Organic Chemistry Fifth Edition

1
Organic Chemistry II (Chem 234)Professor Duncan
J. Wardrop
Spring 2004
University of Illinois at Chicago
2
http//www.chem.uic.edu/wardrop/teaching/chem234/
Office Hour - SES 4446, Thursday, 3-4 p.m.
3
Chapter 14Organometallic Compounds
4
14.6Synthesis of Alcohols Using Grignard
Reagents
5
Grignard reagents react with

• formaldehyde to give primary alcohols
• aldehydes to give secondary alcohols
• ketones to give tertiary alcohols

6
Grignard reagents react with ketones
?
7
Example
8
14.7Synthesis of AlcoholsUsing Organolithium
Reagents

• Organolithium reagents react with aldehydes and
  ketones in the same way that Grignard reagents
  do.

9
Example

1. diethyl ether 2. H3O
Allylic Alcohol
(76)
10
14.8Synthesis of Propargylic Alcohols
11
(No Transcript)
12
Using Sodium Salts of Acetylenes
NaNH2
NH3
13
Using Acetylenic Grignard Reagents

CH3CH2MgBr
diethyl ether

CH3CH3
14
(No Transcript)
15
(No Transcript)
16
14.9Retrosynthetic Analysis

• Retrosynthetic analysis is the process by which
  we plan a synthesis by reasoning backward from
  the desired product (the "target molecule").

17
Retrosynthetic Analysis of Alcohols

• Step 1 Locate the carbon that bears the
  hydroxyl group.

18
Retrosynthetic Analysis of Alcohols

• Step 2 Disconnect one of the groups attached to
  this carbon.

19
Retrosynthetic Analysis of Alcohols
OH
20
Retrosynthetic Analysis of Alcohols

• What remains is the combination of Grignard
  reagent and carbonyl compound that can be used to
  prepare the alcohol.

21
Example

• There are two other possibilities. Can you see
  them?

CH3MgX
22
Synthesis
Mg, diethyl ether
CH3Br
CH3MgBr
1.
2. H3O
23
14.10Preparation of Tertiary AlcoholsFrom
Esters and Grignard Reagents
24
Grignard reagents react with esters
R'
R'
?
?
C

MgX
O

• but species formed is unstable and dissociates
  under the reaction conditions to form a ketone

25
Grignard reagents react with esters
R'
R'
?
?
C

MgX
O



CH3OMgX

• this ketone then goes on to react with a second
  mole of the Grignard reagent to give a tertiary
  alcohol

26
Example

2 CH3MgBr
1. diethyl ether 2. H3O

• Two of the groups attached to the tertiary
  carbon come from the Grignard reagent

OH
(CH3)2CHCCH3
CH3
(73)
27
14.11Alkane Synthesis Using Organocopper
Reagents
28
Lithium Dialkylcuprates

• Lithium dialkylcuprates are useful synthetic
  reagents.
• They are prepared from alkyllithiums and a
  copper(I) halide.

29
How?

• the alkyllithium first reacts with the copper(I)
  halide

Li
I
30
Lithium diorganocuprates are used toform CC
bonds



R'X
Ar
R'
ArCu
LiX
Ar2CuLi
31
Example Lithium dimethylcuprate

(CH3)2CuLi
CH3(CH2)8CH2I
diethyl ether
CH3(CH2)8CH2CH3
(90)

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

32
Example Lithium diphenylcuprate

(C6H5)2CuLi
CH3(CH2)6CH2I
diethyl ether
CH3(CH2)6CH2C6H5
(99)
33
Vinylic halides can be used

Br
(CH3CH2CH2CH2)2CuLi
diethyl ether
(80)
34
Aryl halides can be used

I
(CH3CH2CH2CH2)2CuLi
diethyl ether
CH2CH2CH2CH3
(75)
35
14.13Carbenes and Carbenoids
36
Carbene
name to give to species that contains adivalent
carbon (carbon with two bondsand six electrons)

• Carbenes are very reactive normally cannot be
  isolated and stored.
• Are intermediates in certain reactions.

37
Generation of Dibromocarbene
Br

Br
H
Br
38
Generation of Dibromocarbene

C


Br
Br
Br
39
Carbenes react with alkenesto give cyclopropanes
Br
KOC(CH3)3
CHBr3
(CH3)3COH
Br

• CBr2 is a highly reactive (shortlived)
  intermediate

(75)
40
Why the synthesis ofcyclopropanes is important?
Chrysanthemum cinerariaefolium
41
Why the synthesis ofcyclopropanes is important?
42
14.12An Organozinc Reagent forCyclopropane
Synthesis
43
Iodomethylzinc iodide
Cu
CH2I2 Zn
ICH2ZnI
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

44
Example
CH2CH3
CH2CH3
CH2I2, Zn/Cu
H2C
C
CH3
diethyl ether
CH3
(79)
45
Stereospecific syn-addition
CH2I2, Zn/Cu
diethyl ether
46
Stereospecific syn-addition
CH3CH2
H
H
CH2CH3
47
Suggested Problems 14.14, 14.16-14.23,
14.29-14.31, 14.34 Please Note Chapter 14.14 and
14.15 are not examinable -------------------------
---------------------------- Office Hour Now,
SES 4446