Organic Chemistry

PROBLEM 29

If the preference for formation of a six-membered ring were not so great, what other cyclic

product would be formed from the intramolecular aldol addition of

a. 2,6-heptanedione? b. 2,8-nonanedione?

PROBLEM 30

Can 2,4-pentanedione undergo an intramolecular aldol addition? If so, why? If not, why not?

PROBLEM 31 SOLVED

What products can be obtained if the following keto aldehyde is treated with a base?

Which would you expect to be the major product?

SOLUTION Three products are possible because there are three different sets of

More B and C are formed than A because a five-membered ring is formed in

preference to a seven-membered ring. The major product depends on the reaction condi-

tions. B is the thermodynamic product because it is formed from the more stable enolate. C

is the kinetic product because the of the aldehyde is more acidic than the

of the ketone (Table 19.1).

ABC

HO−

OO

CH 3 CCH 2 CH 2 CH 2 CH 2 CH

OO

CH 3 CCHCH− 2 CH 2 CH 2 CH

OO

CH 3 CCH 2 CH 2 CH 2 CHCH−

OO

CH− 2 CCH 2 CH 2 CH 2 CH 2 CH

O− O

CHCH 2 CH 2 CH 2 CH

O O−

CH 3 CCH 2 CH 2 CH 2 CH

O−

OH OH

O O

O

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

CCH 3

CH

CH 3

HO

O

HC

H 2 O

a-hydrogen

a-hydrogen

a-hydrogens.

O O

CH 3 CCH 2 CH 2 CH 2 CH 2 CH

HO−

H 2 O

O O

CH 3 CCH 2 CH 2 CH 2 CH 2 CH 2 CCH 3

2,8-nonanedione

a 1,7-diketone

CCH 3

O

HO−

H 2 O

O O

CH 3 CCH 2 CH 2 CH 2 CCH 3

2,6-heptanedione

a 1,5-diketone HO CH 3

O

HO CH 3

816 CHAPTER 19 Carbonyl Compounds III