14 11 alkane synthesis using organocopper reagents
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14.11 Alkane Synthesis Using Organocopper Reagents. Dr. Wolf\'s CHM 201 & 202. 14-53. Lithium Dialkylcuprates. Lithium dialkylcuprates are useful synthetic reagents. They are prepared from alkyllithiums and a copper(I) halide. 2RLi + Cu X. R 2 Cu Li + Li X.

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lithium dialkylcuprates
Lithium Dialkylcuprates

Lithium dialkylcuprates are useful synthetic reagents.

They are prepared from alkyllithiums and a copper(I) halide.

2RLi + CuX

R2CuLi + LiX

[customary solvents are diethyl ether and tetrahydrofuran (THF)]

Dr. Wolf\'s CHM 201 & 202

14-54

slide3

R

Li

R

Cu

Cu

I

How?

the alkyllithium first reacts with the copper(I) halide

Li+

I–

Dr. Wolf\'s CHM 201 & 202

14-55

slide4

R

Li

R

Cu

Cu

I

R

R

Li

R

Cu

R

Cu

How?

the alkyllithium first reacts with the copper(I) halide

Li+

I–

then a second molecule of the alkyllithium reacts with the alkylcopper species formed in the first step

Li+

Dr. Wolf\'s CHM 201 & 202

14-56

lithium diorganocuprates are used to form c c bonds

+

+

+

R\'X

LiX

R

R\'

RCu

R2CuLi

Lithium diorganocuprates are used toform C—C bonds

+

+

+

R\'X

LiX

Ar

R\'

ArCu

Ar2CuLi

Dr. Wolf\'s CHM 201 & 202

14-57

example lithium dimethyl cuprate
Example: Lithium dimethylcuprate

+

(CH3)2CuLi

CH3(CH2)8CH2I

primary alkyl halides work best (secondary and tertiary alkyl halides undergo elimination)

diethyl ether

CH3(CH2)8CH2CH3

(90%)

Dr. Wolf\'s CHM 201 & 202

14-58

example lithium diphenyl cuprate
Example: Lithium diphenylcuprate

+

(C6H5)2CuLi

CH3(CH2)6CH2I

diethyl ether

CH3(CH2)6CH2C6H5

(99%)

Dr. Wolf\'s CHM 201 & 202

14-59

vinylic halides can be used

CH2CH2CH2CH3

Vinylic halides can be used

+

Br

(CH3CH2CH2CH2)2CuLi

diethyl ether

(80%)

Dr. Wolf\'s CHM 201 & 202

14-60

aryl halides can be used
Aryl halides can be used

+

I

(CH3CH2CH2CH2)2CuLi

diethyl ether

CH2CH2CH2CH3

(75%)

Dr. Wolf\'s CHM 201 & 202

14-61

iodomethylzinc iodide
Iodomethylzinc iodide

formed by reaction of diiodomethane withzinc that has been coated with copper(called zinc-copper couple)

reacts with alkenes to form cyclopropanes

reaction with alkenes is called theSimmons-Smith reaction

Cu

CH2I2 + Zn

ICH2ZnI

Dr. Wolf\'s CHM 201 & 202

14-63

example
Example

CH2CH3

CH2CH3

CH2I2, Zn/Cu

H2C

C

CH3

diethyl ether

CH3

via

(79%)

I CH2 ZnI

Dr. Wolf\'s CHM 201 & 202

14-64

stereospecific syn addition

CH3CH2

CH2CH3

C

C

H

H

Stereospecific syn-addition

CH2I2, Zn/Cu

diethyl ether

CH3CH2

CH2CH3

H

H

Dr. Wolf\'s CHM 201 & 202

14-65

stereospecific syn addition1

C

C

Stereospecific syn-addition

CH3CH2

H

H

CH2CH3

CH2I2, Zn/Cu

diethyl ether

CH3CH2

H

H

CH2CH3

Dr. Wolf\'s CHM 201 & 202

14-66

14 13 carbenes and carbenoids
14.13Carbenes and Carbenoids

Dr. Wolf\'s CHM 201 & 202

14-67

carbene

••

C

Br

Br

Dibromocarbene

Carbene

name to give to species that contains adivalent carbon (carbon with two bondsand six electrons)

(same chemistry with dichlorocarbenes)

Carbenes are very reactive; normally cannot be isolated and stored.

Are intermediates in certain reactions.

Dr. Wolf\'s CHM 201 & 202

14-68

generation of dibromocarbene

••

OC(CH3)3

C

••

Br

H

Br

C

Br

Generation of Dibromocarbene

Br

+

Br

H

Br

••

+

OC(CH3)3

••

Dr. Wolf\'s CHM 201 & 202

14-69

generation of dibromocarbene1

Br

Br

Br

C

Br

Generation of Dibromocarbene

••

C

+

Br

Br

Dr. Wolf\'s CHM 201 & 202

14-70

carbenes react with alkenes to give cyclopropanes
Carbenes react with alkenesto give cyclopropanes

CBr2 is an intermediate

stereospecific syn addition

Br

KOC(CH3)3

+ CHBr3

(CH3)3COH

Br

(75%)

Dr. Wolf\'s CHM 201 & 202

14-71

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