An efficient resolution of phosphinous acid-boranes

A general protocol has been developed for the resolution of racemic P-stereogenic phosphinous acid-boranes. It employs cinchonine as the resolving agent and most frequently gives an access to the pertinent diastereomerically pure cinchoninium salt of the acid in a single crystallization step. The resolved acids were assigned their absolute configurations by chemical correlations with already known enantiomerically pure phosphinite-boranes.

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(R)-(−)-o-Anisylphenylphosphinous acid-boraneC13H16BO2P[α]D = −19.2 (c 1.04, CHCl3) (96% ee)Source of chirality: resolution of racemic acidAbsolute configuration: (R)

(+)-Benzylphenylphosphinous acid-boraneC13H16BOP[α]D = +57.9 (c 1.06, CHCl3) (100% ee)Source of chirality: resolution of racemic acid

(+)-(2-Naphthylmethyl)phenylphosphinous acid-boraneC17H18BOP[α]D = +57.8 (c 1.04, CHCl3) (100% ee)Source of chirality: resolution of racemic acid

(R)-(−)-(1-Naphthyl)phenylphosphinous acid-boraneC16H16BOP[α]D = −40.8 (c 1.04, CHCl3) (100% ee)Source of chirality: resolution of racemic acidAbsolute configuration: (R)

(S)-(−)-Methylphenylphosphinous acid-boraneC7H12BOP[α]D = −21.7 (c 1.06, CHCl3) (100% ee)Source of chirality: resolution of racemic acidAbsolute configuration: (S)