Gold Catalysis: Oxepines from γ‐Alkynylfurans

A ketal group in a furyl position affords arene oxides from γ‐alkynylfurans even with the simple gold(III) chloride (AuCl 3 ) 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.