Resolution and Stereochemistry of <i>tert</i>-Butylphenylphosphinous Acid−Borane

A combined use of ephedrine and cinchonine as resolving agents enabled facile resolution of racemic tert-butylphenylphosphinous acid−borane (1) into the two enantiomers in ca. 31−32% yield each. The resolved 1 served as a model substrate to study stereoselective synthetic transformations of phosphinous acid−boranes yielding optically active phosphinite−borane, boranatophosphinous−sulfonic anhydride, secondary phosphine−borane, tertiary phosphine−borane, secondary phosphine oxide, and phosphinic halides. By the judicious choice of the reaction paths, either enantiomer of tert-butylphenylphosphine−borane and of tert-butylmethylphenylphosphine−borane could be stereoselectively obtained from a single enantiomer of 1.