PHOTOSENSITIZED FRAGMENTATION OF A BICYCLO[4.2.0]OCTA-2,4-DIENE DERIVATIVE - PREPARATION OF ISOMERIC 1,2-DIACETOXYETHYLENES

Photosensitized reactions of trans-7,8-diacetoxybicyclo[4.2.0]octa-2,4-diene (1) lead to the isomeric diacetoxyethylenes and benzene in good yield and to a cycloadduct dimer of 1 as a minor product. The results contrast sharply with the results of direct irradiation of 1. Both cis and trans isomers of diacetoxyethylene are formed as primary products, though 1 is known to be cleanly a trans compound. Mechanisms which will account for the stereochemical result are discussed; one possibility is the fragmentation of triplet 1 to benzene and triplet diacetoxyethylene, a reaction of theoretical significance. © 1969, American Chemical Society. All rights reserved.