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

omega-Acetylenic acids, Substituted or not at their acetylenic end, could be efficiently cyclized to gamma- or delta-alkylidene lactones in the presence of AuCl and K2CO3. In contrast AuCl3 led to lactone dimers, probably through cyclization and reductive dimerization. These Au-I and Au-III catalyzed cyclizations were totally regioselective and most often highly stereoselective. (C) 2008 Elsevier Ltd. All rights reserved.