Efficient Preparation of (S)- and (R)-tert-Butylmethylphosphine–Borane: A Novel Entry to Important P-Stereogenic Ligands

A novel one-pot reductive methodology for the synthesis of optically pure tert-butylmethylphosphine–borane is reported. The preparation uses as the starting material tert-butylmethylphosphinous acid–borane, which is available in both enantiomeric forms from cis-1,2-aminoindanol and tert-butyldichlorophosphine. The process is based on the reduction of a mixed anhydride, the configurational stability of which has been studied in several solvents and temperatures. Tetrabutylammonium borohydride was the best reducing agent allowing for the development of a practical process. To demonstrate the utility of the new methodology, the product obtained in this manner was used in the preparation of Quinox-P*.