Mechanistic and synthetic aspects of the photochemistry of spiro-oxaziridines

The photo-rearrangements of certain spiro-oxaziridines derived from tetral-1-one have been investigated in order to establish the effect of competition between aryl and alkyl migration and to examine the photochemistry of these systems when the N-substituent suffers steric compression. A range of spiro-oxaziridines having the N-substituent in the syn-aryl or anti-aryl configuration have been converted to the corresponding lactams, either as mixtures of regio-isomers or single substances. It has been demonstrated that stereo-electronically controlled photo-rearrangements (migration of the bond anti- to the lone-pair of electrons on the nitrogen atom) occur when the N-substituent is anti- to the aromatic ring. Reduced regio-specificity of the photo-rearrangement of syn-spiro-oxaziridines suggests that the first formed N–O bond cleaved species has a significant lifetime. The synthetic utility of the photo-rearrangement of the anti-aryl oxaziridine has been demonstrated by the preparation of a range of tricyclic, heterocyclic compounds, including pyrrolo-benzazepinones, pyrrolo-isoquinolinones and azeto-benzazepinones. The photo-products may have potential pharmacological activity.