Primary alkylamines, beta-aryloxyethylamines, or N-[beta-(2-methoxyphenoxy)ethyl]-alpha,omega-diaminoalkanes react with alkyl divinylphosphinates or phenyl(divinyl)phosphine oxide to give the corresponding 4-alkoxy(4-phenyl)-1-alkyl-4-oxo-1,4-azaphosphorinanes. Reactions of the latter with mono- or dihaloalkanes afford 4-phosphapiperidinium halides. 1,4-Azaphosphorinanes containing a beta-aryloxyethyl fragment exhibit hypotensive activity.