Synthesis of α-aminophosphonic and α-aminophosphinic acids and derived dipeptides from 4-acetoxyazetidin-2-ones

4-Oxoazetidin-2-ylphosphonates and 4-oxoazetidin-2-ylphosphinates, obtained from the Arbusov reactions of 4-acetoxyazetidin-2-one and 4a-acetoxy- 3ß-phthalimidoazetidin-2-one with a variety of phosphites and phosphonites, were hydrolysed to ß-phosphono- and ß-phosphino-ß-alanine derivatives which were converted into alanyl dipeptides, conditions for the sequential removal of protecting groups for carboxylic acids, phosphonic acids, and amines were investigated.