2-Ethoxy-6-oxo-1,2-azaphosphinane 2-oxide (3) has been prepared by cyclocondensation of ethyl 4-(P-amino-P-ethoxyphosphinoyl)butanoate (17). N-Alkylated derivatives of (3) were prepared by cyclocondensation of (17) in the presence of methyl iodide, allyl bromide and benzyl chloride. These derivatives reacted with organometallic reagents and bases to yield acyclic products.