Synthetic and mechanistic aspects of the reactions between bromodifluoromethyltriphenylphosphonium bromide and dibromofluoromethyltriphenylphosphonium bromide and trialkylphosphites
作者:Richard M. Flynn、Donald J. Burton、Denise M. Wiemers
DOI:10.1016/j.jfluchem.2008.04.003
日期:2008.7
exchange process involves the formation of difluorocarbene via dissociation of the intermediate difluoromethylene ylide, capture of the difluorocarbene by the trialkylphosphite to give [(RO)3P+CF2−], which captures bromine followed by dealkylation to the product, bromodifluoromethylphosphonate. The equilibria involved in the multi-step mechanism are all shifted to the phosphonate product by the final dealkylation
溴氟甲基三苯基溴化in以两种不同的方式与亚磷酸三烷基酯反应。溴代二氟甲基三苯基phosph与亚磷酸三烷基酯进行快速交换反应,以良好或极好的收率得到相应的溴代二氟甲基膦酸酯。用类似的二乙氧基苯基亚膦酸酯也发生类似的交换反应,得到相应的乙氧基苯基亚膦酸酯。从机理上讲,交换过程包括通过 中间体二氟亚甲基叶立德的离解形成二氟卡宾,亚磷酸三烷基酯捕获二氟卡宾以生成[(RO)3P + CF2-],它捕获溴,然后脱烷基化为产物溴二氟甲基膦酸酯。通过最后的脱烷基步骤,多步机理中涉及的平衡都转化为膦酸酯产物。相反,二溴氟甲基三苯基溴化does不与亚磷酸三烷基酯进行交换反应。亚磷酸酯用作卤化试剂,从二溴氟甲基phosph盐中提取溴,生成溴氟亚甲基叶立德,其很容易被醛或酮原位捕获,从而获得高收率的E / Z-溴代氟烯烃。没有观察到溴氟亚甲基叶立德的解离。