Wolf's CHM 201 & 202 14-8
Preparation of Organolithium CompoundsPreparation of Organolithium Compounds
Dr. Wolf's CHM 201 & 202 14-9
same for same for ArAr—X—X
An oxidation-reduction reaction: An oxidation-reduction reaction: carbon is reduced carbon is reduced
Organolithium CompoundsOrganolithium CompoundsOrganolithium CompoundsOrganolithium Compounds
RR X + 2LiX + 2Li RR Li + LiXLi + LiX
normally prepared by reaction of alkyl halides normally prepared by reaction of alkyl halides with lithiumwith lithium
Dr. Wolf's CHM 201 & 202 14-10
ExamplesExamplesExamplesExamples
(CH(CH33))33CCl + 2LiCCl + 2Li
diethyldiethyletherether
––10°C10°C
(CH(CH33))33CLi + LiClCLi + LiCl
(75%)(75%) BrBr + 2Li+ 2Li
diethyldiethyletherether
35°C35°C
LiLi + LiBr+ LiBr
(95-99%)(95-99%)
Dr. Wolf's CHM 201 & 202 14-11
Electron BookkeepingElectron BookkeepingElectron BookkeepingElectron Bookkeeping
RR X + LiX + Li [R[R X]X] + Li+ Li++••––
RR•• ++ •••• XX––
••
LiLi••••••RR LiLi
Dr. Wolf's CHM 201 & 202 14-12
Preparation of Organomagnesium Compounds:
Grignard Reagents
Dr. Wolf's CHM 201 & 202 14-13
same for same for ArAr—X—X
Grignard ReagentsGrignard ReagentsGrignard ReagentsGrignard Reagents
RR X + MgX + Mg RMgXRMgX
prepared by reaction of alkyl halides prepared by reaction of alkyl halides with magnesiumwith magnesium
Diethyl ether is most often used solvent. Diethyl ether is most often used solvent. Tetrahydrofuran is also used.Tetrahydrofuran is also used.
Dr. Wolf's CHM 201 & 202 14-14
ExamplesExamplesExamplesExamplesdiethyldiethyletherether
––10°C10°C(96%)(96%)
BrBr + Mg+ Mg
diethyldiethyletherether
35°C35°C
MgBrMgBr
(95%)(95%)
ClCl + Mg+ Mg
MgClMgCl
Dr. Wolf's CHM 201 & 202 14-15
RR X + MgX + Mg
Electron BookkeepingElectron BookkeepingElectron BookkeepingElectron Bookkeeping
[R[R X]X] + Mg+ Mg++••––
RR•• ++ •••• XX––
••
••••RR MgMg++
•• ••
MgMg++••
•••• XX––
Dr. Wolf's CHM 201 & 202 14-16
I > Br > Cl >> FI > Br > Cl >> F
RX > ArXRX > ArX
Order of ReactivityOrder of ReactivityOrder of ReactivityOrder of Reactivity
Dr. Wolf's CHM 201 & 202 14-17
certain groups cannot be present incertain groups cannot be present in
the solventthe solvent
the halide from which the Grignard reagent the halide from which the Grignard reagent
is preparedis prepared
the substance with which the Grignard the substance with which the Grignard reagent reactsreagent reacts
Forbidden GroupsForbidden GroupsForbidden GroupsForbidden Groups
Dr. Wolf's CHM 201 & 202 14-18
Anything with an OH, SH, or NH groupAnything with an OH, SH, or NH groupi.e. an acidic hydrogeni.e. an acidic hydrogen
Forbidden GroupsForbidden GroupsForbidden GroupsForbidden Groups
therefore cannot use Htherefore cannot use H22O, CHO, CH33OH, OH,
CHCH33CHCH22OH, etc. as solventsOH, etc. as solvents
cannot prepare Grignard reagent from cannot prepare Grignard reagent from substances such as HOCHsubstances such as HOCH22CHCH22Br, etc.Br, etc.
