2-Amino-2-seleno-5,5-dimethyl-1,3,2-dioxaphosphorinane reacts with acyl chlorides (4-chlorobenzoyl chloride or pivaloyl chloride) yielding the respective N-acyl selenophosphoramides. These derivatives do not isomerise to the related selenocarbonyl imides. X-ray study of N-(4-chlorobenzoyl)-2-amino-2-seleno-5,5-dimethyl-1,3,2-dioxaphosphorinane indicates that the selenium atom is placed in the equatorial position. The next compound studied, N-pivaloyl-2-amino-2-seleno-5,5-dimethyl-1,3,2-dioxaphosphorinane, crystallises with both axial/equatorial conformers present in the asymmetric unit. Finally, 2-amino-2-seleno-5,5-dimethyl-1,3,2-dioxaphosphorinane is present in the solid state in the form with the selenium atom in the axial position. The results are presented together with X-ray structures of previously synthesised and described cyclic O-acyl monoselenophosphates.