2-naphthol derivatives, catalytic oxidative

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

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. 

Based on their mechanistic investigation on the Cu -mediated oxidative coupling of 2-naphthol derivatives, Smrcina, Kocovsky, and co-workers were able to develop the first catalytic asymmetric oxidative biaryl coupling reaction (Scheme 3.3). AgCl was used as the stoichiometric oxidant to regenerate the Cu species. In order to avoid the formation of detrimental HCl by-product, the corresponding sodium 2-naphthol salts were employed as the coupling partners. The desired product 3 was obtained in 41% yield (8 turnovers) with 32% ee. 

Scheme 9.10 Catalytic and enantioselective oxidative coupling of 2-naphthol derivatives using vanadium(iv) complexes, independently reported by Chen and Uang. "...

Scheme 9.19). The enantioselectivity during the polymerisation was estimated to be over 80% enantiomeric excess. During the course of their study on the stereocontrolled synthesis of poly(2,3-dihydroxynaphthalene) by AOCP, Habaue found that the novel system, VO(stearate)2-D-tartaric acid lithium salt, showed a catalytic activity with much higher stereocontrol than that of the above-mentioned vanadyl sulfate-Phbox catalyst. However, Habaue s catalytic system exhibited no activity for the oxidative coupling of other 2-naphthol derivatives. 

Noji, M., Nakajima, M., and Koga, K., A new catalytic system for aerobic oxidative coupling of 2-naphthol derivatives by the use of CuCl-amine complex a practical synthesis of binaphthol derivatives. Tetrahedron Lett., 7983 (1994). 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

Nakajima et al. (128) found that a number of diamines functioned as moderately effective ligands for Cu(II) in the catalytic aerobic oxidation of 2-naphthols. A series of proline derivatives were evaluated with the aniline ligand 187 providing optimal selectivities. Unfortunately, 2-naphthol affords only racemic binaphthol. With an isolated catalyst, formulated as 187 Cu(OH)Cl in analogy to the known TMEDA Cu(OH)Cl (TMEDA = A,A,A,A-tetramethylethylenediamine), oxidative... 

Oxidative dimerisation of 2-naphthols to l,l -bis-2,2 -naphthol (BINOL) derivatives has been studied extensively. Copper(ii) catalyst under molecular oxygen has shown broad versatility in this transformation. Copper(ii)-Schiff base complexes reveal good catalytic activity in the dimerisation of 2-naphthols with low catalyst loading. This catalyst system is not so effective for substrates bearing electron-withdrawing substituents. " Cu(OH)Cl(TMEDA) is stable and shows good catalytic activity even for electron-poor naphthols... 

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