Photochemical ring opening of 7-benzoyl- and 7-methoxycarbonyldibenzonorcaradienes. competing 1,2-hydrogen shift and cyclization reactions of 1,3-diradicals.
[see reaction]. The UV irradiation of dibenzonorcaradienes bearing an acyl or alkoxycarbonyl substituent in the 7-position results in formation of substituted phenanthrenes, as well as cis-trans isomerization of the starting material. This reaction apparently proceeds via intermediate formation of a short-lived (tau = 1-20 ns) 1,3-diradical, which is produced by photochemical cleavage of one cyclopropane bond, while no evidence of alpha-carbonylcarbene formation was found.
Bogdanova
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Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, USA.
Popik
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