An economic, practical access to enantiopure 1,1′-bi-2-naphthols: enantioselective complexation of threo-(1S,2S)-N-benzyl-N,N-dimethyl[1,3-dihydroxy-1-(4′-nitrophenyl)]-2-propylammonium chloride

An economic, convenient access to enantiopure (R)- and (S)-1,1′-bi-2-naphthol (BINOL) has been discovered. Racemic 1,1′-bi-2-naphthol was reacted with threo-(1S,2S)-N-benzyl-N,N-dimethyl-[1,3-dihydroxyl-1-(4′-nitrophenyl)]-2-propylammonium chloride (BDDNPAC) in water-containing acetonitrile under reflux until the solid dissolved completely, and then cooled to ambient temperature to isolate a yellow-greenish crystal consisting of BDDNPAC, (S)-BINOL, and water, which was analyzed by single crystal X-ray structural analysis. Enantiopure (S)- and (R)-1,1′-bi-2-naphthols were obtained in high yield after decomposition of the colored crystalline complex and evaporation of the acetonitrile solution removed from the complex crystals and successive crystallization. The chiral quaternary ammonium salt BDDNPAC can be recovered and reused without any decrease in efficiency.

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C16H24ClNO2[α]D20=+48.8 (c 1.184, EtOH)Source of chirality: synthesis from threo-(1S,2S)-2-amino-1-(4′-nitrophenyl)-1,3-propanediolAbsolute configuration: (1S,2S)

C38H39ClNO7[α]D20=-25.9 (c 1.012, DMF)Source of chirality: synthesis from BDDNPAC and racemic BINOLAbsolute configuration: (1S,2S,S)