Organic Chemistry

810 CHAPTER 19 Carbonyl Compounds III

Ludwig Claisen (1851–1930)was
born in Germany and received a
Ph.D. from the University of Bonn,
studying under Kekulé. He was a
professor of chemistry at the
University of Bonn, Owens College
(Manchester, England), the
University of Munich, the University
of Aachen, the University of Kiel,
and the University of Berlin.

PROBLEM 21

Give the products obtained from mixed aldol additions of the following compounds:

a. c.

b. d.

PROBLEM 22

Describe how the following compounds could be prepared using an aldol addition in the

first step of the synthesis:

a. c.

b.

PROBLEM 23

Propose a mechanism for the following reaction:

19.14 The Claisen Condensation

When two molecules of an esterundergo a condensation reaction, the reaction is called

a Claisen condensation. The product of a Claisen condensation is a ester.

As in an aldol addition, in a Claisen condensation one molecule of carbonyl

compound is converted into an enolate when an is removed by a strong

base. The enolate attacks the carbonyl carbon of a second molecule of ester. The

base employed corresponds to the leaving group of the ester so that the reactant

is not changed if the base acts as a nucleophile and attacks the carbonyl group

(Section 19.10).

a-hydrogen

O

2 CH 3 CH 2 COCH 2 CH 3 CH 3 CH 2 C CHCOCH 2 CH 3 CH 3 CH 2 OH

O O

1. CH 3 CH 2 O


2. HCl

−

+

a -keto ester

CH 3

b-keto

CHCCH CH

O

CH

O

CH 3 CH 2 CCHCH 2 OH

O

CH 3

+ CH 3 CH 2 CH

O

HCH

excess

O

CH 3 CCH 3 +

O

CH 3 CH 2 CCH 2 CH 3

O

+ CH 3 CH 2 CH

O

O

CH 3 CH 2 CH 2 CH +

O

CH 3 CH 2 CH 2 CH 2 CH

O

3-D Molecule:

b-Keto ester

HO−

CH 2 CCH (^2) EtOH
C 6 H 5
C 6 H 5 C 6 H 5
C 6 H 5

• CC
  OOO
  O