The position of conformational equilibrium of 1,3,5-diazaphosphorinanes was shown in [1 ] to be controlled by interaction of the heteroatoms in the P--C--N and N---C--N systems. However, these interactions do not affect the reactivity of the compounds [2, 3]. The interaction of heteroatoms in the P---C-O--B system is significant according to a study of the conformation of 1,3,2,5-dioxaboraphosphorinanes [4] and their reactivity with electrophiles and nucleophiles [5, 6]. This interaction is manifested in the reduced nucleophilicity of the P atom [5] and the high lability of the P--C bond [7]. It seemed interesting to study the reactivity of 1,3,2,5-dioxaboraphosphorinanes relative to borane and to compare the stability of the complexes obtained to that of aminoalkylphosphines with borane. The 1,3,2,5-dioxaboraphosphorinanes were reacted with borane in THF at room temperature using excess borane prepared by reduction of BFs.Et20 with LiAIH 4.