Dr. Wolf's CHM 201 & 202 14-19
Organolithium and Organomagnesium Compounds as Brønsted Bases
Dr. Wolf's CHM 201 & 202 14-20
Brønsted basicityBrønsted basicityBrønsted basicityBrønsted basicity
RR
MM
HH
OR'OR'
••••
••••
RR HH
OR'OR'••••
••••••••––
MM++
–– ++
Grignard reagents (Grignard reagents (MM = MgX) and = MgX) and organolithium reagents (organolithium reagents (MM = Li) are strong = Li) are strong bases.bases.
Dr. Wolf's CHM 201 & 202 14-21
ExampleExampleExampleExample
(100%)(100%)
+ H+ H22OO
++ LiOHLiOH
CHCH33CHCH22CHCH22CHCH22LiLi
CHCH33CHCH22CHCH22CHCH33
water is a stronger water is a stronger acid than butaneacid than butane
Dr. Wolf's CHM 201 & 202 14-22
ExampleExampleExampleExample MgBrMgBr
(100%)(100%)
+ CH+ CH33OHOH ++ CHCH33OMgBrOMgBr
methanol is a methanol is a stronger acid than stronger acid than benzenebenzene
Dr. Wolf's CHM 201 & 202 14-23
Table 14.2Table 14.2Approximate Acidities of HydrocarbonsApproximate Acidities of Hydrocarbons
Table 14.2Table 14.2Approximate Acidities of HydrocarbonsApproximate Acidities of Hydrocarbons
HydrocarbonHydrocarbon ppKKaa
(CH(CH33))33CCHH 7171
CHCH33CHCH33 6262
CHCH44 6060
EthyleneEthylene 4545
BenzeneBenzene 4343
AmmoniaAmmonia 3636
AcetyleneAcetylene 2626
WaterWater 1616
Hydrocarbons are Hydrocarbons are very weak acids.very weak acids.
Their conjugate Their conjugate bases are very bases are very strong bases.strong bases.
Grignard reagents Grignard reagents and organolithium and organolithium reagents are strong reagents are strong bases.bases.
Dr. Wolf's CHM 201 & 202 14-24
Acetylenic Grignard ReagentsAcetylenic Grignard ReagentsAcetylenic Grignard ReagentsAcetylenic Grignard Reagents
are prepared by an acid-base reactionare prepared by an acid-base reaction
CHCH33CHCH22MgMgBrBr
++CHCH33CHCH33
stronger acidstronger acid
weaker acidweaker acid
HCHC CHCH
HCHC CCMgMgBrBr
++
Dr. Wolf's CHM 201 & 202 14-25
Synthesis of Alcohols Using Synthesis of Alcohols Using
Grignard ReagentsGrignard Reagents
Dr. Wolf's CHM 201 & 202 14-26
Grignard reagents act as nucleophilesGrignard reagents act as nucleophilestoward the carbonyl grouptoward the carbonyl group
Grignard reagents act as nucleophilesGrignard reagents act as nucleophilestoward the carbonyl grouptoward the carbonyl group
RR
MgXMgX
CC
OO
••••
•••• ––MgXMgX++
–– ++RR CC
OO••••
•••• ••••
••••
RR CC
OHOH••••
HH33OO++
diethyldiethyletherether
two-step sequence two-step sequence gives an alcohol as gives an alcohol as the isolated product the isolated product
Dr. Wolf's CHM 201 & 202 14-27
formaldehydeformaldehyde to give primary alcohols to give primary alcohols
aldehydesaldehydes to give secondary alcohols to give secondary alcohols
ketonesketones to give tertiary alcohols to give tertiary alcohols
estersesters to give tertiary alcohols to give tertiary alcohols
Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:
Dr. Wolf's CHM 201 & 202 14-28
formaldehydeformaldehyde to give primary alcohols to give primary alcohols
Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:
Dr. Wolf's CHM 201 & 202 14-29
Grignard reagents react with Grignard reagents react with formaldehydeformaldehydeGrignard reagents react with Grignard reagents react with formaldehydeformaldehyde
RR
MgXMgX
CC
OO
••••
•••• ––MgXMgX++
–– ++RR CC
OO••••
•••• ••••
••••
RR CC
OHOH••••
HH33OO++
diethyldiethyletherether
product is a product is a primary alcoholprimary alcohol
HH HHHH
HH
HH
HH
