Thioethers sulfoxides

G. Boche, The Structure of Lithium Compounds of Sulfones, Sulfoximides, Sulfoxides, Thioethers and 1,3-Dithianes, Nitriles, Nitro Compounds and Hydrazones, Angew. Chem. Int. Ed. Engl. 1989, 28, 277-297. 

Key words Amino acids. Catalytic oxidation under ambient conditions, 2-chloroethyl ethyl sulfide, Co-catalysis by copper. Decontamination, Effect of ligands, Gold complexes. Mustard gas, Perfluorinated solvents. Solvent effect. Sulfoxide, Thioether... 

Figure 3-17. Consecutive application of two reaction schemes to model the oxidation of thioethers to sulfoxides.

Clearly, for symmetry reasons, the reverse process should also be considered. In fact, early versions of our reaction prediction and synthesis design system EROS [21] contained the reaction schemes of Figures 3-13, 3-15, and 3-16 and the reverse of the scheme shown in Figure 3-16. These four reaction schemes and their combined application include the majority of reactions observed in organic chemistry. Figure 3-17 shows a consecutive application of the reaction schemes of Figures 3-16 and 3-13 to model the oxidation of thioethers to sulfoxides. 

The classical structures of pyrrole, furan and thiophene (31) suggest that these compounds might show chemical reactions similar to those of amines, ethers and thioethers (32) respectively. On this basis, the initial attack of the electrophile would be expected to take place at the heteroatom and lead to products such as quaternary ammonium and oxonium salts, sulfoxides and sulfones. Products of this type from the heteroaromatic compounds under consideration are relatively rare. 

Sulfonyloxaziridines were recently proposed as O-transferring reagents. Oxaziridine (89) converted thioethers to sulfoxides (90) and diaryl disulfides into their 5-oxides (91) (78TL5171). Epoxidations are also possible (81TL917). 

Two-component methods represent the most widely applied principles in sulfone syntheses, including C—S bond formation between carbon and RSOz species of nucleophilic, radical or electrophilic character as well as oxidations of thioethers or sulfoxides, and cheletropic reactions of sulfur dioxide. Three-component methods use sulfur dioxide as a binding link in order to connect two carbons by a radical or polar route, or use sulfur trioxide as an electrophilic condensation agent to combine two hydrocarbon moieties by a sulfonyl bridge with elimination of water. 

The most widely applied method to prepare sulfones is the oxidation of thioethers. In the course of these oxidations sulfoxides must occur as intermediates. However, since oxidation mechanisms for thioethers and sulfoxides are partly different, these oxidations will be discussed separately. A recently published method337,338 allows oxidation of a... 

Table 11 affords a survey on oxidation methods of thioethers and sulfoxides. 

TABLE 11. Oxidation of thioethers and sulfoxides by various methods... 

Surprisingly there are relatively few data on the cathodic or anodic behaviour of sulfoxides 77. It is quite interesting to consider that the sulphoxide function is intermediate between the corresponding thioether and sulphone. Thus data concerning the cathodic properties of sulphoxides derive both from the basicity of the S=0 group and from their capability to allow the formation of the corresponding thioether, while cleavage reactions on the C—S bond are quite unusual. On the other hand, oxidation may provide sulphones. 

Selenides (R2Se) can be oxidized to selenoxides and selenones. It is possible to oxidize a thioether to a sulfoxide in the presence of an alcohol moiety using MnOa/HCl. ... 

Thiols, thioethers and sulfoxides [37-39] e.g. sulfur-containing amino acids... 

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