Thioanisole, oxidation

Thioanisole, oxidation, by dinitrogen tetroxide, 46,80 by hydrogen peroxide, 46, 80 by lead tetraacetate, 46, 80 reaction with sodium metaperiodate to form methyl phenyl sulfoxide, 46,78... 

The synthesis of rofecoxib can be achieved by several different routes (Drugs Fut., 1998). A highly efficient synthesis for rofecoxib was recently described (Therien et al., 2001). As illustrated in Scheme 79, acetophenon (i) is prepared according to the literature, by Friedel-Crafts acylation with thioanisole. Oxidation with MMPP (magnesium monoperoxyphthalate hexahydrate) affords the sulfone (ii), which is reacted with bromine in chloroform in the presence of a trace amount of AICI3, to give (iii). Bromoketone (iii) is than coupled and cyclized in a second step, one-pot procedure with phenylacetic acid. Firstly, the mixture of bromoacetophenone (iii) and phenylacetic acid in acetonitrile is treated with... 

Figure 12. Rates and enantioselectivity of thioanisole oxidation catalyzed by H64D/V68X Mb mutants.

The initial turnover number of the thioanisole oxidation by the reconstituted Mb is clearly larger than that observed for the native Mb, and the kcat/Km value is more than seven fold higher than that of the native protein. The epoxidation of styrene is also effectively catalyzed by the reconstituted Mb by 10-fold increase compared to native Mb. These findings indicate that the appropriate modification of the heme propionate side chains forms a substrate-binding domain that enhances the peroxidase and peroxygenase activities of Mb, as shown in Table VI. 

Mc3SiBr, thioanisole." This reagent combination also cleaves a car-bobenzoxy (Z) group and a 4-MeOC6H4CH2SR group and reduces sulf- oxides to sulfides. 

Figure 7.32 Biocatalytic oxidation of thioanisole to (5)-methy 1-phenyl-sulfoxide...

Pezzotti, F. and Therisod, M. (2007) Enantioselective oxidation of thioanisole with an alcohol oxidase/ peroxidase bienzymatic system. Tetrahedron Asymmetry, 18 (6), 701-704. 

Perfiuoroolefins, 0-substituted, from a-trifluoromethyl ketones, 48,119 Periodate oxidation of thioanisole, 46, 78... 

Thioanisole (MPS) oxidation with 30% aqueous H2O2 over Ti-SBA-15 and other Ti,... 

For the dehydrogenation of CH—XH structures, for example, of alcohols to ketones, of aldehydes to carboxylic acids, or of amines to nitriles, there is a wealth of anodic reactions available, such as the nickel hydroxide electrode [126], indirect electrolysis [127, 128] (Chapter 15) with I , NO, thioanisole [129, 130], or RUO2/CP [131]. Likewise, selective chemical oxidations (Cr(VI), Mn02, MnOJ, DMSO/AC2O, Ag20/Celite , and 02/Pt) [94] are available for that purpose. The advantages of the electrochemical conversion are a lower price, an easier scale-up, and reduced problems of pollution. 

Furthermore, a double mediatory system consisting of alkyl methyl sulfide and bromide ion was developed, which made the oxidation of alcohols feasible at a lower potential (1.1 V vs SCE) than that of thioanisole (1.60 V vs SCE) [45]. Both the alkyl methyl sulfide and the bromide ion act together as mediators. Under this condition 2-octanol was oxidized to 2-octanone in 85% yield. 

Scheme 25 Oxidation of secondary alcohols with thioanisole as organic redox catalysts.

The oxidation of secondary alcohols (66) to (67) is possible by indirect electrooxidation utilizing thioanisole as an organic redox catalyst in a PhCN-2,6-lutidine-Et4NOTs-(C/Pt) system at 1.5 V vs. SCE (Scheme 25) [81] and is also performed in the presence of 2,2,2-trifluoroethanol [82]. It is suggested that the initially formed cation radical sulfide species derived from the direct discharge of the sulfide provides phenylmethyl-alkoxysulfonium ions, which are transformed to (67) and thioanisole. 

Ionic liquids can be used as co-solvents for CPO-catalysed sulfoxidation. Table 11.1 gives details about different ionic liquids. The procedure is very easy to reproduce and the oxidation of thioanisole proceeds with high chemo- and stereo-selectivity. 

The oxidative degradations of binuclear azaarenes (quinoline, isoquinoline, and benzodrazines) by hydroxyl and sulfate radicals and halogen radicals have been studied under both photochemical and dark-reaction conditions. A shift from oxidation of the benzene moiety to the pyridine moiety was observed in the quinoline and isoquinoline systems upon changing the reaction from the dark to photochemical conditions. The results were interpreted using frontier-orbital calculations. The reaction of OH with the dye 3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-(l,8)(2//,5//)-acridinedione has been studied, and the transient absorption bands assigned in neutral solution.The redox potential (and also the pA a of the transient species) was determined. Hydroxyl radicals have been found to react with thioanisole via both electron transfer to give radical cations (73%) and OH-adduct formation (23%). The bimolec-ular rate constant was determined (3.5 x lO lmoU s ). " ... 

In the photochemical one-electron oxidation of aromatic sulfides, dimer radical cations were formed in rapid equilibrium with monomeric radical cation (59). The complex formation of a- and tt-types has been shown to be sensitive to the steric and electronic influence of substituent. For the case of jo-(methylthio)anisole the formation of TT-type dimer was shown to be reduced due to steric hindrance of two methyl groups. No formation of dimer radical cation was observed for jo-(methoxy)thioanisole and diphenyl disulfide where the corresponding monomer radical cations are stabilized by the delocalization of positive charge on the sulfur atom. Density-functional calculations supported the experimental results. The intramolecular formation of similar radical... 

Shono et al. (1979) recommend the use of thioanisole as a catalyst that allows lowering the electrode potential in the oxidation of the secondary alcohols into ketones. The cation-radical of thioanisole is generated at a potential of up to +1.5 V in acetonitrile containing pyridine (Py) and a secondary alcohol. (The background electrolyte was tetraethylammonium p-toluene sulfonate.) Thioanisole is recovered and, therefore, a ratio of RXR )CHOH PhSMe = 1 0.2 is sufficient. The yield of ketones depends on the nature of the alcohol and varies from 70 to 100%. 

An alternative method for coupling enzymes is to employ a mixed enzyme bioreactor Pezzotti and Therisod [60] reported a bienzymatic system in which alcohol oxidase and peroxidase were coupled to effect the enantioselective oxidation of the sulfide thioanisole (Scheme 3.4). Here, the peroxidase from Coprinus dnereus was mixed with a crude extract of Pichia pastoriz alcohol oxidase and the two enzyme mixture was successfully used to convert gram quantities of thioanisole enantiose-lectively to S-methyl-phenyl-sulfoxide with an enantiomeric excess of 75%. 

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