New frontiers of N-heterocyclic carbene catalysis

N-heterocyclic carbene （NHC） is both a family of strong o-donor ligands for transition metals and a privileged class of organocatalysts with synthetic potential that rivals popu- lar amine and phosphoric acid catalysts. NHC was found as a key catalytic species in thiamine diphosphate catalyzed biochemical reactions [1]. However, due to their inherent chemical instability, free NHCs had not been isolated until 1991 by Ardungo et al. [2]. Since then, the use of chiral NHC as a versatile organocatalyst has enjoyed tremendous advances and has helped to transform modem synthetic chemistry. There are over 2000 research papers dealing with both ＂N-heterocyclic carbene＂ and ＂Catalysis＂ in the past 15 years [3].