Synthesis of symmetrical and unsymmetrical ureas using unsymmetrical diaryl carbonates

Appropriately substituted unsymmetrical diaryl carbonates react smoothly with primary amines to give the carbamates derived by nucleophilic displacement of the less electron rich aromatic substituent. Subsequent treatment of the carbamates with primary and secondary amines gives either symmetrical or unsymmetrical ureas in excellent yield and the overall process can be carried out as a ''one pot'' operation. Acetonitrile is the preferred solvent and addition of DBU facilitates the carbamate --> urea transformation.