Synthesis of pyrazoline-derived N-vinyl nitrones through an unexpected selective [3 + 2] cycloaddition

Abstract

A variety of pyrazoline-derived N-vinyl nitrones was prepared in moderate to good yields with high diastereoselectivity through the base-promoted regioselective [3 + 2] cycloaddition of N-vinyl chalcone nitrones and hydrazonoyl chlorides under mild reaction conditions. Mechanistic studies revealed that the E isomers of N-vinyl nitrones facilitated conversion into pyrazoline-derived N-vinyl nitrones better than the Z isomers. The present method features a broad substrate scope, good functional group tolerance, and high regioselectivity and diastereoselectivity, while a novel type of N-vinyl nitrones was formed, and N-vinyl nitrones served as dipolarophiles.