Aminophosphonic derivatives of chromone.: Synthesis of novel chromone-3-(α-amino) methanephosphonic acids

Reactions of 3-formylchromones with benzyl carbamate and triphenyl phosphite in acetic acid lead to the corresponding diphenyl chromone-3-[alpha(-N-benzyloxycarbonyl)amino]methanephosphonates 2 in high yields. Deprotection of the Z-substituted diphenyl esters 2 by means of acetic hydrogen bromide solution and the subsequent hydrolysis by means of 20% aq. HCl, lead to the final chromone-3-(alpha -amino)methanephosphonic acids 4. Attempts of synthesis of the corresponding chromone-2- aminophosphonic derivatives by this way, have failed. On the other hand, chromone-2-(alpha -amino)methanephosphonic acid (6) was successfully obtained by an addition of tris(trimethylsilyl) phosphite to the aldimine, which was formed from the 2-formylchromone.