Radical cyclization of N-aziridinyl imines

Abstract

A fundamentally new approach, using 2-phenyl-N-aziridinyl imines, for the formation of five- and six-membered ring radicals from acyclic precursors has been studied. The radical cyclization of N-aziridinyl imines using structurally different radical precursors proceeded smoothly, yielding cyclized products in high yields. The radical cyclization of iodo aziridinyl imine in the presence of electron deficient alkenes with n-Bu$_3$SnH proceeded, yielding electon deficient alkene substituted cyclic compounds. This demonstrated the formation of two carbon-carbon bonds in succession at the same carbon. The radical cyclization of diaziridinyl imines proceeded, yielding the cyclized product bearing a carbon-carbon double bond. This demonstrated the efficacy of the aziridinyl imino group as a radical precursor as well as a radical acceptor. The competition between a formyl group and an imino group as a radical acceptor was studied, and this result indicated the radical cyclization of an alkyl radical to formyl and N-aziridinyl imine was competitive as 16:62. Furthermore, the competition between a keto and an imino group showed preferential attack of a vinyl radical to the imino group. The competition between an alkenyl and an N-aziridinyl group showed the preference of the alkenyl group over the imino group as a radical acceptor. The competition between a formyl and an N-aziridinyl imino group as a radical precursor showed the preferential attack of Bu$_3$Sn radical to the formyl group over the imino group. The preference of a keto group over an imino group was also observed. The competition study with alkenyl N-aziridinyl imine indicated the preference of the alkenyl group over the imino group as a radical precursor.