Sulfoxide catalysts

Cyclohexanone and Cyclopentanone Monooxygenases as Baeyer-Villigerases and Sulfoxidation Catalysts... 

The development of the single enantiomer azole within the family of compounds used for gastrointestinal treatments is exemplified by Astra-Zeneca s Esomeprazole (a potent gastric acid secretion inhibitor) (Eigure 1.54). This development gave the impetus for the search for industrial chiral sulfoxidation catalysts. 

Another excellent example of allylic C—H alkylation has been developed using a Pd (OAc)2-bis-sulfoxide catalyst (Equation 11.8) [19]. Bis-sulfoxide is a crucial and efficient ligand for the transformation. The regioselectivity of the allylation reactions is controlled by steric effects. The synthetic utility of this method is highlighted by the subsequent transformation of its product. 

Uemura et al. found that the combination Ti(OPr%/binaphthol/water in ratio 1 2 >10 acts as a catalyst for oxidation of aryl methyl sulfides into the corresponding sulfoxides by Bu OOH (see also Section 1.4.1) [159]. A mechanistic study showed that the titanium complex was a sulfoxidation catalyst (initial ee -50%) as well as a catalyst for the overoxidation into sulfones, with an enhancement of the ee of the residual sulfoxides (because the minor sulfoxide enantiomer is preferentially oxidized). In a subsequent paper, the authors reported the kinetic resolution of racemic aryl methyl sulfoxides by the same catalyst [160]. A stereoselectivity factor s of 2.6 was calculated for the kinetic resolution of racemic methyl p-tolyl sulfoxide. For example, methyl p-tolyl sulfoxide (<99% ee) could be recovered from oxidation at about 75% conversion. Using partially resolved l,l -binaphthol, a positive nonlinear effect was established. 

Recently, several groups have reported catalysts for the Oa-based oxidation of sulfides that are both fairly fast and selective. Bosch and Kochi established that NO2 is a highly effective sulfoxidation catalyst (, 5), as is NO however, gases are not compatible with the formulation of useful self-decontaminating solutions, fabrics, cosmetics, filters or coatings. Other published catalysts for aerobic sulfoxidation are corrosive, toxic, require light, or exhibit other characteristics we wish to avoid. 

The activities of other nitrate-containing sulfoxidation catalysts were also evaluated. The known sulfide oxidation catalysts (NH4)2Ce (N03)6 (/7) (entry 7) and titanium nitrate (entry 8) have moderate activity. The data demonstrate the essential role of both nitrate and proton in the catalytic, aerobic oxidation of the sulfide CEES. 

Bonchio, M., Licini, G Modena, G., Moro, S Bortolini, O., Traldi, P., and Nugent W.A. (1999) Enantioselective Ti(IV) sulfoxidation catalysts bearing C3-symmetric trialkanolamine ligands solution speciation by H NMR and ESI-MS analysis. /. Am. Chem. Soc.,... 

The selective oxidation of sulfides to sulfoxides is an important reaction in biological systems, ft is a well-studied model reaction for oxo atom transfer and it is of importance for applications in pharmaceutical and preparative organic chemistry [1, 2, 60]. Iron- and ruthenium-based sulfoxidation catalysts have also been explored in the area of asymmetric synthesis and enantioselective catalysis... 

More recently, Bolm developed a new asymmetric sulfoxidation catalyst based on the employment of Fe(III) as the metal center with a Schiff base chiral ligand 26 in the presence of H2O2 as the atom-efficient terminal oxidant (Scheme 48.12). The catalytic system with examples of its activity and selectivity is reported in Scheme 48.11. Optimization of the ligand 26 and screening of a series of aromatic carboxylic acids 27 and salts as promoters for the oxidation of sulfides 28 led to a marked increase in the yield of sulfoxide 29 when employing electron-rich benzoic acids, with a further increase also on the stereoselectivity. As an example, in the oxidation of phenyl methyl sulfide. 

