oxidative decarboxylation of cyclic alpha-amino acids having urethane-type N-protecting groups with lead tetraacetate [Pb(OAc)4] gave 2-hydroxy derivatives, which were transformed into the corresponding alpha-aminophosphonic acid esters by treatment of trialkyl phosphites in the presence of Lewis acids. Deprotection and ester cleavage of the products in the usual manner afforded cyclic alpha-aminophosphonic
1-aminophosphonic acids or reacted with Boc2O to yield N-Boc-protected 1-aminophosphonates. The enantiomers of 2-benzylthio-1-(t-butoxycarbonylamino)propylphosphonate were obtained from the racemate by chiral HPLC and converted to phosphonic acidanalogs of (R)- and (S)-homocysteine, (R)- and (S)-2-aminobutyric acid and (S)-methionine, all of ee >97% as determined by chiral HPLC.