The photochemical reaction of benzene with ethylenes: studies with allyl compounds, enamines, vinyl sulphide, and 5,6-dichlorobicyclo[2.2.1]hept-2-ene

Abstract

Benzene undergoes regio- and stereo-selective meta photocycloaddition to methyl but-3-enoate and pent-1-en-4-ol but methyl allyl ketone and NN-dimethylallylamine yield only products of the addend : likewise irradiation of benzene with enamines or methyl vinyl sulphide at 254 nm does not yield photoadducts. The meta photocycloadducts of benzene with methyl but-3-enoate and vinyl acetate and the ketones obtained by oxidation of the adducts from pent-1-en-4-ol are all essentially photostable and do not undergo Norrish Type II eliminations. The dechlorination products of the meta photocycloaddition of 5,6-trans-dichlorobicyclo[2.2.1]hept-2-ene and benzene undergo a retro-Diels-Alder addition at high temperatures, but the C₈H₈ isomer formed is cyclo-octatetraene.