Asymmetric synthesis of spiro[chroman-3,3′-pyrazol] scaffolds with an all-carbon quaternary stereocenter via a oxa-Michael–Michael cascade strategy with bifunctional amine-thiourea organocatalysts

Abstract

An efficient chiral bifunctional amine-thiourea catalysed cascade oxa-Michael–Michael addition of 4-alkenyl pyrazolin-3-ones to (E)-2-(2-nitrovinyl)phenol for the synthesis of chiral heterocyclic systems containing spiro[chroman-3,3′-pyrazol] scaffolds has been developed. This reaction afforded the desired products in high to excellent yields (up to 98%) with moderate to high enantioselectivities (up to 99%) and diastereoselectivities (up to 20 : 1) under low catalyst (15 mol%) concentration. This catalytic asymmetric reaction provides an efficient route toward the synthesis of chiral spiro[chroman-3,3′-pyrazol] derivatives containing three contiguous stereocenters which possess potential pharmaceutical activities.