Diaryl sulphones reactions

Olah and coworkers56 found that treatment of dialkyl, arylalkyl and diaryl sulphides with nitronium hexafluorophosphate (or tetrafluoroborate) 32 at —78° in methylene chloride resulted in the formation of sulphoxides in moderate to high yields (Table 3). In the oxidation of diphenyl sulphide which affords diphenyl sulphoxide in 95% yield, small amounts of the ring nitration products (o- and p-nitrophenyl phenyl sulphides) were formed. However, diphenyl sulphone and nitrophenyl phenyl sulphoxide were not detected among the reaction products. 

Oxidative chlorination of diaryl sulphoxides with chlorine is generally much more useful than for alkyl-containing substrates. The sulphone is obtained cleanly, with no (or little) halogenation94 The rate of reaction is first-order with respect to both the sulphoxide and chlorine and has an order of minus one with respect to chloride ion. This is consistent with the mechanism given in equation (29). 

In aqueous pyridine solution, most diaryl sulphoxides may be oxidized to the corresponding sulphones with (dichloroiodo)benzene in reasonable yields103. The reaction involves nucleophilic attack by the sulphoxide on the electrophilic chlorine-containing species, yielding an intermediate chlorosulphonium ion which then reacts with water producing the sulphone. If the sulphoxide is optically active, then an optically active sulphone is produced in excellent optical yield when the reaction is carried out in oxygen-18 labelled water104, as indicated in equation (33). 

The anodic oxidation reaction of sulphoxides was not much studied, and just a few reports are available so far. The conversion into the corresponding sulphones of some phenyl alkyl and diaryl sulphoxides (oxidation potential for 86 + 2.07 V vs. SCE in acetonitrile/NaC104 electrolyte, Pt anode) has been reported. Similarly, diphenyl suiphoxide was long known to be transformed in a quantitative yield into the sulphone (Pt anode, solvent glacial acetic acid). Additional examples of the oxidation of a suiphoxide function attached to aryl groups are available . 

Geranyl phenyl sulphides or sulphones, Me2C=CHCH2CMe=CHCHXY (33 X = H Y = SPh or SOjPh), cyclized to cyclocitral derivatives under acid conditions, whereas the corresponding dithioacetal (33 X = Y = SPh) gives the thiochroman (34). The novel heterocycles (35) have been prepared by standard methods from the corresponding tellurochromanones. The critical step in the synthesis of the latter consists of reduction of the appropriate diaryl ditelluride with borohydride and subsequent reaction with 3-chloropropionic acid under carefully controlled conditions. 

---