Reaction Mechanism
The aliphatic carboxylate adds to the carbonyl carbon of Yamaguchi reagent, forming a mixed anhydride, which is then attacked by DMAP regioselectively at the less hindered carbon, producing acyl-substituted DMAP. It reacts with the alcohol to form the product ester.
The in situ formation of the symmetric aliphatic anhydride is proposed to explain the regioselectivity observed in the reactions of aliphatic acids, based on the fact that aliphatic carboxylates are more nucleophilic, and aliphatic anhydrides are more eletrophilic towards DMAP and alcohol than their counterparts.
Read more about this topic: Yamaguchi Esterification
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