Cyclization of alkynoic acids with gold catalysts: a surprising dichotomy between AuI and AuIII

ω-Acetylenic acids, substituted or not at their acetylenic end, could be efficiently cyclized to γ- or δ-alkylidene lactones in the presence of AuCl and K2CO3. In contrast AuCl3 led to lactone dimers, probably through cyclization and reductive dimerization. These AuI and AuIII catalyzed cyclizations were totally regioselective and most often highly stereoselective.