SOLUTION TO 27b Because the desired compound is a 1,5-dicarbonyl compound, it
can be prepared by a Michael reaction—treating an enolate with an
carbonyl compound.19.16 Intramolecular Condensation
and Addition Reactions
We have seen that if a compound has two functional groups that can react with each
other, an intramolecular reaction readily occurs if the reaction leads to the formation
of five- or six-membered rings (Section 11.11). Consequently, if base is added to a
compound that contains two carbonyl groups, an intramolecular reaction occurs if a
product with a five- or six-membered ring can be formed. Thus, a compound with two
ester groups undergoes an intramolecular Claisen condensation, and a compound with
two aldehyde or ketone groups undergoes an intramolecular aldol addition.Intramolecular Claisen Condensations
The addition of base to a 1,6-diester causes the diester to undergo an intramolecular
Claisen condensation, thereby forming a five-membered ring ester. An in-
tramolecular Claisen condensation is called a Dieckmann condensation.A six-membered ring ester is formed from a Dieckmann condensation of a
1,7-diester.The mechanism of the Dieckmann condensation is the same as the mechanism of
the Claisen condensation. The only difference between the two reactions is that the at-
tacking enolate and the carbonyl group undergoing nucleophilic attack are in different
molecules in the Claisen condensation, but are in the same molecule in the Dieckmann
condensation. The Dieckmann condensation, like the Claisen condensation, is drivena -keto ester- CH 3 O−
- HCl
CH 2
+ CH 3 OHOOOCH 2 CH 2 COCH 3a 1,7-diesterCH 2OCH 2 COCH 3COCH 3b-ketoa -keto ester- CH 3 O−
- HCl
a 1,6-diesterCH 2 + CH 3 OHOOOOCH 2 CH 2CH 2 COCH 3COCH 3 COCH 3b-ketoa,b-unsaturated814 CHAPTER 19 Carbonyl Compounds III
OOCH 2 CHCCH 3
CH 3 OHO
CH 3 O− −O O
CH 2 CH 2 CCH 3CN CN CNWalter Dieckmann (1869–1925)
was born in Germany. He received a
Ph.D. from the University of Munich
and became a professor of chemistry
there.