An Alternative Approach to Aldol Reactions: Gold-Catalyzed Formation of Boron Enolates from Alkynes

A new method for enolate generation via the gold-catalyzed addition of boronic acids to alkynes is reported. The formation of boron enolates from readily accessible ortho-alkynylbenzeneboronic acids proceeds rapidly with 2 mol % PPh3AuNTf2 at ambient temperature. The enolates undergo aldol reaction with an aldehyde present in the reaction mixture to give cyclic boronate esters, which can be subsequently transformed into phenols, biaryls, or dihydrobenzofurans via oxidation, Suzuki-Miyaura, or intramolecular Chan-Lam coupling, respectively. A combined gold/boronic acid catalyzed aldol condensation reaction of an alkynyl aldehyde was also successfully achieved.