N‐Heterocyclic Carbene Catalyzed [4+3] Annulation of Enals and <i>o</i>‐Quinone Methides: Highly Enantioselective Synthesis of Benzo‐ε‐Lactones

Abstract

Enantioselectivity through H bonding: An unprecedented [4+3] annulation of enals with o-quinone methides catalyzed by N-heterocyclic carbenes (NHCs) to give benzo-ε-lactones is described. High to excellent enantioselectivity was achieved by using a chiral triazolium NHC having a free OH group, which participates in a hydrogen-bonding interaction with the substrate.