Organocatalyzed Reduction of Tertiary Phosphine Oxides

A novel selective catalytic reduction method of tertiary phosphine oxides to the corresponding phosphines has been developed. Notably, the reaction proceeds smoothly with low catalyst loadings of 1–5 mol% even at low temperature (70 °C). Under the optimized conditions various phosphine oxides could be selectively reduced and the desired phosphines were usually obtained in excellent yields above 90%. Furthermore, we have developed a one-pot reaction sequence for the preparation of valuable phosphine⋅borane adducts. Simple addition of BH3⋅THF subsequent to the reduction step gave the desired adducts in yields up to 99%.