Photochemical Decomposition of Benzocyclobutenone p-Toluenesulfonylhydrazone

The photochemical decomposition of benzocyclobutenone p-toluenesulfonylhydrazone led to a wide variety of products including the E-and Z-isomers of 1,1′-bi(benzocyclobutenylidene) 6a; cis-transbenzocyclobutenylidene trimer 7; cyclohepatrienes 8–10; benzocyclobutenone azine in it's anti-anti (11), anti-syn (12), and syn-syn conformations (13); anti-and syn-benzocyclobutenone N-benzocyclobutenyl-N-tosylhydrazone (14 and 15, respectively); (benzocyclobutenyl)hydrazine (16); benzocyclobutenyl p-tolyl sulfone (17); and benzocyclobutenone 1. Their isolation, identification and mechanism of formation are discussed. The data indicate that while the addition of arylcarbenes to alkenes results in the preferential formation of the more-hindered syn products, arylcarbene 5 adds to aryl olefins (styrenes and dimer 6) in a stereospecific anti orientation to give the less-hindered product. In addition, the minimal steric effects observed in these systems presumably results from the 90° angle of the cyclobutyl ring, which pulls the phenyl ring back and thus minimizes its steric contribution.