Kinetic studies for cyclization of carbon-centered radicals to N-aziridinyl imino group

Abstract

The radical cyclization of N -aziridinyl imines has been known to provide a reliable method for generating 5- and 6-membered ring radicals from acyclic radical precursors. The kinetic studies for intramolecular addition of carbon-centered radicals to N-aziridinyl imino group were carried out. The kinetic data have been obtained by the relative ratio of the cyclized product and the direct reduction product in the presence of a large excess amount of tributyltin hydride. The cyclized products consisted of two products resulting from further cyclization of the intermediate radical via cyclopropyl rearrangement. The ratio of two products was analyzed by HPLC, from which the rate constant(k) was obtained. The value of rate constant$(k(C=N-Az)^6)$ was $7.3\times10^5s^{-1}$. This value was similar to the rate constant$(k(C=C)^5)$ value for the 5-exo radical cyclization of carcon-centered radical to a double bond. In addition, the rate constant $(k(C=N-Az)^5)$ value of 5-exo cyclization by carboncentered radical to N-aziridinyl imino group may be larger than $1\times10^8s^{-1}$, but the exact value was not obtained.