Unstable 2-cyclopropylidene-1,3-diones 3 can be trapped by isocyanides 8 to give [4 + 1]-cycloadducts 9 and 12. In the case of Meldrum's acid, as the dioxo component, spirotricyclic imides 15 are isolated due to an easy degradation of the primary cycloaddition products 14 in methanol. Subsequent reactions are described for the [4 + 1]cycloadducts leading to a cyclopropanecarboxamide 19b or to a phenylamino-substituted furan 20/21. Trapping of 3 by isocyanides 8 represents a novel second step in the concept of the twofold nucleophilic substitution at a cyclopropane.
不稳定的2-环丙叉-1,3-二酮3可以通过异
氰化物8捕获,生成[4+1]-环加成物9和12。在Meldrum酸作为二氧组件的情况下,由于初级环加成产物14在
甲醇中容易降解,因此分离出螺
三环咪唑15。后续反应描述了通过[4+1]环加成物形成
环丙烷羧酰胺19b或
苯胺取代的
呋喃20/21。通过异
氰化物8捕获3是
环丙烷双亲核取代概念中的一个新颖的第二步。