A synthetic approach to azepin-4-ones exploiting azide photolysis in low-temperature matrices

Photolysis of 2,6-dichloro-4-azidophenol and 2,6-dibromo-4-azidophenol in N2 or Ar matrices at 12–14 K results in ring expansion, yielding in each case either the corresponding hydroxydidehydroazepine or, in more concentrated matrices, the tautomeric azepin-4-one.