Organic Chemistry

866 CHAPTER 20 More About Oxidation–Reduction Reactions

The reaction of pentanal with butyl magnesium bromide forms the target compound.

PROBLEM 28

a. How could you synthesize the following compound from starting materials containing

no more than four carbons? (Hint:A 1,6-diketone can be synthesized by oxidative

cleavage of a 1,2-disubstituted cyclohexene.)

b. How could you synthesize the same compound in two steps from starting materials con-

taining no more than six carbons?

20.9 Oxidative Cleavage of Alkynes

The same reagents that oxidize alkenes also oxidize alkynes. Alkynes are oxidized to

diketones by a basic solution of at room temperature and are cleaved by

ozonolysis to carboxylic acids. Ozonolysis requires neither oxidative nor reductive

work-up—it is followed only by hydrolysis. Carbon dioxide is obtained from the CH

group of a terminal alkyne.

PROBLEM 29

What is the structure of the alkyne that gives each of the following sets of products upon

ozonolysis followed by hydrolysis?

a. b. + 2

O O

OH

O

HO OH

+ CO 2

COOH

O

+

CH 3 C CCH 2 CH 3 CH 3 C

O

CCH 2 CH 3

KMnO 4

HO−

O

CH 3 C CCH 2 CH 3 CH 3 COH

O

CH 3 CH 2 COH

CH 3 CH 2 CH 2 CCH + CO 2

O

CH 3 CH 2 CH 2 COH

1. O3, – 78 °C


2. H 2 O


3. O3, – 78 °C


4. H 2 O

2-pentyne

2-pentyne

1-pentyne

KMnO 4

O

O

OH O

O OH

1. O3, – 78 °C


2. Zn, H 2 O

H 2

Raney Ni

HBr Br Mg

Et 2 O MgBr

1. BH 3 /THF


2. HO−, H 2 O 2

PCC

O H 3 O+

MgBr

O− OH

+

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