Photochemistry of cis-4,4-diphenyl-2-cyclohepten-1-one

• Published in: Journal of photochemistry and photobiology. A, Chemistry Chemistry, 1991-04, Vol.57 (1), p.317-329
• Main Authors: Bunce, Richard A., Taylor, Vicki L., Holt, Elizabeth M.
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics)
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/1010-6030(91)85026-D

The synthesis and photochemistry of 4,4-diphenyl-2-cyclohepten-1-one are reported. Despite the presence of phenyls at C-4, irradiation of the title compound affords only the [2+2] cycloaddition products; no phenyl-migration products normally associated with 4,4-diphenyl-2-cyclohexe-1-one photochemistry are observed. The structure and stereochemistry of the products have been unequivocally assigned by X-ray crystallographic methods as the trans-syn-trans (major) and the trans-anti-trans head-to-head dimers. The ratio of the products (2.4:1) is the same in tert-butyl alcohol and benzene. The current work provides the first definitive structural assignments for photochemically-derived cycloheptenone dimers. The mechanism can be rationalized in terms of a ground state asynchronous [ π2 s + π2 a] cycloaddition or a stepwise diradical-mediated addition of the intermediate trans-2-cycloheptenone species to a molecule of the cis enone.