Organic Chemistry

carbonyl compounds are also useful to synthetic chemists because

once a bromine has been introduced into the of a carbonyl compound,

an carbonyl compound can be prepared by means of an E2 elimina-

tion reaction, using a strong and bulky base to encourage elimination over substitution

(Section 11.8).

PROBLEM 9

How would you prepare the following compounds from the given starting materials?

PROBLEM 10

How could the following compounds be prepared from a carbonyl compound with no

carbon–carbon double bonds?

PROBLEM 11

How could the following compounds be prepared from cyclohexanone?

19.7 Using LDA to Form an Enolate

The amount of carbonyl compound converted to enolate depends on the of the

carbonyl compound and the particular base used to remove the For

example, when hydroxide ion (the of its conjugate acid is 15.7) is used to remove

an a-hydrogenfrom cyclohexanone 1 pKa= 172 ,only a small amount of the carbonyl

pKa

a-hydrogen.

pKa

d.

O

CH 3

b.

O

CN

c.

O

SCH 3

a.

O

CN

O

CH 3

b. CCHCH^2

O

a. CH 3 CH CHCCH 2 CH 2 CH 3

d.

O

O

O

b. CH 3 CH 2 CH

O

CH 3 CHCH

O

OH

c.

O O

OCH 3

a. CH 3 CH 2 CH

O

CH 3 CHCH

O

N(CH 3 ) 2

tert-BuO−

tert-BuOH

O O

an , -unsaturated

carbonyl compound

Br

+ Br−

a,b-unsaturated

a-position

a-Brominated

798 CHAPTER 19 Carbonyl Compounds III