Design, Synthesis, and Organocatalytic Activity of N-Heterocyclic Carbenes Functionalized with Hydrogen-Bond Donors in Enantioselective Reactions of Homoenolates

A focused library of chiral imidazolinium salts functionalized with urea-type hydrogen-bond donor moieties has been prepared from the chiral pool. The corresponding N-heterocyclic carbenes were evaluated as organocatalysts in three enantioselective reactions involving homoenolate intermediates generated from enals. The catalysts proved competent in enantioselective cyclopentannulation and -lactonization reactions, a premiere for imidazoline-based NHCs. This work conveys some new ideas and knowledge on the concepts of bifunctional enantioselective organocatalysis applied to NHCs.