Palladium-catalyzed decarboxylative gem-selective addition of alkynoic acids to terminal alkynes

The regioselective palladium-catalyzed decarboxylative head-to-tail addition of alkynoic acid derivatives to terminal alkynes furnished gem-1,3-enynes. Both aryl- and alkyl-substituted alkynoic acids showed favorable reactivity and high selectivity. The proposed method provided good yields and showed broad functional group tolerance. In addition, the reaction of alkynoic acids with propiolic acid provided the corresponding gem-1,3-enynes via double decarboxylation. This is the first example of propiolic acid being employed as an acetylene surrogate for the formation of gem-1,3-enynes. Density functional theory calculations were conducted to rationalize the high selectivity observed in the formation of head-to-tail addition products.