A simple direct phosgeneless route to N-heteroaryl unsymmetrical ureas

A new simple approach to the synthesis of unsymmetrical ureas HetNC(O)NRR¢ (HetNH = pyrrole, indole, carbazole; R, R¢ = H, alkyl, aryl) has been explored, which involves the direct reaction of the N-phenoxycarbonyl derivatives of pyrrole, indole and carbazole, HetNCO2Ph, with amines. The aminolysis reaction can be catalyzed by the amidine base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) under usually very mild conditions and provides a straightforward convenient entry into the target products through a route which avoids the traditional protocols based on multistep procedures and toxic phosgene or phosgene-derivatives