Organic Chemistry

316 CHAPTER 8 Reactions of Dienes • Ultraviolet and Visible Spectroscopy

if the substituents in the dienophileare cis, they will be cis in the product; if the sub-

stituents in the dienophileare trans, they will be trans in the product.

The substituents in the dienewill also maintain their relative configurations in the

products. Notice that compounds containing carbon–carbon triple bonds can also be

used as dienophiles in Diels–Alder reactions to prepare compounds with two isolated

double bonds.

Each of the four previous reactions forms a product with two new asymmetric carbons.

Thus, each product has four stereoisomers. Because only syn addition occurs, each re-

action forms only two of the stereoisomers (Section 5.19). The Diels–Alder reaction is

stereospecific—the configuration of the reactants is maintained during the course of

the reaction—because the reaction is concerted. The stereochemistry of the reaction

will be discussed in more detail in Section 29.4.

A wide variety of cyclic compounds can be obtained by varying the structures of

the conjugated diene and the dienophile.

+

CO 2 CH 3

CO 2 CH 3

C

C

H

∆

CH 3 CH 3

CH 3 CH 3

O

O

+ O

O

O

O

20 ºC

CH 3

CH 3

H 3 C

H 3 C

COOH

COOH

HOOC

++

C

C

H

cis dienophile

∆

cis products

H

∆

CH 3

H 3 C

COOH

COOH

HOOC

++

C

C

H

trans dienophile trans products

H

CH 3 CH O

O

O

O

O

O

O

O

C

C

CH

CH

CH

CH 2 CH 3

H

H

HCH 3

HCH 2 CH 3

CH 3 H

CH 3 CH 2 H

CH 3 H

HCH 2 CH 3

HCH 3

CH 3 CH 2 H

CH 3

CH 2 CH 3

+

++

CH

C

C

CH

CH

CH

O

O

O

O

CH

CH

CH

CH

H +

H

∆

∆