Photoreactions of several arylalkylcyclopropenethiones (lb-e) have been investigated. The products formed have been rationalized on the basis of a-cleavage as the primary photoprocess. The photochemical a-cleavage is presumed to originate from the lowest excited nr* triplet state. A regioselective a-cleavage reaction has been observed and this unusual regioselectivity is explained on the basis of close approach of the ground-state energy surface of the ...
