Oxidative coupling 2-naphthol

A catalytic version of the copper(II)-mediated stoichiometric chiral amine naphthol oxidative couplings has been developed as an extension of the successful achiral version. Smrcina and co-workers first carried out such a reaction in order to obtain information on the mechanism of their stoichiometric amine reactions. They obtained the biphenyl product (S)-207 in 41 % yield with a modest enantiomeric excess (32 % ee) (Scheme 56) [88]. 

In recent years, axially chiral binaphthalene derivatives have emerged as important ligands and chiraUty inducers in organic synthesis. Oxidative coupling of 2-naphthols represents a well estabhshed method for the preparation of binaphthols. The couplings are usually carried out by treating naphthols with more than an equimolar amount of a metal such as Fe(III), Mn(III),... 

The common denominator for all the previous approaches to the perylenequinones is a diastereoselective oxidative coupling of homochiral 2-naphthols. Our group proposed an alternative enantioselective convergent synthesis that would greatly... 

The stoichiometric oxidative coupling of various phenols proceeds with moderate selectivity (76% ee) in the presence of (-)-sparteine CuCl2, Eq. 106 (127). As mentioned above, selectivity seems to be driven by solubility issues since isolation of the product from the precipitate or from solution results in different enantiose-lectivities. Indeed, this system performs far worse under catalytic conditions. The best result involves the use of silver chloride as reoxidant the heterooxidative coupling of two naphthols 182 and 183 affords the product 184 in 41% yield and 32% ee using 10 mol% catalyst, Eq. 107. 

Oxidation of phenols and aromatic amines using HRP is generally of little synthetic value, as oligomers and polymers are the main products (5, 260). Under certain conditions oxidative coupling of phenols or naphthols to give biaryls can be achieved, but with low selectivity (262). In contrast, HRP can catalyze a number of useful oxidative N-and 0-deaIkyIation reactions that are relatively difficult to carry out synthetically. This area has been described in detail by Meunier (263). A method for the preparation of optically active hydroperoxides using HRP C has been developed (264). Optically pure (S)-hydroperoxides... 

The phenolic oxidative coupling process can also be demonstrated in laboratory experiments. Thus, treatment of 1-naphthol with alkaline potassium... 

We have found that the novel chiral self-dimerizahon of V complexes produces an active unsaturated structure with a new chiral conformation on a Si02 surface, and provides highly enanhoselective achve sites for the asymmetric oxidative coupling of 2-naphthol [35, 36]. Table 10.3 summarizes catalyhc activities, selectivities and enantiomeric excess (e.e.) of homogeneous and heterogeneous V catalysts for the oxidative coupling of 2-naphthol. The homogeneous reactions on a representative L-leucine based V monomer did not exhibit the catalyhc activity. Only in the presence of chlorotrimethylsilane as an acidic promoter did the reachon proceed, but conversion was as low as 15% at 293 K, selectivity to BINOL and e.e. to (P)-BINOL were quite low at 73% and 8%, respectively (Table 10.3). Furthermore, loss of activity occurred and no reachon proceeded after 9 days. 

Table 10.3 Catalytic activities, selectivities and enantiomeric excess (e.e.) in homogeneous and heterogeneous vanadium (V) catalyses for the oxidative coupling of 2-naphthol .

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. 

There are no reports of chiral complex catalysts that could catalyze the aerobic oxidative coupling of 2-naphthol at a reasonable reaction rate with high enantioselectivity. The reactions mentioned above are accomplished in 24 h or in 7-10 days. These drawbacks should be overcome in the near future. 

CatalyticaUy oxidative coupling of 7-Alkoxy-l-naphthols by chiral... 

ENANTIOSELECTIVE OXIDATIVE COUPLING OF 2-NAPHTHOLS CATALYZED BY A NOVEL CHIRAL VANADIUM COMPLEX... 

CATALYTIC OXIDATIVE COUPLING OF 7-ALKOXY-l-NAPHTHOLS BY CHIRAL VANADIUM COMPLEXES... 

Table 8.1 Oxidative coupling of 2-naphthols using catalyst 1...

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. 

Catalysis in reaction systems with undissolved substrates and products is not restricted to biocatalysis. High yields in sobd-state synthesis, sohd-to-sohd reactions, and solvent-free systems have also been reported for aldol condensation, Baeyer-Villiger oxidation, oxidative coupling of naphthols, and condensation of amines and aldehydes [1, 2]. 

Systems based on the reaction of iron salts with heterocyclic hydrazines and on the oxidative coupling of 2-aminothiazoles with naphthols have also been used (64USP3129109). In a similar process a heterocyclic hydrazone, such as the benzothiazole (174), is cleaved in the presence of an oxidizing agent, and the resulting oxidation products react immediately to give an azo dye (175) (62USP3076721). 

Dehydrogenation reactions of ketones have been applied to the aromatization and oxidative coupling of polycycles. High temperature dehydrogenation of 7-fluoro-3,4-dihy-dronaphthalen-l(2/7)-onc with sulfur gives 7-fluoro-1-naphthol in 90% yield.196 During the oxidation of fluorinated anthraccn-9(10//)-one 9 with iron(III) chloride, a radical is formed that collapses by a termination reaction to give the bianthryl derivative 10.197... 

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

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