Synthesis of methylene cyclopropane-fused chromenes and dihydroquinolines by sequential [4 + 2]- and [1 + 2]-annulation

Abstract

A base promoted sequential [4 + 2]- and [1 + 2]-annulation of 2-hydroxychalcones or 2-tosylaminochalcones with prop-2-ynylsulfonium salts has been developed to give the corresponding methylene cyclopropane fused dihydroquinolines or chromenes in moderate to good yields. This transformation has advantage of wide substrate scope and functional group tolerance as well as excellent regioselectivity. Prop-2-ynylsulfonium salts act as both C₂ and C₁ synthons in the tandem processes.