PHOTOCHEMICAL DECOMPOSITION OF BENZOCYCLOBUTENONE P-TOLUENESULFONYLHYDRAZONE

The photochemical decomposition of benzocyclobutenone p-toluenesulfony lhydrazone led to a wide variety of products including the E- and Z-is omers of l,1'-bi(benzocyclobutenylidene) 6a; cis-trans-benzocyclobuten ylidene trimer 7; cyclohepatrienes 8-10; benzocyclobutenone azine in i t's anti-anti (11), anti-syn (12), and syn-syn conformations (13); ant i- and syn-benzocyclobutenone N-benzocyclobutenyl-N-tosylhydrazone (14 and 15, respectively); (benzocyclobutenyl)hydrazine (16); benzocyclob utenyl p-tolyl sulfone (17); and benzocyclobutenone 1. Their isolation , identification and mechanism of formation are discussed. The data in dicate that while the addition of arylcarbenes to alkenes results in t he preferential formation of the more-hindered syn products, arylcarbe ne 5 adds to aryl olefins (styrenes and dimer 6) in a stereospecific a nti orientation to give the less-hindered product. In addition, the mi nimal steric effects observed in these systems presumably results from the 90 degrees angle of the cyclobutyl ring, which pulls the phenyl r ing back and thus minimizes its steric contribution.