Synthesis of 1,3-dihydro-2H-benzimidazol-2-one from 2-aminobenzamide

A method for the synthesis of 2-henzimidazolone ( 1 ) has been devised which does not depend on 1,2-diaminobenzene ( 2 ) as a starting material. This method produces 1 in good yield by the reaction of hypohalite with 2′-carbamoylphthalanilic acid ( 7 ), a compound readily prepared by the reaction of 2-aminobenzamide ( 3 ) and phthalic anhydride. Contrary to prior indications 1 can be hydrolyzed in the presence of acid at temperatures greater than 200 giving excellent yields of 2.