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.
发现由供电子芳香族官能团激活的苄基羟基是 1,3
-二醇裂解的显着反应性离核基团。因此,用
氯化
吡啶鎓或
对甲苯磺酸吡啶鎓在
二氯甲烷中处理α-(2,6-二甲氧基-4-甲基苯基)-2β-羟基-2α,5,5,8aβ-四甲基-4aα-十氢-1β-
萘甲醇进行了处理1,3
-二醇顺利裂解生成r-1-[(E)-2-(2,6-二甲氧基-4-甲基苯基)
乙烯基]-t-2-(3-氧代丁基)-1,3,3定量产率的-三
甲基环己烷(24)。以24为起始原料,通过7步外消旋形式合成了烟草
倍半萜4-(2,2,6-三甲基-6-
乙烯基环己基)-2-
丁酮。