Pericyclic cascade with chirality transfer: Reaction pathway and origin of enantioselectivity of the hetero-claisen approach to oxindoles

Abstract

A new pericyclic cascade is proposed for the chiral auxiliary-controlled synthesis of 3,3-disubstituted oxindoles from nitrones and ketenes. The remarkable acyclic 1,6-stereochemical induction, hitherto unexplained, is rationalized by a stereoselective 3+2cycloaddition step, which installs the stereochemistry, and a chirality transfer step facilitated by a hetero-[3,3]-sigmatropic rearrangement (see picture; PG=protecting group). © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.