FACTORS INFLUENCING THE REACTION-MODE SELECTIVITY AND REGIOCHEMISTRY OF INTERMOLECULAR PHOTOCYCLOADDITION REACTIONS OF ETHENES TO POLYSUBSTITUTED BENZENES

The photoreactions of the methylbenzonitriles; 2,3-, 2,4-, 2,6-, 3,4-, and 3,5- benzonitriles; and 2'- and 4'- methoxyacetophenones with cyc lopentene and ethyl vinyl ether have been investigated. Meta photocycl oaddition is the major process for the benzonitriles with cyclopentene , and regiochemical features reflect the influence of polar factors al ong the reaction pathway. The enol ether yields ortho cycloadducts exc lusively from all the benzenoid derivatives. The thermal ring opening of the primary photoadduct and the photolability of the cycloocta-1,3, 5-triene isomer depend markedly on the position of the substituents.