Development of Highly Selective Reactions Based on Novel Ring Transformations

通过将二溴卡宾加成到烯烃或硅烯醇醚中得到的GEM-二溴环丙烷的新型转化反应，发展了高选择性的反应。硅胺在Ni-lt；(CO)_4&gt；诱导的GEM-二溴环丙烷的羰基化反应中的成功应用有助于环丙烷的一步立体选择性GEM功能化。这种转变被认为是通过中间体镍烯醇酸盐对亲电体的攻击而实现的。邻位含氯或氯甲基(或甲氧基甲基)取代基的GEM-二溴环丙烷与醇或胺发生Ni&lt；(CO)_4&gt；诱导的开环酮基化反应，分别得到不饱和羧酸衍生物。使用硅胺导致与相应的羧酸衍生物的烯醇酸盐与亲电试剂缩合。通过GEM-二溴硅氧基环丙烷的自发开环反应，将二溴卡宾加成到硅酮缩醛中，得到了不饱和的羰基化合物。通过用二烷基膦酸盐和三乙胺处理从而获得的α-溴-α-溴-α-不饱和酯或内酯进行还原去共轭，以立体选择性地产生相应的-lt；β&>t；-不饱和化合物。这两种方法都被有效地应用于天然化合物果核蛋白的合成。

Highly selective reactions have been developed by novel transformations of gem-dibromocyclopropanes which are prepared by the addition of dibromocarbene to olefins or silyl enol ethers. A successful utilization of silylamines in the Ni <(CO)_4> -induced carbonylation reactions of gem-dibromocyclopropanes contributes one-step stereoselective gem-functionalization of cyclopropanes. This transformation is considered to be achieved by the attack of intermediary nickel enolates on electrophiles. gem-Dibromocyclopropanes bearing the chloro or chloromethyl (or mesyloxymethyl) substituent at the vicinal position underwent the Ni <(CO)_4> -induced ring-opening carbonylation reactions with alcohols or amines leading to the <beta> , <gamma> - or <gamma> , <delta> -unsaturated carboxylic acid derivatives, respectively. Use of a silylamine resulted in condensation with an electrophile with the enolates of the corresponding carboxylic acid derivatives. The addition of dibromocarbene to silyl ketene acetals gave <alpha> -bromo- <alpha> , <beta> -unsaturated carbonyl compounds via spontaneous ring-opening of gem-dibromosiloxycyclopropanes. Reductive deconjugation of thus obtained <alpha> -bromo- <alpha> , <beta> -unsaturated esters or lactones was performed by treatment with dialkyl phosphonate and triethylamine to yield the corresponding <beta> , <gamma> -unsaturated compounds stereoselectively. Both methods were efficiently applied to the synthesis of the naturally occurring compound, pyrenophorin.