Abstract: N-Acylanilides having electron-donating substituents attached at a proper position react with phosphorus (III) bromides forming the new heterocyclic system-2, 4, 1- benzoxazaphosphinine. 1-Arylimino-2, 4, 1-benzoxazaphosphinines are hydrolyzed with cleavage of an oxazaphosphinine ring affording mixed amides of 2, 4- diaminophenylphosphonic acid in high yield. Key words: arylamides, phosphorus (III) ...