Organic Chemistry

Section 19.15 The Mixed Claisen Condensation 813

Tutorial:

Claisen reactions—synthesis

A aldehyde is formed when a ketone condenses with a formate ester.

A ester is formed when a ketone condenses with diethyl carbonate.

PROBLEM 26

Give the product of each of the following reactions:

a.

b.

c.

d.

PROBLEM 27 SOLVED

Show how the following compounds could be prepared, starting with 3-cyanocyclohexanone:

a. b.

SOLUTION TO 27a Because the desired compound is a 1,3-dicarbonyl compound, it

can be prepared by treating an enolate with an ester.

O

CN

O

1. CH 3 CH 2 COCH 3

O

CH 3 O− −

2. H 3 O+

O O

CCH 2 CH 3

CN CN

O

O

CN

CH 2 CH 2 CCH 3

O O

CN

CCH 2 CH 3

1. CH 3 CH 2 O−

CH 3 CH 2 COCH 2 CH (^3) 2. HCl
O
CH 3 CH 2 OCOCH 2 CH 3 +
excess
O

1. CH 3 O−

CH 3 CH 2 CH 2 COCH (^3) 2. HCl
O
HCOCH 3 +
excess
O

1. CH 3 CH 2 O−


2. HCl

COCH 2 CH 3

O

+

excess

O

CCH 3

1. CH 3 O−

• CH 3 COCH (^3) 2. HCl
  O
  CH 3 CH 2 COCH 3
  O
  b-keto
  ethyl formate
  add slowly excess
  O
  ++HC OCH 2 CH 3 CH 3 CH 2 OH

1. CH 3 CH 2 O−


2. HCl

O O

O

CH

a -keto aldehyde

b-keto

diethyl carbonate
add slowly excess a -keto ester

O

++CH 3 CH 2 OC OCH 2 CH 3 CH 3 CH 2 OH

1. CH 3 CH 2 O−


2. HCl

O O

O

COCH 2 CH 3