Recent work from this laboratory168 has shown that bi-cyclic hydrocarbons such as I which incorporate a cyclopropane ring, on irradiation in pentane solution at 185 nm (=6.7 eV), decompose according to eq 1 to give products(formula ommitted) which formally correspond to the cleavage of one or two bonds of the cyclopropane ring. These reactions are believed to occur from an electronically excited singlet state of the cyclopropane ring. Although the two-bond cleavage of cyclopropanes in gas-phase photolysis at wavelengths >185 nm is well-documented2, only a single example13, of a disubstituted cyclopropane which is capable of giving stereochemical information on the photoprocess has hitherto been reported. This work will be referred to later. © 1979, American Chemical Society. All rights reserved.