Photochemistry of benzotricyclo[3.2.0.02,7]heptene: Singlet excited state reactions derived from cyclopropane ring clevage
✍ Scribed by Richard P. Johnson; Katherine Schlimgen Davis
- Publisher
- Elsevier Science
- Year
- 1981
- Tongue
- French
- Weight
- 204 KB
- Volume
- 22
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
Q~t~e.ot -LW&&LCOM of, the ,I?LL?A hydhocatlbon in cycLohexane addo& P-uinyfindene ~onowxtadi~n~ M major ~JL&WLY photopkodueti . Q~tiehiwn .tab&Lng iA uned to de.btwune heaction mechatimn. It was recently reported* that direct irradiation of the title hydrocarbon (1) at 254 nm in methanol or hexane yields benzonorcaradiene (2), benzonorbornadiene (2) and two unidentified products presumed to be isomeric benzotropilidenes 2 and 5 as primary photoproducts. We describe here our own studies4 on the photochemistry of l_, which are significantly at variance with these results. 1 2 3 A 5 Our interest in the photochemistry of l_ was stimulated by the earlier observation of Edman that prolonged direct irradiation of benzonorbornadiene yielded a long-wavelength absorbing substance, suggested to be 3,4_benzotropilidene (4). In reinvestigating this question, we observed6 that benzonorbornadiene was slowly converted to 1, which subsequently underwent more rapid secondary and tertiary photoreaction. Direct irradiation of pure 1 in cyclohexane was then investigated; this afforded at low conversion, two major photoproducts (ratio ~a. 1.5:1) readily characterized as 2-vinylindene (5) and benzonorcaradiene (2), as well as several very minor products.' Careful examination of product mixtures and isolated