25. Condensation Chemistry

Show how you would use an aldol, Claisen, or another type of condensation to make each compound.

(b)

Predict the major products of the following crossed Claisen condensations.

(a)

Predict the major products of the following crossed Claisen condensations.

(b)

Show what esters would undergo Claisen condensation to give the following β-keto esters.

(c)

Propose mechanisms for the following reactions.

(b)

Propose a mechanism for the self-condensation of methyl 3-phenylpropionate promoted by sodium methoxide.

Predict the products of the following Claisen condensations.

(c)

Ethoxide is used as the base in the condensation of ethyl acetate to avoid some unwanted side reactions. Show what side reactions would occur if the following bases were used.

(a) sodium methoxide

(b) sodium hydroxide

Esters with only one α hydrogen generally give poor yields in the Claisen condensation. Propose a mechanism for the Claisen condensation of ethyl isobutyrate, and explain why a poor yield is obtained.

Predict the products of self-condensation of the following esters.

(a) methyl propanoate + NaOCH₃

(b) ethyl phenylacetate + NaOCH2CH₃

Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.

(a)

(b)

Predict the products from crossed Claisen condensation of the following pairs of esters. Indicate which combinations are poor choices for crossed Claisen condensations.

(c)

(d)

Show how you would use an aldol, Claisen, or another type of condensation to make each compound.

(d)

Write the mechanism for the reaction of a 1,7-diester with an alkoxide ion to form a cyclic b-keto ester.

Draw the products of the following reactions:

d. diethyl 1,2-benzenedicarboxylate + sodium ethoxide: (1) slow addition of ethyl acetate; (2) HCl