Synthesis of P-Stereogenic Phosphines

Phosphines are commonly employed as ligands for late-transition-metal-catalyzed reactions. While a plethora of ligands with chirality α to the phosphine are used, the P-stereogenic counterparts are less common. This paper is a very nice report on the synthesis of these compounds, which are much more difficult to obtain. The use of (R)-i-Pr-PHOX as the ligand on the ruthenium center gave the best results. Sodium tert-amyloxide was the optimal base, while a variety of benzylic chlorides were shown to be appropriate electrophiles. The use of ethyl bromide gave lower yield and enantioselectivity (70% yield, 57% ee). The products were isolated as the air-stable borane adducts.