Synthetic photochemistry. Part 2. Generation of benzocyclobutenols by photocyclisation of benzocycloalkenones

Abstract

The irradiation of benzocycloalkenones (2) was examined in t-butyl alcohol and cyclisation into benzocyclobutenols (1) was observed for n= 7–9. On irradiation, substituted benzocycloalkenones (4) cyclised by an external mechanism to tricyclic benzocyclobutenols (7) and/or by an internal mechanism to alcohols (5) and/or (6), the relative ratio of these products depending on the nature of the alkyl substituent and the ring size. The results are related to the mechanism of the photoenolisation reaction.