Stereoselective synthesis of 5-substituted pyrrolo[1,2-c]imidazol-3-ones: access to annulated chiral imidazol(in)ium salts.

A two-step synthesis of N-heterocyclic carbene (NHC) precatalysts by diastereoselective or enantioselective lithiation of pyrrolo[1,2-c]imidazol-3-ones followed by POCl(3)-induced salt formation is described. The resulting 3-chloro-pyrroloimidazol(in)ium salts may be coordinated to palladium(II) upon NHC generation with t-BuLi at low temperature. The method may facilitate exploitation of these compounds as chiral organocatalysts or ligands in metal catalysis.