A study on the synthesis of the novel cyclic α-aminophosphonates and 2-alkoxy-2- oxo-1, 4, 2-oxazaphosphinanes 4a–r has been carried out. The title compounds were obtained in good yields by one-pot procedure using o-aminophenol, alkyl dichlorophosphinite, and ketones or benzaldehyde. One of their geometric stereoisomers was isolated and characterized. Configurations of 4k and one isomer of 4r have been established by X-ray diffraction analysis. The synthetic methods provide an easy access to the organophosphorus heterocycles with the ring system mentioned above. The abnormal chemical shifts of alkyl-substitute protons in 1H NMR spectra were given reasonable explanation.