Synthesis of Phosphaguanidines by Hydrophosphination of Carbodiimides with Phosphine Boranes

The direct addition of anionic secondary
phosphine boranes to carbodiimides
yields both chiral and achiral phosphaguanidine boranes under ambient
temperature conditions. An analogous preparation of menthol-derived
phosphinite boranes is also described. These products can be deborinated
to give the corresponding phosphines, and subsequently oxidized to
give phosphine oxides. The robustness of this method was further demonstrated
in the synthesis of structurally novel cyclic phosphaguanidines.