Organic Chemistry

Section 8.8 The Diels–Alder Reaction: A 1,4-Addition Reaction 317

If the dienophile has two carbon–carbon double bonds, two successive Diels–Alder re-
actions can occur if excess diene is available.

PROBLEM 13

Give the products of each of the following reactions:

a.

b.

c.

d.

PROBLEM 14

Explain why the following are not optically active:

a. the product obtained from the reaction of 1,3-butadiene with cis-1,2-dichloroethene

b. the product obtained from the reaction of 1,3-butadiene with trans-1,2-dichloroethene

Predicting the Product when Both Reagents Are Unsymmetrically
Substituted
In each of the preceding Diels–Alder reactions, only one product is formed (ignoring
stereoisomers) because at least one of the reacting molecules is symmetrically substi-
tuted. If both the diene and the dienophile are unsymmetrically substituted, however,
two products are possible:

Two products are possible because the reactants can be aligned in two different ways.

+ or

OCH 3

CH

O

CH

CH 2

+

OCH 3

CH

O

CH

CH 2

O

O

CH 3 CCHCH CCH 3

CH 3 CH 3

+

CH 2 C C CH 2 O O O

CH 3 CH 3

+

CH 2 CH CH CH 2 + HC C C N

∆

CH 2 CH CH 2 + CH 3 C C C CCH 3

O O

CH

∆

O

O

+

O

O

O

O

20 ºC

5-methoxy-3-cyclohexene-

carbaldehyde

2-methoxy-3-cyclohexene-

carbaldehyde

O

CH

CH 2 CHCH CHOCH 3 CH 2 CHCH

O

+ +

CH 3 O O

CH

OCH 3

neither compound is symmetric