The reaction of 1-phenyldimethylsilylmethyl-2-vinyl cyclopropane with acetals under the influence of TMSOTf proceeds smoothly to provide skipped dienes with exclusive E-olefin geometry regardless of the initial cis/trans configuration of the starting cyclopropane. The reaction is under stereoelectronic control where the intermediate Prins cation formed is stabilised by the adjacent cyclopropane grouping in a bisected conformation before undergoing silyl-directed collapse.
无论起始
环丙烷的初始顺式/反式构型如何,1-苯基二甲基甲
硅烷基甲基-2-
乙烯基环丙烷与
缩醛的反应在TMSOTf的影响下顺利进行,提供具有排他性E-烯烃几何结构的跳段二烯。该反应是在立体电子控制下进行的,其中形成的中间 Prins 阳离子在经历甲
硅烷基定向塌陷之前通过二等分构象中的相邻
环丙烷基团进行稳定。