Dr. Wolf's CHM 201 & 202 14-30
ExampleExampleExampleExample
diethyldiethyletherether
ClCl
MgMg
MgClMgCl
CC OO
HH
HH CCHH22OMgClOMgCl
HH33OO++
CCHH22OHOH
(64-69%)(64-69%)
Dr. Wolf's CHM 201 & 202 14-31
formaldehydeformaldehyde to give primary alcohols to give primary alcohols
aldehydesaldehydes to give secondary alcohols to give secondary alcohols
Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:
Dr. Wolf's CHM 201 & 202 14-32
Grignard reagents react with Grignard reagents react with aldehydesaldehydesGrignard reagents react with Grignard reagents react with aldehydesaldehydes
RR
MgXMgX
CC
OO
••••
•••• ––
–– ++RR CC
OO••••
•••• ••••
••••
RR CC
OHOH••••
HH33OO++
diethyldiethyletherether
product is a product is a secondary alcoholsecondary alcohol
HH R'R'HH
R'R'
HH
R'R'
MgXMgX++
Dr. Wolf's CHM 201 & 202 14-33
ExampleExampleExampleExample
diethyldiethyletherether
MgMg
CC OO
HH33CC
HH
HH33OO++
(84%)(84%)
CHCH33(CH(CH22))44CHCH22BrBr CHCH33(CH(CH22))44CHCH22MgBrMgBr
CHCH33(CH(CH22))44CHCH22CCHHCHCH33
OMgBrOMgBr
CHCH33(CH(CH22))44CHCH22CCHHCHCH33
OHOH
Dr. Wolf's CHM 201 & 202 14-34
formaldehydeformaldehyde to give primary alcohols to give primary alcohols
aldehydesaldehydes to give secondary alcohols to give secondary alcohols
ketonesketones to give tertiary alcohols to give tertiary alcohols
Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:Grignard reagents react with:
Dr. Wolf's CHM 201 & 202 14-35
Grignard reagents react with Grignard reagents react with ketonesketonesGrignard reagents react with Grignard reagents react with ketonesketones
RR
MgXMgX
CC
OO
••••
•••• ––MgXMgX++
–– ++RR CC
OO••••
•••• ••••
••••
RR CC
OHOH••••
HH33OO++
diethyldiethyletherether
product is a product is a tertiary alcoholtertiary alcohol
R"R" R'R'R"R"
R'R'
R"R"
R'R'
Dr. Wolf's CHM 201 & 202 14-36
ExampleExampleExampleExample
diethyldiethyletherether
MgMg
HH33OO++
(62%)(62%)
CHCH33ClCl CHCH33MgClMgCl OO CHCH33ClMgOClMgO CHCH33HOHO
Dr. Wolf's CHM 201 & 202 14-37
Organolithium reagents react with Organolithium reagents react with aldehydes and ketones in the same aldehydes and ketones in the same
way that Grignard reagents do.way that Grignard reagents do.
Synthesis of AlcoholsUsing Organolithium Reagents
Dr. Wolf's CHM 201 & 202 14-38
ExampleExampleExampleExample
(76%)(76%)
HH22CC CHLiCHLi ++
CCHH
OO
1. diethyl ether1. diethyl ether
2. H2. H33OO++ CHCH22CCHCHHCH
OHOH
Dr. Wolf's CHM 201 & 202 14-39
Synthesis of Acetylenic Alcohols
Dr. Wolf's CHM 201 & 202 14-40
Using Sodium Salts of AcetylenesUsing Sodium Salts of AcetylenesUsing Sodium Salts of AcetylenesUsing Sodium Salts of Acetylenes
HCHC CHCH
NaNHNaNH22
NHNH33
HCHC CCNaNa
HCHC CCNaNa ++1. NH1. NH33
2. H2. H33OO++
OO HOHO CC CCHH (65-75%)(65-75%)
Dr. Wolf's CHM 201 & 202 14-41
CHCHCHCH33(CH(CH22))33CC ++ CHCH33CHCH22MgMgBrBr
CCMgMgBrBrCHCH33(CH(CH22))33CC ++ CHCH33CHCH33
diethyl etherdiethyl ether
1. H1. H22CC OO2. H2. H33OO++
CCCCHH22OHOHCHCH33(CH(CH22))33CC
(82%)(82%)
Using Acetylenic Grignard ReagentsUsing Acetylenic Grignard ReagentsUsing Acetylenic Grignard ReagentsUsing Acetylenic Grignard Reagents
Dr. Wolf's CHM 201 & 202 14-42
Retrosynthetic Analysis
Retrosynthetic analysis is the process by Retrosynthetic analysis is the process by which we plan a synthesis by reasoning which we plan a synthesis by reasoning backward from the desired product (the backward from the desired product (the "target molecule")."target molecule").
