Reduction of Tertiary Phosphine Oxides by BH3 Assisted by Neighboring Activating Groups

Abstract

Tertiary sulfanylphosphine and aminoalkylphosphine oxides can be easily converted into the corresponding tertiary sulfanylphosphine- and aminoalkylphosphine-boranes, respectively, through the facile P=O bond reduction by borane complexes. The easy reduction of the strong P=O bond by BH3, a mild reducing agent, has been achieved through an intramolecular P=O -- B complexation directed by proximal SH or NH activating groups located at the α- or β-position to the P=O bond. A generalized reduction mechanism has been proposed.