BINOL: A Versatile Chiral Reagent

Abstract

The aim of enantioselective synthesis or catalysis is to produce chiral products starting from achiral substrates by exploiting the presence of chiral reagents. The enantiomeric atropisomers of 1,1′-binaphthyl-2,2′-diol (BINOL) are the best-known representatives of axially chiral molecules and were first prepared as racemate in 1873 by von Richter. [1] BINOL is used for both stoichiometric and ­catalytic asymmetric reactions. [2] The chiral atropisomers (R)-1 ([α]20 D +35.5 THF, c 1), mp 205-211 °C and (S)-1 ([α]20 D -34.5, THF, c 1), mp 205-211 °C are stable at high temperature and allow numerous asymmetric reactions under various experimental conditions (Figure 1). [3] BINOL-mediated asymmetric oxidation, reduction and C-C bond-forming reactions are well-established reactions in ­organic synthesis. BINOL (1) can be easily prepared from 2-naphthol using Cu-amine complexes to give racemic BINOL which can be converted into (R)-BINOL [(R)-1] or (S)-BINOL [(S)-1] by enzymatic resolution [4] or via chemical resolution (Scheme 1). [5]