Dr. Wolf's CHM 201 & 202 14-43
Retrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of Alcohols
CC
OHOH
Step 1 Step 1 Locate the carbon that bears the Locate the carbon that bears the hydroxyl group.hydroxyl group.
Dr. Wolf's CHM 201 & 202 14-44
Retrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of Alcohols
CC
OHOH
Step 2 Step 2 Disconnect one of the groups Disconnect one of the groups attached to this carbon.attached to this carbon.
Dr. Wolf's CHM 201 & 202 14-45
Retrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of Alcohols
CC
OHOH
Dr. Wolf's CHM 201 & 202 14-46
Retrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of AlcoholsRetrosynthetic Analysis of Alcohols
CC
OO
What remains is the combination of Grignard What remains is the combination of Grignard reagent and carbonyl compound that can be reagent and carbonyl compound that can be used to prepare the alcohol.used to prepare the alcohol.
MgXMgX
Dr. Wolf's CHM 201 & 202 14-47
ExampleExampleExampleExample CC
OHOH
CHCH33
CHCH22CHCH33
CC CHCH22CHCH33
OO
CHCH33MgXMgX
There are two There are two other other possibilities. possibilities.
Can you see Can you see them?them?
Dr. Wolf's CHM 201 & 202 14-48
SynthesisSynthesisSynthesisSynthesis
CC
OHOH
CHCH33
CHCH22CHCH33
CC CHCH22CHCH33
OO
1.1.
2. H2. H33OO++
CHCH33BrBrMgMg, diethyl ether, diethyl ether
CHCH33MgMgBrBr
Dr. Wolf's CHM 201 & 202 14-49
Preparation of Tertiary AlcoholsFrom Esters and Grignard Reagents
(also in Chapter 19)
Dr. Wolf's CHM 201 & 202 14-50
Grignard reagents react with estersGrignard reagents react with estersGrignard reagents react with estersGrignard reagents react with esters
RR
MgXMgX
CC
OO
••••
•••• ––MgXMgX++
–– ++RR CC
OO••••
•••• ••••
diethyldiethyletherether
OCHOCH33••••
•••• OCHOCH33••••
••••
R'R'R'R'
but species formed is but species formed is unstable and dissociates unstable and dissociates under the reaction under the reaction conditions to form a ketoneconditions to form a ketone
Dr. Wolf's CHM 201 & 202 14-51
Grignard reagents react with estersGrignard reagents react with estersGrignard reagents react with estersGrignard reagents react with esters
RR
MgXMgX
CC
OO
••••
•••• ––MgXMgX++
–– ++RR CC
OO••••
•••• ••••
diethyldiethyletherether
OCHOCH33••••
•••• OCHOCH33••••
••••
R'R'R'R'
––CHCH33OOMgXMgX
CC
OO
RR R'R'
••••••••
this ketone then goes this ketone then goes on to react with a on to react with a second mole of the second mole of the Grignard reagent to Grignard reagent to give a tertiary alcoholgive a tertiary alcohol
Dr. Wolf's CHM 201 & 202 14-52
ExampleExampleExampleExample
2 CH2 CH33MgBrMgBr ++ (CH(CH33))22CHCCHCOCHOCH33
OO
1. diethyl ether1. diethyl ether
2. H2. H33OO++
(CH(CH33))22CHCCHCCHCH33
OHOH
CHCH33
(73%)(73%)
Two of the groups Two of the groups attached to the attached to the tertiary carbon tertiary carbon come from the come from the Grignard reagentGrignard reagent
Dr. Wolf's CHM 201 & 202 14-53
Alkane Synthesis Using Alkane Synthesis Using Organocopper ReagentsOrganocopper Reagents
Dr. Wolf's CHM 201 & 202 14-54
Lithium dialkylcuprates are useful synthetic Lithium dialkylcuprates are useful synthetic reagents.reagents.
