1,3-Diol Fragmentation Using a Reactive Benzylic Hydroxyl Group as a Nucleofuge. Synthesis of a Tobacco Sesquiterpene

A benzylic hydroxyl group activated by electron-donative aromatic function was found to be a remarkably reactive nucleofuge for 1,3-diol fragmentation. Thus, treatment of α-(2,6-dimethoxy-4-methylphenyl)-2β-hydroxy-2α,5,5,8aβ-tetramethyl-4aα-decahydro-lβ-naphthalenemethanol with pyridinium chloride or pyridinium p-toluenesulfonate in dichloromethane underwent the 1,3-diol fragmentation smoothly to produce r-1-[(E)-2-(2,6-dimethoxy-4-methylphenyl)ethenyl]-t-2-(3-oxobutyl)-1,3,3-trimethylcyclohexane (24) in quantitative yield. Starting from 24, a tobacco sesquiterpene, 4-(2,2,6-trimethyl-6-vinylcyclohexyl)-2-butanone, was synthesized in racemic form by seven steps.