The α-bromo cycloalkyl aryl ketones 2a-d on heating with zinc chloride in methanol furnished in moderate to good yields the ring-contracted products 3a-d having gem methyl carbomethoxy function. The acetals of the related α-bromo ketones 7a-c, lacking the methyl group on the halogen-bearing carbon atom, afforded in acceptable yields the ring-contracted esters 8a-c when heated in protic solvent. The limitation of the present ring-contraction procedure has been discussed.
加热α-
溴环烷基芳基酮2a-d与
氯化锌在
甲醇中反应,获得了中等到良好的产率的环收缩产物3a-d,具有gem-甲基碳甲氧基功能。相关的α-
溴酮7a-c的醇醚,缺乏
氯原子邻近的甲基,经过加热在质子溶剂中反应,获得了可接受产率的环收缩酯8a-c。对目前的环收缩反应程序的局限性进行了讨论。