Synthesis of 5-acetoxy-2(5H)-furanones through manganese(III)-promoted functionalization of arylacetylenes

Reaction of phenylacetylenes la-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 alpha -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 alpha -alkyl vinyl radical intermediates 3g-h of undergoing oxidative cyclization. (C) 2000 Elsevier Science Ltd. All rights reserved.