Oxidative couphng

Peroxidases have been used very frequently during the last ten years as biocatalysts in asymmetric synthesis. The transformation of a broad spectrum of substrates by these enzymes leads to valuable compounds for the asymmetric synthesis of natural products and biologically active molecules. Peroxidases catalyze regioselective hydroxylation of phenols and halogenation of olefins. Furthermore, they catalyze the epoxidation of olefins and the sulfoxidation of alkyl aryl sulfides in high enantioselectivities, as well as the asymmetric reduction of racemic hydroperoxides. The less selective oxidative coupHng of various phenols and aromatic amines by peroxidases provides a convenient access to dimeric, oligomeric and polymeric products for industrial applications. 

Newer types of the dinuclear vanadium(IV) complex catalysts 84 have been developed. The abovementioned dinuclear vanadium complexes possess a VO V linkage whereas the ESR study on the catalyst 84 revealed no V—O—V linkage. The sense of enantioselection by the catalyst 84 of the (R,5,5)-structure is opposite to that of the binuclear complex 78a of the same (R,5,5)-structure. These results suggested two active sites attached to the binaphthyl skeleton in the catalyst 84 performed the dual activation of 2-naphthols in the oxidative couphng to achieve high enantioselectivity ... 

Oxidation indices, 656-72 peroxide determination, 762-3 peroxide value, 656, 657-64 colorimetry, 658-61 definition, 657 direct titration, 657 electrochemical methods, 663-4 IR spectrophotometry, 661-3 NIR spectrophotometry, 663 UV-visible spectrophotometry, 658-61 secondary oxidation products, 656, 665-72 tests for stability on storage, 664-5, 672 thermal analysis, 672 Oxidative amperometiy, hydroperoxide determination, 686 Oxidative cleavage alkenes, 1094-5 double bonds, 525-7 Oxidative couphng, hydrogen peroxide determination, 630, 635 Oxidative damage... 

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]. 

Hooker JM, Esser-Kahn AP, Francis MB. Modification of aniline containing proteins using an oxidative couphng strategy. J. Am. Chem. Soc. 2006 128 15558-15559. 

In some methods, the final mixture is acidified slightly to stop the reaction, and the intensity of the yellow chro-mophore is measured at 400 nm. In stronger acid solution, the color becomes pink, with maximum absorbance at 540 nm, and both sensitivity and stability are improved. Other approaches to measurement of the H2O2 produced include the peroxide-mediated oxidative coupMng of 3-methyl 2-benzothia2olinone hydrazone (MBTH) with N,N-dimethyl-aniline (DMA) catalyzed by peroxidase or the oxidative coupHng of p-aminophenazone (PAP) to phenoi. Both procedures have been automated. The... 

One of the earliest examples of the use of palladium in pyrrole chemistry was the Pd(OAc)2-induced oxidative couphng of TV-methylpyrrole with styrene to afford a mixture of olefins 26 and 27 in low yield based on palladium acetate [33]. 

J Ralph, K Lundquist, G Brunow, F Lu, H Kim, PF Shatz, JM Marita, RD Hatfield, SA Ralph, JH Christensen, W Boerjan. Lignins Natural polymers from oxidative couphngs of 4-hydroxyphenylpropanoids. Phytochem Rev 3 29-60, 2004. 

C. M. Timmers, G. A. van der Marel, and J. H. van Boom, Synthesis of a methyl heptaglucoside with phytoalexin ehdtor activity based on oxidative couphng of glucals, Eur. J. Chem., 1 (1995) 161-164. 

Methane coupUng chemistry has been reported [112, 113] in mixed conducting membranes of Bij 5Y0 3Smo 2O3. CoupHng selectivities as high as 54% and yields of 35% were obtained at 900 °C. The simultaneous oxidative coupHng of methane and oxidative dehydrogenation of ethane over a basic catalyst system has been reported [114], as well as the use of carbon dioxide as an oxidant in the methane/ ethane system[115]. In the latter case, ethylene content of up to 16% was obtained in the tail gas. 

Bis-oxazohne Hgands can also be produced by oxidative coupHng of the copper derivative of diastereoisomerically pure 28 (Scheme 11) [37]. Further Hthia-tions of the product 39, which was produced as single diastereoisomer, occur (as... 

Synthesis of TT-extended porphyrins via intramolecular oxidative couphng 12CC10069. 

Oxidative coupHng between two C—H bonds is a rather young but rapidly evolving area within C—H activation. Similar to C—H/C—X cross-coupling reactions, regioselectivity stays one of the major challenges for direct functionalization of heterocycles. As in CDC, more reaction sites are involved and the complexity in this respect is in fact even higher. 

In connection with our project related to peptidomimetics, we had the occasion to examine the U-4CR of N-methyl-hydroxylamine 105a (R= Me), heptanal, benzylisocyanide 106a, and acetic acid, developed earlier by Guanti and coworkers [54]. Under the conditions used by the above authors (MeOH, rt), we did obtain the expected U-4CR adduct 107a (R=Me) and the nonacylated adduct 108a (R=Me) in yields of 45% and 18%, respectively (Scheme 15.30). However, N-benzyl-2-oxoheptanamide 109 was also produced unexpectedly in 10% isolated yield. The formation of 109 represented a formal oxidative couphng of aldehyde and isocyanide [55]. 

Haag S, van Veen A C and Mirodatos C (2007), Influence of oxygen supply rates on performances of catalytic membrane reactors application to the oxidative couphng of methane , Catal Today, 127,157-164. 

Lu Y P, Dixon A G, Moser W R, Ma Y H and Balachandran U (2000a), Oxidative couphng of methane using oxygen-permeable dense membrane reactors , Catal Today, 56,297-305. 

Oxidative couphng of aromatic compounds via the Scholl reaction has been successfully apphed to the sjmthesis of a polyarylethersulfone [12], High-molecular-weight polymer was obtained by treating 4,4 -di(l-napthoxy)diphenylsulfone and 4,4 -di(napthoxy)benzophenone with ferric chloride. Equimolar amounts of the Lewis acid were used to effect the polymerization. This synthesis route is limited in scope and utihty as it is only apphcable to naphthoxy-based monomers and other systems that can undergo the SchoU reaction. 

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