Gold catalysis:: Oxepines from γ-alkynylfurans

A ketal group in a furyl position affords arene oxides from gamma-alkynylfurans even with the simple gold(III) chloride (AuCl3) catalyst. These can either undergo Diels-Alder reactions, isomerise to stable oxepines by an oxygen-walk reaction or by the addition of water selectively be converted to phenols which differ in the position of the hydroxy group from the normal phenols formed in the gold-catalysed phenol synthesis. With a phenyl substituent on the furan, the 2-hydroxymethylpyridinato-gold(III) complex, not the usual arene oxide but an oxepine is obtained, still the arene oxide can be trapped from the valence-tautomeric equilibrium by a Diels-Alder reaction.