Organic Chemistry

Now continue on to Problem 14.

PROBLEM 14

How could each of the following compounds be prepared from a ketone and an alkyl

halide?

19.9 Alkylation and Acylation of the -Carbon via

an Enamine Intermediate

We have seen that an enamine is formed when an aldehyde or a ketone reacts with a

secondary amine (Section 18.6).

Enamines react with electrophiles in the same way that enolates do.

N

E+

N+

enamine enolate

O−

E+

O

EE

O

++H 2 O

N

H

N

enamine

catalytic

H+

pyrrolidine

secondary amine

A

O

CH 2 CHCCH 2 CH 3

CH 3

O

a. CH 3 CCH 2 CH 2 CH CH 2 b.

802 CHAPTER 19 Carbonyl Compounds III

CH 3 CH 2 CCH 2 CH 3

O

3-pentanone

CH 3 CH 2 CCH 2 CH 2 CH 3

O

CH 3 CH 2 CCHCH 3

O

CH 3 CH 2 CCHCH 2 CH 3

O

3-hexanone

LDA CH 3 CH 2 Br

LDA

CH 3 Br CH 3 Br

− CH^3 CH^2 CCHCH^3

O

− CH^3 CHCCH^2 CH^2 CH^3

O

+ −

CH 3 CH 2 CCHCH 2 CH 3

O

CH 3 CHCCH 2 CH 2 CH 3

O

+

CH 2 CH 3

4-methyl-3-hexanone

CH 3

4-methyl-3-hexanone

CH 3

2-methyl-3-hexanone