1-aminophosphonic acids and esters bearing heterocyclic moiety .2. Pyridine, pyrrole and imidazole derivatives

The benzylic amines (benzylamine, benzhydrylamine and benzyl carbamate) were applied in the synthesis of aminophosphonates derived from pyridine, pyrrole and imidazole. The Schiff bases obtained from corresponding heterocyclic aldehydes and benzylic amines were caused to react with diphenyl phosphonate or dibenzyl phosphonate to form corresponding heterocyclic aminophosphonates in good yields. The N-(benzylamino)-phosphonates were deblocked by catalytic hydrogenolysis. The benzhydryl group from the phosphonates was removed by acidic hydrolysis, and the carbobenzyloxy group from the phosphonates can be easy removed by treatment with a solution of 30% HBr in acetic acid, as well. It was found that during acidic hydrolysis of 2- and 4-pyridylmethylaminophosphonates a rearrangement occurred, combined with a cleavage of C-P bond in the phosphonate molecules and subsequent formation of the corresponding amines.