Phosphine-mediated [2 + 1] cyclization of coumarins for the efficient construction of cyclopropa[c]coumarin scaffolds

Abstract

A phosphine-mediated [2 + 1] annulation of coumarins with α-keto esters or isatins was reported, leveraging in situ-generated Kukhtin–Ramirez adducts as key intermediates to efficiently access both cyclopropa[c]coumarin cores and spirooxindole-fused cyclopropa[c]coumarin architectures. The reaction proceeds under mild conditions, tolerates a broad substrate scope, can be scaled to gram quantity and thus exhibits pronounced practical potential.