Synthesis of C-heteryl-substituted aminomethylphosphonic acids derivatives

The available diethyl 5-hydrazino-2-p-tolyl-1,3-oxazol-1-ylphosphonate was readily acylated with chlorides of carboxylic acids of heterocyclic series. On heating in acetic acid it underwent the oxazole ring cleavage, recyclization and diethylation that was used to prepar the substituted 2-p-toluylaminomethylphosphonic acids containing a series of 2-heteryl-1,3,4-oxadiazol-5-yl residues in the α-position relative to the phosponyl group.