Arylcyclopropane photochemistry. Part 4. The photochemistry of some 2-arylcyclopropanecarboxylates

Abstract

The photochemistry of some 2-arylcyclopropanecarboxylates has been studied. Both the direct (λ 254 nm) and triplet-sensitized (λ 313 nm) irradiation of the trans-isomers yields only the corresponding cis-isomers. The direct irradiation of methyl cis-2-phenylcyclopropanecarboxylate and of cis-2-phenylcyclopropanecarboxylic acid yields products which are formed via 1,3-dipolar intermediates. The difference in photoreactivity between these cis-isomers and their trans-isomers is explained in terms of intramolecular exciplex formation with the cis-isomers which cannot occur with the trans-isomers. The difference in photoreactivity between the cis-compounds without a methoxy-group (2a,b) and those with a methoxy-group attached to the phenyl nucleus (2c,d) is explained in terms of the occurrence of a chemical reaction of the intramolecular exciplex of (2a,b) and the non-occurrence of any chemical reaction of the intramolecular exciplex of (2c,d). The intramolecular exciplex formation with the methoxy-substituted cis-compounds (2c,d) only leads to an increased ϕ_isc of these cis-compounds relative to that of the corresponding trans-isomers (1c,d).