A simple and mild esterification method using mixed carboxylic-carbonic anhydrides has been developed. Simple aliphatic carboxylic esters are prepared in high yields by the reaction of acids with equimolar amounts of chloroformates (2,2,2-trichloroethyl chloroformate is an exception) and triethylamine in the presence of a catalytic amount of 4-(dimethylamino)pyridine. Although aromatic acids give a mixture of the ester, the acid anhydride, and the carbonate under normal conditions utilized in this study, it is found that increasing the amount of 4-(dimethylamino)pyridine drastically decreases the formation of the acid anhydride and the carbonate, affording a satisfactory yield of the ester. This method reaches a limit with sterically hindered acids and the formation of the acid anhydride and the carbonate is favored.
Au(I)-catalyzed hydroacyloxylation of alkynes with carboxylic acids is described. PPh3AuCl/AgPF6 catalyst affords the Markonikov addition products, whereas PPh3AuCl/AgOTf catalyst gives the more stable isomerized products via the Markonikov products.
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