Synthesis of Electronically Diverse Tetraarylimidazolylidene Carbenes via Catalytic Aldimine Coupling

A new method for synthesizing symmetrical N-heterocyclic imidazolium salts is described. Catalytic coupling of aldimines with cyanide followed by oxidation gives α-diketimines, which can then be cyclized with formaldehyde in acidic media. This two-step procedure requires no chromatography and allows the synthesis of electronically diverse 1,3,4,5-tetraarylimidazolylidene carbenes.