Synthesis of Chiral Bifunctional (Thio)Urea N-Heterocyclic Carbenes

The rapid and modular synthesis of the first bifunctional N-heterocyclic carbenes bearing a (thio)urea moiety as H-bond donor group was reported. Different analogues could be accessed in seven steps from cheap (S)-pyroglutamic acid in good overall yields (14-30%). The synthesized carbenes were active catalysts in the benzoin reaction.