Bisallylation of Zirconacyclopentenes and Ring-Closing Metathesis: A Route to Eight-Membered-Ring Compounds

The cyclization of various enynes with the Negishi reagent provides the corresponding bicyclic zirconacyclopentenes, which after exposure to allyl chloride in the presence of a catalytic amount of copper(I) chloride, undergo bisallylation to furnish 1,9-decadienes in good yields (42–89%). The dienes are subjected to ring-closing metathesis to afford bicyclic compounds with [6.3.0]bicycloundecane (8,5-fused ring system) or [6.4.0]bicyclododecane (8,6-fused ring system) frameworks in good to excellent yields (52–92%). Selective monoallylation of a selected zirconacyclopentene followed by carboxyethylation with ethyl chloroformate gives rise to the corresponding ester, which after metalation and reaction with allyl bromide, furnishes a 1,9-decadiene. Ring-closing metathesis then yields the expected eight-membered cyclic product in 92% yield. This procedure constitutes a new pathway to bicyclic carbocyclic systems starting from 1,ω-enynes.各类炔烯（enynes）与根岸试剂（Negishi reagent）发生环化反应，生成相应的双环锆杂环戊烯（bicyclic zirconacyclopentenes）；该中间体在催化量氯化亚铜（copper(I) chloride）存在下与烯丙基氯（allyl chloride）作用，经双烯丙基化反应得到1,9-癸二烯（1,9-decadienes），产率优良（42%~89%）。将所得二烯烃进行闭环复分解（ring-closing metathesis）反应，可得到具有[6.3.0]双环十一烷（[6.3.0]bicycloundecane，8,5稠合环系）或[6.4.0]双环十二烷（[6.4.0]bicyclododecane，8,6稠合环系）骨架的双环化合物，产率良好至优异（52%~92%）。对选定的锆杂环戊烯进行选择性单烯丙基化，再通过氯甲酸乙酯（ethyl chloroformate）进行羧乙基化反应，得到相应的酯中间体；该中间体经金属化（metalation）后与烯丙基溴（allyl bromide）反应，生成1,9-癸二烯。随后对该产物进行闭环复分解反应，以92%的产率得到目标八元环产物（eight-membered cyclic product）。该方法为以1,ω-炔烯（1,ω-enynes）为起始原料构建双环碳环体系（bicyclic carbocyclic systems）提供了一条全新路径。