5244

Using the bond energy table below, calculate ∆H° for the decarboxylation of a carboxylic acid:

Bond	∆H° (Kcal mole^–1)
C=O (in CO2)	192
C=O	179
C–C	83
C–H	99
O–H	111
C–O	86

Explain, using structures and words, why this reaction occurs commonly with b-ketoacids, but not with simple carboxylic acids.

5245

Indicate how the following experimental results support the proposed mechanism for the Claisen condensation of esters.

(a) When optically active methyl 2-phenylpropanoate is treated with potassium methoxide in methanol, the ester racemizes more rapidly than condensation occurs.

(b) When ethyl acetate reacts with sodium ethoxide in ethanol-OD, deuterium accumulates in the ethyl acetate more rapidly than Claisen condensation takes

5361

Suggest a synthetic sequence for the preparation of each of the following compounds beginning with ethyl acetoacetate or diethyl malonate and any other organic compounds with five or fewer carbon atoms.

(a)

(b)

(c)

5362

Suggest a sequence for the synthesis of the following compound from the indicated starting material and any other necessary reagents.