Highly enantioselective sulfa-Michael addition reactions using N-heterocyclic carbene as a non-covalent organocatalyst† †Electronic supplementary information (ESI) available. CCDC 1047559. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc00878f

We report the first asymmetric sulfa-Michael addition (SMA) reactions using a chiralN-heterocyclic carbene (NHC) as a non-covalent organocatalyst. We demonstrate that a triazolium salt derived NHC functions as an excellent Brønsted base to promote enantioselective carbon–sulfur bond formation. The reaction is applicable to a wide range of thiols and electrophilic olefins. Notably, quaternary chiral centers bearing both an S atom and a CF3 group were synthesized with excellent asymmetric control. Mechanistic studies suggest that the facial discrimination is likely to be guided by non-covalent interactions: hydrogen bonding and p–p stacking.