Bulky, Optically Active P-Stereogenic Phosphine–Boranes from Pure H-Menthylphosphinates

The transformation of readily available pure-H-menthylphosphinates into chiral phosphinous acid-boranes permits the elaboration of bulky P-stereogenic secondary phosphine–boranes. Taking advantage of the synthetic potential of these compounds, a broad range of hindered P-chiral tertiary phosphine–boranes has been prepared with excellent enantiomeric excesses. The utility of bulky o-tolylphosphines was illustrated by the synthesis of a rare enantiopure phosphapalladacycle (S P,S P)-12.