Manganese(III)-based oxidative fragmentation-cyclization reactions of unsaturated cyclobutanols
作者:Barry B. Snider、Nha Huu Vo、Bruce M. Foxman
DOI:10.1021/jo00077a054
日期:1993.12
Allylic cyclobutanols 1, 10, 21, 27, 32, 39, 51, and 58 are oxidatively fragmented by Mn(OAc)3.2H2O in EtOH to give tertiary radicals as shown 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-keto radicals produced by 6-endo-cyclization are reduced to ketones or dimerize. The beta-keto radicals formed by 5-exo-cyclization are oxidized by Cu(OAc)2 to yield methylenecyclopentanones and rearrange to give 3-oxocyclohexyl radicals that are oxidized by Cu(OAC)2 to afford cyclohexenones. Acetylenic cyclobutanols 47, 49, and 65 are oxidatively fragmented by Mn(OAC)3.2H2O in EtOH to provide tertiary radicals that cyclize to give alpha-keto vinyl radicals, which abstract a hydrogen atom to yield methylenecyclopentanones. Pentenylcyclobutanol 75 is oxidatively fragmented by Mn(OAc)3.2H2O to afford tertiary radical 74, which cyclizes to furnish cyclopentylmethyl radicals 77 and 78, which are oxidized by Cu(OAC)2 to methylenecyclopentanes 76 and 79.