They are prepared from alkyllithiums and a They are prepared from alkyllithiums and a copper(I) halide.copper(I) halide.
2RLi + 2RLi + CuCuXX RR22CuCuLi + LiLi + LiXX
[customary solvents are diethyl ether and [customary solvents are diethyl ether and tetrahydrofuran (THF)]tetrahydrofuran (THF)]
Lithium DialkylcupratesLithium DialkylcupratesLithium DialkylcupratesLithium Dialkylcuprates
Dr. Wolf's CHM 201 & 202 14-55
the alkyllithium first reacts with the copper(I) the alkyllithium first reacts with the copper(I) halidehalide
How?How?How?How? RR LiLi
CuCu II
LiLi++RR
CuCu II––
Dr. Wolf's CHM 201 & 202 14-56
the alkyllithium first reacts with the copper(I) the alkyllithium first reacts with the copper(I) halidehalide
then a second molecule of the alkyllithium then a second molecule of the alkyllithium reacts with the alkylcopper species formed in reacts with the alkylcopper species formed in the first stepthe first step
LiLi++
––
How?How?How?How? RR LiLi
CuCu II
LiLi++RR
CuCu II––
RR LiLi
RR CuCu
RR
CuCuRR
Dr. Wolf's CHM 201 & 202 14-57
RR22CuCuLiLi ++ R'R'XX RR R'R' ++ RRCuCu ++ LiLiXX
ArAr22CuCuLiLi ++ R'R'XX ArAr R'R' ++ ArArCuCu ++ LiLiXX
Lithium diorganocuprates are used toLithium diorganocuprates are used toform C—C bondsform C—C bonds
Lithium diorganocuprates are used toLithium diorganocuprates are used toform C—C bondsform C—C bonds
Dr. Wolf's CHM 201 & 202 14-58
primary alkyl halides work best (secondary and primary alkyl halides work best (secondary and tertiary alkyl halides undergo elimination)tertiary alkyl halides undergo elimination)
diethyl etherdiethyl ether
(CH(CH33))22CuCuLiLi ++ CHCH33(CH(CH22))88CHCH22II
CHCH33(CH(CH22))88CHCH22CHCH33
(90%)(90%)
Example: Lithium Example: Lithium dimethyldimethylcupratecuprateExample: Lithium Example: Lithium dimethyldimethylcupratecuprate
Dr. Wolf's CHM 201 & 202 14-59
Example: Lithium Example: Lithium diphenyldiphenylcupratecuprateExample: Lithium Example: Lithium diphenyldiphenylcupratecuprate
diethyl etherdiethyl ether
(C(C66HH55))22CuCuLiLi ++ CHCH33(CH(CH22))66CHCH22II
CHCH33(CH(CH22))66CHCH22CC66HH55
(99%)(99%)
Dr. Wolf's CHM 201 & 202 14-60
(CH(CH33CHCH22CHCH22CHCH22))22CuLiCuLi
Vinylic halides can be usedVinylic halides can be usedVinylic halides can be usedVinylic halides can be used
++
diethyl etherdiethyl ether
BrBr
CHCH22CHCH22CHCH22CHCH33
(80%)(80%)
Dr. Wolf's CHM 201 & 202 14-61
(CH(CH33CHCH22CHCH22CHCH22))22CuLiCuLi
Aryl halides can be usedAryl halides can be usedAryl halides can be usedAryl halides can be used
++
diethyl etherdiethyl ether
II
CHCH22CHCH22CHCH22CHCH33
(75%)(75%)
Dr. Wolf's CHM 201 & 202 14-62
An Organozinc Reagent An Organozinc Reagent forfor
Cyclopropane SynthesisCyclopropane Synthesis
Dr. Wolf's CHM 201 & 202 14-63
