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 degrees 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 center dot borane adducts. Simple addition of BH3 center dot THF subsequent to the reduction step gave the desired adducts in yields up to 99%.