Oxidation at the sulfur atom

Diaryl-thiazolidin-4-one 5,5-dioxides 162 were obtained by reacting thioglycolic acid with Schiff bases, followed by oxidation at the sulfur atom... 

The proton spectra of thietane oxide (5a) and thietane dioxide (5b) have been studied in order to evaluate whether the oxidation at the sulfur atom changes the established 35° puckering of the ring218, and whether a correlation is possible between structure and... 

Many organosulfur compounds undergo biological oxidation at the sulfur atom to yield products which have pronounced physiological activity or serve as intermediates in generating bioactive compounds. Three examples are the lachrymating agent in onions ( ) (1), the oxo intermediate ( ) in metabolic desulfuration of phosphorothionate insecticides to form potent cholinesterase inhibitors (2), and the sulfoxides QJ produced on metabolism of thiocarbamate herbicides (3). 

The main route of metabolism of febantel in rats, sheep, and cattle appears to be cyclization to yield fenbendazole. Oxidation at the sulfur atom can also occur to yield febantel sulfoxide, which then undergoes cyclization to give oxfendazole. Both fenbendazole and oxfendazole can then undergo further metabolism. 

Oxidation at the sulfur atom of thiadiazole to the mono-oxide (157) causes a loss in aromatic character which can be seen by X-ray analysis and by the 33 kcal mol1 inversion barrier of the pyramidal sulfur which agrees with the calculated barrier (31.9 kcal mol-1) (82JA1375). 

Thiazines can be oxidized at the sulfur atom to give sulfoxides and eventually sulfones. Generally speaking, however, this is not a good approach to these structures as there are inherent problems of non-selectivity and over-oxidation. Air oxidation is sufficient to convert the 1,3-benzothiazine (24 R = alkoxy) into the 1-oxide (25 n = 1), whereas potassium permanganate yields the 1,1-dioxide (25 n = 2). In the case of the unsubstituted compound (24 R = H) the sulfur atom is less reactive and oxidation affords the l,3-benzothiazin-4-one (26) (77ACH(92)317). 

Sulfides are generally oxidized much faster than olefins. For example, with r-BuOjH-VO(acac)2 in ethanol at 25°C, the relative rates decreased in the order Bu"S(100) > PhSBu"(58) >Bu"SO (1.7) > cyclohexene (0.2).480 Unsaturated sulfides are selectively oxidized at the sulfur atom as shown in the following example477 ... 

Successive oxidation at the sulfur atom occurs with formation of the sulfoxide followed by elimination of sulfite to yield either 2-hydroxy-biphenyl (Omori et al. 1992) or benzoate (van Afferden et al. 1990) (Figure 6.54). The pathway for the formation of 2-hydroxybiphenyl... 

Lowering the temperature of the reaction to — 50 ° did not have a profound effect on the stereochemical control of oxidation at the sulfur atom we obtained the two sulphoxides in a 85 15 ratio. It was thought that the conformation of the macrocycle might induce a stereoselectivity during the oxidation via a com-plexation of m-chloroperbenzoic acid with the molecule. Excess sodium bicarbonate in suspension was added to the reaction medium in order to remove m ta-chlorobenzoic acid formed and thus, favor an association between the peracid and the amino function of the chain. The reaction, performed at — 50 ° in order to avoid oxidation of the nitrogen atom, gave rise to a mixture of the two isomers in 95 5 ratio. 

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