Catalysis sulfoxidation

The catalytic effect of aromatic nitro groups in the substrate and product or in an added inert nitro compoimd (e.g., w-dinitrobenzene in 18) has been observed in the reaction of 2,4-dinitrochlorobenzene with an amine in chloroform. Hydrogen bonding to benzil or to dimethyl sulfone and sulfoxide also provided catalysis. It is clear that the type of catalysis of proton transfer shown in structure 18 will be more effective when hydrogen bonding is to an azine-nitrogen. 

Treatment of pre-dried natural starting materials with compressed gases (propane and/or butane) and organic solvents to facilitate complete extraction Heating pre-treated lutein-containing material in mixture of aqueous solution, alkali hydroxide, and dimethyl sulfoxide/organic solvent under catalysis at 50 to 120 C... 

Kielbasinski, P., Rachwalski, M., Mikolajczyk, M. et al. (2007) Enzyme-promoted desymmetrisation of prochiral bis(cyanomethyl) sulfoxide. Advanced Synthesis and Catalysis, 349, 1387-1392. 

In addition to the catalysis of sulfoxide deoxygenation (Section IV,C) and sulfoxide oxygenation (Section IV,D), other interesting reactions have been shown to be catalyzed by sulfoxide complexes, and these are detailed below. 

The iodohydroxylation of 1,2-allenyl sulfoxide 171 with I2 in the presence of H20 exhibits E-selectivity leading to (E)-2-iodo-3-hydroxy-l-alkenyl sulfoxide [88]. By using Br2, CuBr2 or NBS, (E)-2-bromo-3-hydroxy-l-alkenyl sulfoxide is produced. For the chlorohydroxylation of a sulfoxide, CuCl2 and silica gel were used to mix with the sulfoxide to deliver the (E)-chlorohydroxylation products highly stereoselec-tively [88]. The chirality in the allene moiety can be efficiently transferred to the final allylic alcohols. Under the catalysis of a Pd or Ni complex, the C-X and C-S bonds can be coupled to introduce different substituent(s) into the different locations of the C=C bond. 

Under the catalysis of tBuOK in tBuOH, a hydroxyl group can also attack intramo-lecularly to the central carbon atom, which was followed by C=C bond migration leading to cyclic vinylic sulfoxides 192 (Scheme 10.87) [97]. 

As shown in Table 12,H202 and fBuOOH have been used frequently as oxygen donors in peroxidase-catalyzed sulfoxidations. Other achiral oxidants, e.g. iodo-sobenzene and peracids, are not accepted by enzymes and, therefore, only racemic sulfoxides were found (c.f. entries 34-36). Interestingly, racemic hydroperoxides oxidize sulfides to sulfoxides enantioselectively under CPO catalysis [68]. In this reaction, not only the sulfoxides but also the hydroperoxide and the corresponding alcohol were produced in optically active form by enzyme-catalyzed kinetic resolution (cf. Eq. 3 and Table 3 in Sect. 3.1). 

The kinetics of oxidation of several para-substituted anilines and aliphatic acetals by peroxomonosulfate in aqueous acetic acid have been investigated. In the oxidation of sulfides to sulfoxides by peroxymonosulfate (Oxone), the observed increase in second-order rate constants with increasing concentration of H2SO4 has been shown to be due to the increasing polarity of the medium, rather than to acid catalysis. Similar conclusions were arrived at for the oxidation of aryl thiobenzoates and thiol-phosphorus(V) esters. 

Balance of Activatlon/DetoxifIcatlon Reactions. The activated intermediates or reactive fragments appear to be carbamoyl sulfoxides or mono-, dl- and trlchloroacroleins, all of which are relatively unstable compounds. The carbamoyl sulfoxides are rapidly detoxified by reaction with GSH, involving catalysis by a GSH -transferase in the case of -alkyl and -benzyl thiocarba-mate sulfoxides ( -5, 24) but probably not with -chloro-... 

Compound 264 is unexpectedly stable against light, but can easily be oxidized to the sulfoxide 265 and the sulfone 266. Sulfoxide 265 can be isolated and a-activated by reaction with acetic anhydride (Scheme 4.46). a-Acetoxylated tetrahydrothio-phene 267 has 0,S-acetal-like reactivity and can be functionalized with various alcohols or thiols under acid catalysis with camphorsulfonic acid (CSA) (268). 

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