Substituents sulfur-containing groups

In aromatic sulfones, sulfonamides, and sulfoxides with electron-donating substituents in the ortho, meta, and para position, the sulfur-containing group was displaced by a cyano group on irradiation in a t-BuOH/aqueous solution of KCN (see Scheme 4.19). The yields of photosubstitution products deaeased on passing from aryl sulfones to aryl sulfoxides and followed the order para > ortho > meta. [118-120] Analogously, when dichloroanilines were used as the substrates, the corresponding dicyano derivatives were obtained [120]. 

Olefin synthesis starts usually from carbonyl compounds and carbanions with relatively electropositive, redox-active substituents mostly containing phosphorus, sulfur, or silicon. The carbanions add to the carbonyl group and the oxy anion attacks the oxidizable atom Y in-tramolecularly. The oxide Y—O" is then eliminated and a new C—C bond is formed. Such reactions take place because the formation of a Y—0 bond is thermodynamically favored and because Y is able to expand its coordination sphere and to raise its oxidation number. 

Contrary to the expectation that a sulfur-containing substituent will be a catalyst poison, a phenylthio group serves as an effective selectivity control element in TMM cycloadditions. A single regioisomer (30) was obtained from the carbonate precursor (31) in good yield. The thermodynamically more stable sulfide (32) is readily accessible from (30) via a 1,3-sulfide shift catalyzed by PhSSPh. A wide array of synthetically useful intermediates could be prepared from the sulfides (30) and (32) with simple transformations (Scheme 2.10) [20]. 

The effect of sulfur-containing substituents on free radicals appears to be a topic of current interest, so we will discuss it briefly insofar as it concerns sulfinyl and sulfonyl groups. Our discussion will refer mainly to a few recent papers, which usually contain copious references to earlier work see also Block247. 

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