Desulfination

In the fourth and final step, the intermediate 2-(2,-hydroxyphenyl)ethen-l-sulfmate (HPESi ) is desulfinated to 2-(2 -hydroxyphenyl)ethan 1-al (HPEal). As seen from Fig. 4, this step cannot be catalyzed by the arylsulfinate desulfinase like DszB. Instead, the enzyme has to be an alkenylsulfmate desulfinase. The alkenyl C-S bond as present in the intermediate, can only be desulfurized by hydroxylase-type enzyme, giving an enol, which can then tautomerize to HPEal and sulfite. However, the identity of the sulfur-containing product has not been confirmed [34],... 

The amount of Lewis acid to be used is depicted as an effective amount and a minimum limit of 0.5 mole equivalent with respect to the sulfmated compound concentration was mentioned. A wide variety of Lewis acids was mentioned to be useful for the present invention in the patent document, but only copper (II) compounds were claimed. The way in which the Lewis acid is used (either as a homogeneous or a heterogeneous phase), was reported to be irrelevant. So, it could be employed in solution in the reaction medium or insoluble as powders or on a solid support, such as alumina or a zeolite. The Lewis acid is supposed to be acting as a catalyst in the desulfination process. The temperature and pressure conditions for this reaction are substantially higher than the microbial conditions. The temperature and pressure conditions did not form part of any claim, but the document stipulates values between 50°C and 100°C, and 10 and 15psi, respectively. The quantitative effectiveness or conversion values of this reaction were not given, but it looks like it would diminish the advantages of a biocatalytic process. 

This enzyme [EC 4.1.1.12], also known as desulfinase, catalyzes the conversion of aspartate to alanine and carbon dioxide. Pyridoxal phosphate is a required cofactor. The enzyme will also catalyze the decarboxylation of aminomalonate as well as the desulfination of 3-sulfino-alanine to sulfite and alanine. 

Scheme 20. Desulfination reactions. (A) acid-catalyzed zwitterion mechanism, (B) Se2 mechanism.

The reaction of sulfinyloxirane 130 with n-C4H9Li takes place at the sulfinyl group to afford the desulfinated epoxide 133 in good yield. This reaction proceeds at — 100°C with concomitant formation of phenyl n-butyl sulfoxide 132. Thus, oxiranyllithium 131 picks up the acidic proton of the in situ formed 132 to generate the reduce epoxide 133 (equation 46) . 

Due to their inherent polarizability, a-halo-/3-ketosulfoxides may be used as electrophilic partners in desulfination reaction to generate metal enolate. Therefore, treatment of a-halo-/3-ketosulfoxides with EtMgBr gives magnesium enolates. Trapping these reagents with various electrophiles allows the preparation of a-haloketones (equation 79, Table 10). 

This effect cannot be explained by simply considering differences in frontier orbital energies. A useful monofluorinated dienophile has been prepared [364] using metallated difluoroenol carbamate chemistry (Eq. 143) cycloaddition occurred smoothly with a range of dienes, and desulfination could be achieved under mild conditions without loss of the fluorine atom. Wakselman and co-workers [365] synthesised a rare competent difluorinated dienophile. Lewis acid catalysed Diels-Alder reaction with furan afforded an acceptable yield of (unfortunately) unstable cycloadduct which decomposed to a phenolic product via a dehydrofluorination reaction, circumscribing its utility (Eq. 144). 

To systematize the nomenclature of these processes, the eliminations of SO2 and SO3 are termed desulfination (from sulfinate) and desulfonation (from sulfonate), respectively. 

No desulfination has been reported for metal [Pg.56]

The desulfination of the metal-vinyl products containing a sultine... 

Surveyed in this section are known SOg insertion and desulfination reactions. Kinetic and stereochemical results already discussed in Sections III-V, as well as the cycloaddition processes treated in Section V, have been given a cursory mention for the sake of completeness. The insertion reactions involving bonds other than M—C are omitted. Also excluded are all aspects of the chemistry of metal sulhnate complexes except sulfur dioxide insertion and desulfination. Readers interested in alternative methods of synthesis and in the physical and chemical properties of these and related compounds are referred to a recent review 128). 

Neither SO2 insertion nor desulfination studies have been reported for these elements. 

The alkyls CpMo(CO)3R (R = Me, Et, and CHaPh) readily insert SOa (57) these reactions were the subject of a kinetic study (71, 76). When R = CHaPh, the 0-sulfinato intermediate was detected spectroscopically (72, 73). Contrasting with the above behavior is the apparent lack of reactivity of CpMo(CO)3CFa (57) and CpMo(CO)3CHaCN (124) toward neat SOa- However, the dicarbonyl CpMo(CO)a(PPh3)Me does afford the corresponding >S -sulfinate, the reaction proceeding much more rapidly than that of its parent tricarbonyl, CpMo(CO)3Me (57). The photochemically induced desulfination of CpMo(CO)3S(0)a-CHaPh furnishes CpMo(CO)3CHaPh (35% yield) in contrast, irradiation of CpMo(CO)3S(0)aMe yields [CpMo(CO)3]a (57). 

Sulfur dioxide extrusion has been reported only for CpFe(CO)aS-(0)aCeF5 [Eq. (32)], This desulfination can be effected either photo-chemically or thermally in toluene at reflux (43). Other CpFe(CO)aS-(O)aR complexes [R = CCI3 43), Me, CHaPh, and Ph (JJ)] resist loss... 

A study was reported on the desulfination of some arenesulfonyl halides, RSOaX, using Ru(PPh3)3Cla 15). 

The catalytic desulfination of several arenesulfonyl halides has been studied using Rh(PPh3)aCl and Rh(CO)(PPh3)aCl (15). 

The reaction of palladium(II) complexes with arenesulfinic acids or their salts to yield the organic biaryls appears to proceed by formation of palladium sulhnato compounds and their desulfination 53a). 

Electronegative substituents promote the reaction e.g., desulfination of YCgF4S02Li with HgX2 proceeds at RT . Either mono- or diorganomercurials can be obtained ... 

HC(OH)CH(HgCl)(CH2)3CH2 Reaction with R2CN2 5.7.2.3.3 C Hi.CIHgOjS cyclo-C HiiSOjHgCl Desulfination 5,7,2,3,7 C HijCljLiSi... 

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