||Chapter 21: Ester Enolates
of b-carbonyl esters
Reaction type: Hydrolysis then
- Loss of carbon dioxide is called
- Esters or carboxylic acids
with a carbonyl group at the 3- (or b-) position
readily undergo thermal decarboxylation.
- Decarboxylation was first encountered
in Chapter 19 for carboxylic acids (review).
- The reactive species is the carboxylic
acid or the carboxylate anion.
- So the ester must first be converted
to the acid by hydrolysis (review)
- The decarboxylation reaction
then proceeds via a cyclic transition state giving an enol intermediate that
tautomerises to the carbonyl.
DECARBOXYLATION OF A b-KETOACID
Remember curly arrows flow.... Start at the protonation of the carbonyl,
break the O-H bond and form the p
bond, break the C-C and make the C=C. Note the concerted
nature of this reaction and the cyclic transition state.