Iodomethylzinc iodideIodomethylzinc iodideIodomethylzinc iodideIodomethylzinc iodide
reacts with alkenes to form cyclopropanesreacts with alkenes to form cyclopropanes
reaction with alkenes is called thereaction with alkenes is called theSimmons-Smith reactionSimmons-Smith reaction
CHCH22II22 + Zn + Zn ICHICH22ZnIZnICuCu
formed by reaction of diiodomethane withformed by reaction of diiodomethane withzinc that has been coated with copperzinc that has been coated with copper(called zinc-copper couple)(called zinc-copper couple)
Dr. Wolf's CHM 201 & 202 14-64
diethyl etherdiethyl ether
ExampleExampleExampleExample
HH22CC CC
CHCH22CHCH33
CHCH33
CHCH22II22, Zn/Cu, Zn/Cu CHCH22CHCH33
CHCH33
(79%)(79%)I CHI CH22 ZnI ZnI
via
Dr. Wolf's CHM 201 & 202 14-65
Stereospecific syn-additionStereospecific syn-additionStereospecific syn-additionStereospecific syn-addition
diethyl etherdiethyl etherCHCH22II22, Zn/Cu, Zn/Cu
CC CC
CHCH33CHCH22 CHCH22CHCH33
HH HH CHCH33CHCH22 CHCH22CHCH33
HH HH
Dr. Wolf's CHM 201 & 202 14-66
Stereospecific syn-additionStereospecific syn-additionStereospecific syn-additionStereospecific syn-addition
diethyl etherdiethyl etherCHCH22II22, Zn/Cu, Zn/Cu
CC CC
CHCH33CHCH22
CHCH22CHCH33HH
HH
CHCH33CHCH22
CHCH22CHCH33HH
HH
Dr. Wolf's CHM 201 & 202 14-67
Carbenes and CarbenoidsCarbenes and Carbenoids
Dr. Wolf's CHM 201 & 202 14-68
CarbeneCarbeneCarbeneCarbene
name to give to species that contains aname to give to species that contains adivalent carbon (carbon with two bondsdivalent carbon (carbon with two bondsand six electrons)and six electrons)
CC••••
BrBr BrBr
DibromocarbeneDibromocarbene
(same chemistry with dichlorocarbenes)(same chemistry with dichlorocarbenes)Carbenes are very reactive; normally cannot be isolated and Carbenes are very reactive; normally cannot be isolated and
stored.stored.Are intermediates in certain reactions.Are intermediates in certain reactions.
Dr. Wolf's CHM 201 & 202 14-69
Generation of DibromocarbeneGeneration of DibromocarbeneGeneration of DibromocarbeneGeneration of Dibromocarbene
CC
BrBr
BrBr
BrBr
HH ++ OC(CHOC(CH33))33
––
••••
••••••••
HH++ OC(CHOC(CH33))33••••
••••CC
BrBr
BrBr
BrBr
––••••
Dr. Wolf's CHM 201 & 202 14-70
Generation of DibromocarbeneGeneration of DibromocarbeneGeneration of DibromocarbeneGeneration of Dibromocarbene
++
CC
BrBr
BrBr
BrBr
––••••
CC••••
BrBr BrBr BrBr––
Dr. Wolf's CHM 201 & 202 14-71
Carbenes react with alkenesCarbenes react with alkenesto give cyclopropanesto give cyclopropanes
Carbenes react with alkenesCarbenes react with alkenesto give cyclopropanesto give cyclopropanes
+ CHBr+ CHBr33
BrBr
BrBr
(75%)(75%)
CBrCBr22 is an intermediate is an intermediate
stereospecific syn additionstereospecific syn addition
KOC(CHKOC(CH33))33
(CH(CH33))33COHCOH
End of Chapter 14