The widely used Moifatt-Pfltzner oxidation works with in situ formed adducts of dimethyl sulfoxide with dehydrating agents, e.g. DCC, AcjO, SO], P4O10, CCXTl] (K.E, Pfitzner, 1965 A.H. Fenselau, 1966 K.T. Joseph, 1967 J.G. Moffatt, 1971 D. Martin, 1971) or oxalyl dichloride (Swem oxidation M. Nakatsuka, 1990). A classical procedure is the Oppenauer oxidation with ketones and aluminum alkoxide catalysts (C. Djerassi, 1951 H. Lehmann, 1975). All of these reagents also oxidize secondary alcohols to ketones but do not attack C = C double bonds or activated C —H bonds. 

Phosphoms pentafluoride behaves as a Lewis acid showing electron-accepting properties. It forms complexes, generally in a ratio of 1 1 with Lewis bases, with amines, ethers, nitriles, sulfoxides, and other bases. These complexes are frequently less stable than the similar BF complexes, probably owing to stearic factors. Because it is a strong acceptor, PF is an excellent catalyst especially in ionic polymeri2ations. Phosphoms pentafluoride is also used as a source of phosphoms for ion implantation (qv) in semiconductors (qv) (26). 

Reaction takes place ia aqueous solution with hydrogen peroxide and catalysts such as Cu(II), Cr(III), Co(II), ferricyanide, hernia, or peroxidase. Chemiluminescent reaction also takes place with oxygen and a strong base ia a dipolar aprotic solvent such as dimethyl sulfoxide. Under both conditions Qcis about 1% (light emission, 375—500 am) (105,107). 

Trilialophenols can be converted to poly(dihaloph.enylene oxide)s by a reaction that resembles radical-initiated displacement polymerization. In one procedure, either a copper or silver complex of the phenol is heated to produce a branched product (50). In another procedure, a catalytic quantity of an oxidizing agent and the dry sodium salt in dimethyl sulfoxide produces linear poly(2,6-dichloro-l,4-polyphenylene oxide) (51). The polymer can also be prepared by direct oxidation with a copper—amine catalyst, although branching in the ortho positions is indicated by chlorine analyses (52). 

VL few, inexpensive not stoichiometric requires catalyst sulfoxidation of paraffins ... 

Fluorinated and Ghlorfluorinated Sulfonic Acids. The synthesis of chlorinated and fluorinated sulfonic acids has been extensively reviewed (91,92). The Hterature discusses the reaction of dialkyl sulfides and disulfides, sulfoxides and sulfones, alkanesulfonyl haHdes, alkanesulfonic acids and alkanethiols with oxygen, hydrogen chloride, hydrogen fluoride, and oxygen—chloride—hydrogen fluoride mixtures over metal haHde catalysts, such as... 

Esters derived from the primary alcohols are the most stable and those derived from the tertiary alcohols are the least stable. The decomposition temperature is lower in polar solvents, eg, dimethyl sulfoxide (DMSO), with decomposition occurring at 20°C for esters derived from the tertiary alcohols (38). Esters of benzyl xanthic acid yield stilbenes on heating, and those from neopentyl alcohols thermally rearrange to the corresponding dithiol esters (39,40). The dialkyl xanthate esters catalytically rearrange to the dithiol esters with conventional Lewis acids or trifluoroacetic acid (41,42). The esters are also catalytically rearranged to the dithiolesters by pyridine Ai-oxide catalysts (43) ... 

Cellulose dissolved in suitable solvents, however, can be acetylated in a totally homogeneous manner, and several such methods have been suggested. Treatment in dimethyl sulfoxide (DMSO) with paraformaldehyde gives a soluble methylol derivative that reacts with glacial acetic acid, acetic anhydride, or acetyl chloride to form the acetate (63). The maximum degree of substitution obtained by this method is 2.0 some oxidation also occurs. Similarly, cellulose can be acetylated in solution with dimethylacetamide—paraformaldehyde and dimethylformamide-paraformaldehyde with a potassium acetate catalyst (64) to provide an almost quantitative yield of hydroxymethylceUulose acetate. 

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