Studies towards the N-acylative Kinetic Resolution of Nobin

2-Amino-2′-hydroxy-1,1′-binaphthyl [NOBIN (1); Fig. 1] was first prepared as a racemate by Kočovský in 1991 via oxidative coupling of 2-naphthol and 2-naphthylamine in MeOH using stoichiometric tert-butylamine/ copper(II) chloride1–3. Subsequently, a variant employing aqueous iron(III) chloride was reported4,5, and (±)-NOBIN has been prepared from (±)-BINOL (3; Fig. 1) by a Bucherer reaction6. Kočovský has also shown that partial optical resolution concomitant with oxidative coupling can be achieved by inclusion of a stoichiometric amount of various chiral amines in place of tert-butylamine during oxidative coupling. This allows for initial precipitation of a complex of NOBIN, the copper salt and the chiral amine in up to 46% ee and subsequent fractional crystallisation can yield product with high levels of optical purity7–11. Optical resolution of scalemic or (±)-NOBIN by classical crystallisation with camphor sulfonic acid12,13, by imine exchange of achiral imine derivatives with chiral amines14 and by inclusion complexation with N-benzyl cinchonidinium chloride15 are alternative methods to obtain enantiomerically highly enriched (R)or (S)-NOBIN. Alterna-