Au(I)-Catalyzed Hydrative Rearrangement of 1,1-Diethynylcarbinol Acetates to Functionalized Cyclopentenones and Allenones

Atom-economical syntheses of isomeric 5-acetoxy-2-alkyl-2-cyclopentenones (2) and acetoxymethyl (x-alkylailen ones (3) have been described via Au-catalyzed hydrative rearrangement of 1,1-diethynyl-carbinol acetates (1). In anhydrous condition, Au(I)-catalyzed [3,3]-rearrangement of 1 afforded the 3-alkynylallenyl acetate 4 in low yield. Treatment of 1 with Au(I) catalyst in wet CH2Cl2 produced either 2 or 3 as a major product depending on the temperature, reaction time. and catalyst loading. D has been proposed as an intermediate, which might be formed via Au(I)-induced internal oxacyclization of the intermediate 4 followed by chemoselective nucleophilic attack by the water molecule. Formation of 2 or 3 might be explained via sequential 1,3-dioxole ring opening and gold-promoted 5-endo-dig carbocyclization or simple protonation of the intermediate D, respectively.