2-Naphthol oxidative cross-coupling

With the bisoxazoline hgand (S)-Phbox and CuCl, the asymmetric oxidative couphng of 2-naphthol and hydroxy-2-naphthoates resulted in an asymmetrically substituted 2,2 -binaphthol with ee s of up to 65% [260]. On the basis of the previous results obtained with this catalyst system, the asymmetric oxidative cross-coupling polymerization of 2,3-dihydroxynaphthalene [261] and methyl 6,6 -dihydroxy-2,2 -binaphthalene-7,7 -dicarboxylate [262] as well as the copolymerization of 6,6 -dihydroxy-2,2 -binaphthalene and dihexyl 6,6 -dihydroxy-2,2 -binaphthalene-7,7 -dicarboxylate with Cu diamine catalysts were carried out imder aerobic conditions, using O2 as the oxidant, and a cross-coupling selectivity of 99% was achieved [263]. 

CATALYTIC OXIDATIVE CROSS-COUPLING REACTION OF 2-NAPHTHOL DERIVATIVES... 

SCHEME 143. Oxidative cross-coupling of 2-naphthol and 2-(p-hydroxyphenyl)ethanol... 

Hovorka M, Gtinrerova J, Zavada J (1990) Highly selective oxidative cross-coupling of substituted 2-naphthols a convenient approach to unsymmetrical 1, 1 -binaphthalene-2, 2 -diols. Tetrahedron Lett 31 413—416... 

Vyskocil S, Smrcina M, Lorenc M, Hanus V, Polasek M, Kocovsky P (1998) On the Novel two-phase oxidative cross-coupling of the two-component molecular crystal of 2-naphthol and 2-naphthylamine . Chem Commun 585-586... 

Oxidative cross-coupling of 2-naphthols is catalyzed by Cu(OH)Cl-TMEDA and assisted by Yb(OTf)3. Under such conditions BINOL containing a single methyl ester at C-3 is formed with >99% selectivity. ... 

Oxidative cross-coupling of two electronically-different 2-naphthols with CuCl2 in the presence of tert-butylamine Preparation of 3-methoxy carbonyl-1,1 -binaphthyl-2,2 -diol (395) [58]... 

Scheme 7.22 Cu-Catalyzed asymmetric oxidative cross-coupling of 2-naphthols. DCE = 1,2-dichloroethane.

Table 8.2 shows the results of the cross-coupling reaction between two differently substituted 2-naphthol derivatives using the CuCl-(5)Phbox catalyst. In conclusion, the first catalytic asymmetric oxidative coupling with a high cross-coupling selectivity was accomplished under mild conditions. 

They next studied the asymmetric oxidative polymerization of achiral 2,3-dihydroxynaphthalene (Scheme 42). The polymerization of this monomer with CuCl2-(-)-sparteine complex resulted in a low yield and gave a low molecular weight oligomer, whereas the polymerization with CuCl-(S)-Phbox quantitatively gave a polymer with Mn of 10 600-15 300. The enantioselectiv-ity attained in this polymerization, however, was estimated to be low, with 43% ee from the model reaction [169]. When vanadyl sulfate (VOSO -Phbox complex was used instead of the copper catalyst system, the enantioselectivity was improved up to 80% ee [170]. Asymmetric cross-coupling polymerization of two kinds of naphthol derivatives was also reported [171,172]. 

Other Reagents for the Oxidative Coupling Reaction Tab. 23. Copper(ll)/amine-mediated cross-coupling of variously substituted 2-naphthol derivatives. 

It should be noted that in most cases it is Cu-eatalyzed asymmetric oxidative biaryl homo-coupling reactions that are deseribed. On the contrary, successful examples of asymmetric oxidative biaryl eross-coupling reactions are rare. Habaue and co-workers discussed a highly eross-selective oxidative biaryl coupling between 3-hydroxy-2-naphthoates and 2-naphthols without ester functionality by a chiral Cu-BOX catalyst.The reactions proceed in a highly cross-eoupling selective manner with moderate enantioselectivity (up to 70% ee) (Scheme 3.7). Later, it was found that Lewis acids such as... 

Copper(II) amine complexes are very effective catalysts for the oxidative coupling of 2-naphthols to give symmetrical l,F-binaphthalene-2,2 -diols. Recent work has extended this methodology to the cross-coupling of various substituted 2-naphthols. For example, 2-naphthol and 3-methoxycarbonyl-2-naphthol are coupled under strictly anaerobic conditions using CuCU/tert-butylamine in methanol to give the unsymmetrical bi-naphthol in 86% yield (eq 20). 

In biatyl synthesis, although transition metal catalyzed aryl-aryl crosscoupling reactions have been widely exemplified using Suzuki-type reactions, CDC reactions between sp C-H bonds leading to sp C-C bonds are scarce. In 2010, Katsuki reported an enantioselective CDC reaction between two naphthol moieties catalyzed by a chiral iron(salan) complex under aerobic oxidative conditions (Scheme 4.23). Using 4 mol% of the iron(salan) complex 23-A as the catalyst in toluene at 60 °C for 48 h, two different 2-naphthols were coupled and the cross-coupled derivatives were isolated with moderate yields (44-70%) and good ee (87-95%). It must be pointed out that the homocoupling derivatives are also obtained in low yields. 

Cross-coupling between two phenols (or naphthols) is useful for producing bisphenol (or binaphthol) products. Oxidative homodimerization of 2-naphthol has been well documented in the literature. However, it is difficult to achieve cross-coupling between two different phenols, and their oxidation potentials must be sufficiently different in order to oxidize one phenol selectively. 

Kozlowski and co-workers found that asymmetric cross-coupling between electronically tuned 3-acyl-substituted 2-naphthols was catalyzed by a chiral Cu-diamine complex (Scheme 7.22). The Cu catalyst acts as an oxidation catalyst for naphthol coupling, and the resulting reduced Cu complex is reoxidized by O2 as the sole oxidant. 

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