大学有机化学课件14_11_15
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Are intermediates in certain reactions.
Generation of Dibromocarbene
Br – ••
Br C H + ••O••C(CH3)3 Br
Br Br C••–
Br
••
+ H O••C(CH3)3
Generation of Dibromocarbene
(CH3)2CuLi + CH3(CH2)8CH2I diethyl ether
CH3(CH2)8CH2CH3 (90%)
primary alkyl halides work best (secondary and tertiary alkyl halides undergo elimination)
reaction with alkenes is called the Simmons-Smith reaction
Example
CH2CH3 CH2I2, Zn/Cu
H2C
C CH3
diethyl ether
CH2CH3 CH3 (79%)
Stereospecific syn-addition
Iodomethylzinc iodide
formed by reaction of diiodomethane with zinc that has been coated with copper (called zinc-copper couple)
Cu CH2I2 + Zn
ICH2ZnI
reacts with alkenes to form cyclopropanes
CH2CH2CH2CH3 (80%)
Aryl halides can be used
(CH3CH2CH2CH2)2CuLi +
I
diethyl ether
CH2CH2CH2CH3 (75%)
14.12 An Organozinc Reagent
for Cyclopropane Synthesis
CH3CH2 C
H
CH2CH3 C
H
CH2I2, Zn/Cu diethyl ether
CH3CH2 H
CH2CH3 H
Stereospecific syn-addition
CH3CH2 C
H
H C
CH2CH3
CH2I2, Zn/Cu diethyl ether
CH3CH2 H
H CH2CH3
14.13 Carbenes and Carbenoids
14.11 Alkane Synthesis Using Organocopper Reagents
Lithium Dialkylcuprates
Lithium dialkylcuprates are useful synthetic reagents.
They are prepared from alkyllithiums and a copper(I) halide.
R Li+
Cu I
Cu I–
How?
the alkyllithium first reacts with the copper(I) halide
R Li
R Li+
Cu I
Cu I–
then a second molecule of the alkyllithium reacts with the alkylcopper species formed in the first step
18-Electron Rule
The number of ligands attached to a metal will be such that the sum of the electrons brought by the ligands plus the valence electrons of the metal equals 18.
Carbene
name to give to species that contains a divalent carbon (carbon with two bonds and six electrons)
••
C
Br
Br
dibromocarbene
Carbenes are very reactive; normally cannot be isolated and stored.
R Li
R Li+
R Cu
R Cu –
Lithium diorganocuprates are used to form C—C bonds
R2CuLi + R'X Ar2CuLi + R'X
R R' + RCu + LiX Ar R' + ArCu + LiX
Example: Lithium dimethylcuprate
2RLi + CuX
R2CuLi + LiX
[customary solvents are diethyl ether and tetrahydrofuran (THF)]
How?
the alkyllithium first reacts with the copper(I) halide
Βιβλιοθήκη Baidu
R Li
14.14 Transition-Metal Organic Compounds
Introduction
Many organometallic compounds derived from transition metals have useful properties. Typical transition metals are iron, nickel, chromium, platinum, and rhodium.
••
Br C Br + Br–
Br Br C••–
Br
Carbenes react with alkenes to give cyclopropanes
KOC(CH3)3
Br
+ CHBr3
(CH3)3COH
Br
(75%)
CBr2 is an intermediate stereospecific syn addition
Example: Lithium diphenylcuprate
(C6H5)2CuLi + CH3(CH2)6CH2I diethyl ether
CH3(CH2)6CH2C6H5 (99%)
Vinylic halides can be used
(CH3CH2CH2CH2)2CuLi +
Br
diethyl ether
Generation of Dibromocarbene
Br – ••
Br C H + ••O••C(CH3)3 Br
Br Br C••–
Br
••
+ H O••C(CH3)3
Generation of Dibromocarbene
(CH3)2CuLi + CH3(CH2)8CH2I diethyl ether
CH3(CH2)8CH2CH3 (90%)
primary alkyl halides work best (secondary and tertiary alkyl halides undergo elimination)
reaction with alkenes is called the Simmons-Smith reaction
Example
CH2CH3 CH2I2, Zn/Cu
H2C
C CH3
diethyl ether
CH2CH3 CH3 (79%)
Stereospecific syn-addition
Iodomethylzinc iodide
formed by reaction of diiodomethane with zinc that has been coated with copper (called zinc-copper couple)
Cu CH2I2 + Zn
ICH2ZnI
reacts with alkenes to form cyclopropanes
CH2CH2CH2CH3 (80%)
Aryl halides can be used
(CH3CH2CH2CH2)2CuLi +
I
diethyl ether
CH2CH2CH2CH3 (75%)
14.12 An Organozinc Reagent
for Cyclopropane Synthesis
CH3CH2 C
H
CH2CH3 C
H
CH2I2, Zn/Cu diethyl ether
CH3CH2 H
CH2CH3 H
Stereospecific syn-addition
CH3CH2 C
H
H C
CH2CH3
CH2I2, Zn/Cu diethyl ether
CH3CH2 H
H CH2CH3
14.13 Carbenes and Carbenoids
14.11 Alkane Synthesis Using Organocopper Reagents
Lithium Dialkylcuprates
Lithium dialkylcuprates are useful synthetic reagents.
They are prepared from alkyllithiums and a copper(I) halide.
R Li+
Cu I
Cu I–
How?
the alkyllithium first reacts with the copper(I) halide
R Li
R Li+
Cu I
Cu I–
then a second molecule of the alkyllithium reacts with the alkylcopper species formed in the first step
18-Electron Rule
The number of ligands attached to a metal will be such that the sum of the electrons brought by the ligands plus the valence electrons of the metal equals 18.
Carbene
name to give to species that contains a divalent carbon (carbon with two bonds and six electrons)
••
C
Br
Br
dibromocarbene
Carbenes are very reactive; normally cannot be isolated and stored.
R Li
R Li+
R Cu
R Cu –
Lithium diorganocuprates are used to form C—C bonds
R2CuLi + R'X Ar2CuLi + R'X
R R' + RCu + LiX Ar R' + ArCu + LiX
Example: Lithium dimethylcuprate
2RLi + CuX
R2CuLi + LiX
[customary solvents are diethyl ether and tetrahydrofuran (THF)]
How?
the alkyllithium first reacts with the copper(I) halide
Βιβλιοθήκη Baidu
R Li
14.14 Transition-Metal Organic Compounds
Introduction
Many organometallic compounds derived from transition metals have useful properties. Typical transition metals are iron, nickel, chromium, platinum, and rhodium.
••
Br C Br + Br–
Br Br C••–
Br
Carbenes react with alkenes to give cyclopropanes
KOC(CH3)3
Br
+ CHBr3
(CH3)3COH
Br
(75%)
CBr2 is an intermediate stereospecific syn addition
Example: Lithium diphenylcuprate
(C6H5)2CuLi + CH3(CH2)6CH2I diethyl ether
CH3(CH2)6CH2C6H5 (99%)
Vinylic halides can be used
(CH3CH2CH2CH2)2CuLi +
Br
diethyl ether