Photochemical transformations. 39. Effects of ring substituents and leaving groups on photo-Wagner-Meerwein rearrangements and their ground-state analogs
| Autor: | Ellen O. Aeling, Stanley J. Cristol |
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| Rok vydání: | 1985 |
| Předmět: | |
| Zdroj: | The Journal of Organic Chemistry. 50:2698-2707 |
| ISSN: | 1520-6904 0022-3263 |
| DOI: | 10.1021/jo00215a021 |
| Popis: | A variety of diarobicyclo(2.2.2)octa-2,5-dienes, substituted on the saturated bridge at C-7 or disubstituted at C-7 and C-8, have been subjected to direct irradiation in acetic acid, as well as to ground-state solvolysis. The ground-state reactions proceed as anticipated, occurring with preferred loss of the nucleofuge anti to the better participating ring, or with loss of the better nucleofuge, and with clean anti Wagner-Meerwein rearrangement to the diarobicyclo(3.2.1)octadienyl system, with one exception. The photoreactions proceed with reaction at the more readily reduced carbon-nucleofuge bond (chloride loss rather than methanesulfonate) with the dibenzo system. The (methylsulfonyl)oxy group is photoinert with both benzo rings unsubstituted but is photoactive with the better electron-donating veratrolo ring. The photo-Wagner-Meerwein rearrangements and photosolvolyses all proceed with preponderant or stereospecific syn migration, in contrast to the ground-state reactions. The photoreactivities are consistent with the requirement that electron transfer of an excited ..pi..* electron to the sigma/sup */ orbital of the carbon-nucleofuge bond must occur faster than electron-demotion processes occur. The stereochemical results are accommodated by the assumption that the resulting zwitterionic biradical has two possible competing fates leading to products. One involves loss of nucleofuge concerted with a syn 1,2-migration, and the other is a nonconcerted process inmore » which loss of nucleofuge results in formation of a biradical cation, which is non-stereospecific in its ultimate rearrangement. 30 references, 10 figures.« less |
| Databáze: | OpenAIRE |
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