Dimerization of 2-naphthol

Scheme 16. Large-scale iron(lll)-mediated oxidative dimerization of 2-naphthol (68a).

Tab. 15. Survey of iron(lll) sources used in the two-phase oxidative dimerization of 2-naphthol (6 a).

Tab. 17. Microwave-assisted oxidative dimerization of 2-naphthol derivatives by iron(lll).

Tab. 34. Sparteine-mediated electrocatalytic asymmetric oxidative dimerization of 2-naphthol and...

Tab. 38. Enantioselective dimerization of 2-naphthol (and 2-naphthylamine) derivatives promoted by vanadium complexes 219 and 220.

The most frequently applied ligands are 2,2 -binaphthol (BINOL la) and 2,2 -bis(diphenyl-phosphino)binaphthyl (BINAP lb). Both antipodes of these compounds are commercially available in enantiopure form, though not at little cost [3]. It is rewarding, therefore, to become acquainted with the syntheses of these compounds, which have been described in detail [4J and have been simplified substantially on the basis of recent publications [5J. The iron(lIl)-catalyzed dimerization of 2-naphthol (2) to give racemic BINOL (rac)-la succeeds smoothly and on a large scale (Scheme 1). Its resolution can be achieved easily with N-benzylcinchoidinium chloride (3) and yields both (/ )- and (5 )-la in high enantiomeric excesses. After conversion into the ditri-flate 4, enantiopure la can be coupled with diphe-nylphosphine (or, in lower yield, with cheaper chlorodiphenylphosphine) in a nickel-catalyzed... 

Manganese chelates, such as manganese(III) acetonylacetonate were also tried as oxidants in the coupling of phenols and phenol ethers [125]. In one of the first examples binaphthol was prepared by the oxidative dimerization of 2-naphthol [126]. Although with this reagent overoxidation can be mostly avoided, low conversions make this method inferior to others. 

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