The photochemical behaviour of 2-methylcyclohept-2-enones

Abstract

An efficient dimerisation of 1,3-dimethyl-8-oxabicyclo[5.3.0]dec-3-ene-2,9-dione 4 has been discovered, and probably involves an initial photo-induced formation of the transcyclohept-2-enone which then undergoes thermal dimerisation. Irradiation of the complex cycloheptenone, 1,3,10-trimethyl-8-oxabicyclo[5.3.0]dec-3-ene-2,9-dione 1 provided an 85% yield of a novel tricycle (and no dimer), tentatively identified as 1,8,10-trimethyl-3-oxatricyclo[6.2.0.0^4,10]decane-2,9-dione.