Oxidative 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...

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. 

Chiral Self-Dimerization of Vanadium Schiff-Base Complexes on Si02 and Their Catalytic Performances lor Asymmetric Oxidative Coupling of 2-Naphthol... 

BINOL and its derivatives have been utilized as versatile chiral sources for asymmetric catalysis, and efficient catalysts for their syntheses are, ultimately, required in many chemical fields [39-42]. The oxidative coupling of 2-naphthols is a direct synthesis of BINOL derivatives [43, 44], and some transition metals such as copper [45, 46], iron [46, 47] and manganese [48] are known as active metals for the reaction. However, few studies on homogeneous metal complexes have been reported for the asymmetric coupling of 2-naphthols [49-56]. The chiral self-dimerized V dimers on Si02 is the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol. 

Numerous cationic azo dyes are prepared by the action of /V-hydroxymcthyl-chloroacetamide on azo dyes in sulfuric acid medium, followed by displacement of the reactive chloro substituent by pyridine or trialkylamine. Of special significance for dyeing paper are dyes that are prepared by coupling of diazotized 2-(4 -aminophenyl)-5-methylbenzothiazole to acetoacetaiylides, pyrazolones, naphthols [143], or barbituric acid derivatives [144], followed by reaction with N-hydroxymethylchloro-acetamide and pyridine. The azo dye obtained by oxidative dimerization of 2-(4 -aminophenyl)-5-methylbenzothiazole may also be subjected to this conversion [145], Dye 51 colors paper yellow. 

Tab. 25. Copper(ll)-catalyzed oxidative dimerizations of substituted 2-naphthol derivatives.

Oxidations. Clean products are generally obtained by using alumina-supported reagents. For the oxidative dimerization of thiols by OMSO or NalOj, the conversion of hydroquinones to quinones and 2-naphthols to BINOLs in the presence of CuSO, the formation of lactones from a,co-diols under the influence of NaBrOj, and the hydrolytic defluorination of certain perfluoroalkylarenes, alumina has unique or positive effects. 

The coupling reaction involves oxidation of 2-naphthol by electron transfer to give an aryloxy radical, which then dimerizes to yield the product. The mechanism is shown here ... 

Naphthol can successfully be dimerized oxidatively, selectively through the o-site to give (22) using copper(II)-amine complexes (70%) or manganese(III) acetylacetonate (69%), and o-o coupling is the major paAway (90%) on ferricyanide oxidation of the trisubstituted phenol (23) to the orthodiphenoqui-none (24). In this context it is of interest that a compound obtained (74%) on ferricyanide oxidation of... 

Asymmetric oxidative dimerisation of S(+)-3,4,8-trimethyl-5,6.7,8-tetrahydro-2-naphthol in ether with potassium ferricyanide in aqueous 0.2M sodium hydroxide was effected by stirring at ambient temperature for 2 hours to afford the S,S-(+)-trans dimer in 62% yield (ref. 14). 

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