Chemical conversion of cyclic alpha-amino acids to cyclic alpha-aminophosphonic acids

The 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 acids. The convenient chemical conversion of five- and six-membered cyclic alpha-amino acids to the corresponding cyclic alpha-aminophosphonic acids has been accomplished.