Lithiation of N-(1-cyanoalkyl)imines with LDA generates new N-lithiated azomethine ylide 1,3-dipoles which show enhanced reactivity toward dipolarophiles. They undergo exclusively regio- and stereoselective 3+2 cycloaddition reaction with α,β-unsaturated esters to give 1-pyrrolines after the elimination of LiCN. Metallic bases other than LDA can be also effective. Such high regio- and stereoselectivity is explained by the involvement of N-metalated azomethine ylides.
用
LDA对N-(1-
氰烷基)
亚胺进行
锂化,会生成新的N-
锂化的
亚胺烯基1,3-偶极体,这些偶极体对偶极体亲电试剂显示出增强的反应性。它们与α,β-不饱和
酯发生专一的区域选择性和立体选择性的3+2环加成反应,经过LiCN的消除后生成1-
吡咯啉。除了
LDA以外的
金属碱也可以有效。这种高区域选择性和立体选择性可以通过N-
金属化的
亚胺烯基的参与来解释。