Synthesis of 5-Acetoxy-2(5H)-Furanones through Manganese(III)-Promoted Functionalization of Arylacetylenes

Reaction of phenylacetylenes 1a–e with manganese(III) triacetate in acetic acid/acetic anhydride at reflux gave the corresponding 5-acetoxy-5-phenyl-2(5H)-furanones 2a–e in good yield (40–86%). Furanones 2 were derived from further oxidation of the initially formed 5-phenyl-2(3H)-furanones 4 which were in turn obtained through regioselective addition of carboxymethyl radicals to the alkyne 1 triple bond and subsequent oxidative cyclization of the resulting α-phenylvinyl radical 3. In contrast, the (trimethylsilyl)alkylacetylene 1f gave the corresponding furanone 2f in only 25% yield, whereas alkylacetylenes 1g–h totally failed to give the corresponding furanones 2f–h, probably due to the incapability of the α-alkyl vinyl radical intermediates 3g–h of undergoing oxidative cyclization.