Cascade Radical Cyclizations via Biradicals Generated from (Z)-1,2,4-Heptatrien-6-ynes
| Autor: | Peter M. Gannett, Zhongguo Wang, and Anna Tarli, Kung K. Wang |
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| Rok vydání: | 1996 |
| Předmět: | |
| Zdroj: | Journal of the American Chemical Society. 118:10783-10791 |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | On heating in refluxing benzene, acyclic enyne−allene 4 underwent intramolecular transformations in a sequence with an initial Myers cycloaromatization to form α,3-didehydrotoluene biradical 5 followed by a 5-exo cyclization of the benzenoid radical center in 5 to produce 6. Biradical 6 then decayed through a 1,5-hydrogen shift to furnish o-quinodimethane 7, which in turn was captured in an intramolecular Diels−Alder reaction to afford 8 having the tetracyclic steroidal skeleton in a single step from 4 in 50% isolated yield. Similarly, acyclic enyne−allene 16 having one of the tethers shortened by one carbon atom furnished 18 having the fused 5,6,6,5-ring system. Tetracycle 19 substituted with an angular methyl group was obtained from 17. In the cases of 24 and 34, a predominant 1,5-hydrogen shift of an allylic hydrogen to the benzenoid radical center of biradicals 26 and 35 followed by a homolytic coupling produced spiro derivatives 31 and 40, respectively. On the other hand, a preferential 7-endo ring c... |
| Databáze: | OpenAIRE |
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