Synthesis of N-Arylimidazoles by Catalytic Cross-Cycloaddition of Isocyanides

Significance

A direct synthesis of N-arylimidazoles via Cu(I)-1,10-phenanthroline-catalyzed cross-cycloaddition between two different iso­cyanides is reported. This procedure allows the use of crude isocyanides formed from the starting stable formamides (step1), that is, N-aryl form­amides and ethyl N-formylglycine, without affecting the yields. Previously reported procedures require the use of strong base and high temperature, conditions which are incompatible with the unstable isocyanides. The present method proceeds under mild conditions. It was suggested that complexation of the Cu(I) ligand with the aryl ring of the isocyanide renders the isocyanide carbon more electrophilic to facilitate the reaction with the aliphatic isocyanide. A plausible mechanism which offers a rationalization why the reaction succeeds only with aromatic isocyanides was proposed.