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Title
| - Rearrangement of Annelated Housanes to Triquinane-LikeHydrocarbons by Electron Transfer (1,3-Cyclopentanediyl RadicalCations) and Acid Catalysis (Cyclopentyl Carbenium Ions)
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Abstract
| - The electron-transfer-catalyzed rearrangement of the annelated housane 4a on treatment withtris(p-bromophenyl)aminium hexachloroantimonate (TBA•+SbCl6-) affords regioselectively the twoisomeric olefins endo-5a and 6a by 1,2 migration of the two groups at the methano bridge. Acid-catalyzed rearrangement gives in addition to endo5a and 6a also the regioisomer endo-7a as majorproduct. The formation of both rearrangement products endo-5a and 6a suggests a planarconformation for the radical-cation and carbocation intermediates. The regioselectivity is rationalizedin terms of electronic stabilization of the radical versus cationic sites by the substituent at therearrangement termini in the radical-cation and carbocation intermediates. Of interest forpreparative purposes, the annelated housane 4a leads under electron-transfer conditions to unusualtriquinane-related olefins by means of an unprecedented synthetic pathway.
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