(R)-1,1′-Bi-2,2′-naphthol

[18531-94-7] C20H14O2 (MW 286.33) (chiral ligand and auxiliary1) Alternate Name: BINOL. Physical Data: mp 208–210 °C; [α]21 +34° (c = 1, THF). Solubility: sol toluene, CH2Cl2, EtNO2. Form Supplied in: white solid; widely available. Preparative Methods: racemic 1,1′-bi-2,2′-naphthol (BINOL) is most conveniently prepared by the oxidative coupling reaction of 2-naphthol in the presence of transition metal complexes (eq 1).2 The resolution of racemic BINOL with cinchonine may be performed via the cyclic phosphate (eq 2).3 An alternative procedure to provide directly optically active BINOL is the oxidative coupling of 2-naphthol catalyzed by CuII salt in the presence of chiral amines (eq 3).4 The best procedure uses (+)-amphetamine as the chiral ligand and provides BINOL in 98% yield and 96% ee. Above 25 °C the CuII/(+)-amphetamine/(S)-BINOL complex precipitates while the more soluble CuII/(+)-amphetamine/(R)-BINOL complex is slowly transformed into the former complex. 9,9′-Biphenanthrene-10,10′-diol has also been prepared in 86% yield and with 98% ee by a similar asymmetric oxidative coupling of 9-phenanthrol in the presence of (R)-1,2-diphenylethylamine.5 (1) (2) (3) Handling, Storage, and Precautions: keep tightly closed, store in a cool dark place; on heating in butanol at 118 °C for 24 h, BINOL lost ∼1% of its optical rotation; at 100 °C for 24 h in dioxane–1.2 N HCl, BINOL lost 56% of its rotation; after 24 h at 118 °C in butanol–0.7 N KOH, BINOL lost 20% of its rotation.