A Bifunctional N‑Heterocyclic Carbene as a Noncovalent Organocatalyst for Enantioselective Aza-Michael Addition Reactions

Chiral N-heterocyclic carbenes (NHCs) have been recently established as powerful catalysts for enantioselective bond-forming processes via noncovalent interactions. The underlying HOMO-raising activation of nucleophiles takes advantage of the strong Brønsted basicity of NHCs. However, the scope of compatible electrophiles has been quite limited. In this article, we report a bifunctional NHC with an embedded hydrogen-bonding motif that shows remarkable tolerance of various Michael acceptors in an asymmetric aza-conjugate addition reaction. The catalytic efficiency far exceeds that of the benchmark tertiary amine-thiourea scaffold.