Photolytic rearrangements in triphenylcyclopropene systems

Abstract

Photolysis of 1,2,3-triphenylcyclopropene results in dimerization to 1,2,3,4,5,6-hexaphenyltricyclo[3.1.0.0^2,4]-hexane. Photolysis of 3-phenyl-, 3-benzyl-, 3-methyl-, and 3-methoxy-1,2,3-triphenylcyclopropene yields no dimeric products. All the compounds rearrange to give some of the corresponding 3-substituted 1,2-diphenylindenes. In addition to indene formation, the 3-methoxy-compound undergoes fragmentation and the 3-benzyl-compound undergoes a benzyl proton shift to form 1,2,3,4-tetraphenylbutadiene isomers. The reaction is postulated to proceed by initial excitement of the cyclopropene π bond to a π diradical followed by ring opening of the cyclopropene to form a phenyl vinyl carbene which inserts into the 3-phenyl group to form the indene and may undergo other reactions where possible.