Lewis acid N-heterocyclic carbenes (NHC) Research & information: general amines asymmetric aldol reaction asymmetric catalysis asymmetric synthesis cooperative catalysis electrochemistry enantioselectivity epoxide imines kinetic resolution methanol/water mixtures organic electrosynthesis organocatalysis photoredox catalysis proline radical additions radical-radical couplings ring-opening salen complexes stereoselectivity sustainability transition-metal catalysis umpolung umpolung chemistry visible light