Pericyclic Cascade with Chirality Transfer: Reaction Pathway and Origin of Enantioselectivity of the Hetero-Claisen Approach to Oxindoles

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+2 cycloaddition step, which installs the stereochemistry, and a chirality transfer step facilitated by a hetero‐[3,3]‐sigmatropic rearrangement (see picture; PG=protecting group).