MN(III)-BASED OXIDATIVE FRAGMENTATION CYCLIZATION REACTIONS OF UNSATURATED CYCLOBUTANOLS

Allylic cyclobutanols 1, 10, 21, 27, 32, 39, 51, and 58 are oxidativel y fragmented by Mn(OAc)3.2H2O in EtOH to give tertiary radicals as sho wn in eq 1. These tertiary radicals undergo both 6-endocyclization to the alpha,beta--unsaturated ketone to afford a-keto radicals and 5-exo -cyclization to provide beta-keto cyclopentylmethyl radicals. The a-ke to radicals produced by 6-endo-cyclization are reduced to ketones or d imerize. The beta-keto radicals formed by 5-exo-cyclization are oxidiz ed by Cu(OAc)2 to yield methylenecyclopentanones and rearrange to give 3-oxocyclohexyl radicals that are oxidized by Cu(OAC)2 to afford cycl ohexenones. Acetylenic cyclobutanols 47, 49, and 65 are oxidatively fr agmented by Mn(OAC)3.2H2O in EtOH to provide tertiary radicals that cy clize to give alpha-keto vinyl radicals, which abstract a hydrogen ato m to yield methylenecyclopentanones. Pentenylcyclobutanol 75 is oxidat ively fragmented by Mn(OAc)3.2H2O to afford tertiary radical 74, which cyclizes to furnish cyclopentylmethyl radicals 77 and 78, which are o xidized by Cu(OAC)2 to methylenecyclopentanes 76 and 79.