Sulfinate ion

In reactions at the sulfur atom of a sulfinate ion to form a sulfone, of a sulfoxide to form R3S+—0, or of bisulfite ion to form a sulfonic acid, the fractionally positive sulfur becomes more positively charged in the poly-ionic transition states. Definitive experimental evidence... 

Tamttra and coworkers have reported a related sttbsdntdon reacdon cyclic ct-fnitroalkyl enones undergo regioselecdve sttbsdnttion of the nitro group by sulfinate ion, amino, and carbon nucleophiles fEq. 7.23. Several reacdon pathways are envisioned for this useful... 

Phenanthro[4,5-b, c, d]thiophene 4-oxide (19) and 4,4-dioxide (20)15 undergo first the well-known sulfenate (22) or sulfinate ester (23) rearrangements1 4,6, respectively (equation 6). The sulfoxide loses an oxygen atom and enters the fragmentation pathway of 18 or loses HCO (more likely in two steps) from 22. Both sulfenate and sulfinate ions can fragment further via 21 after losing a sulfur atom or eliminating SO5, respectively. 

Under certain basic conditions 2,5-dihydrothiophene 1,1-dioxides undergo ring opening reactions108,109 and the resulting buta-l,3-dienyl sulfinate ions may be alkylated... 

Watt and coworkers139 prepared the a-azidoaldehydes (242) by nucleophilic ring opening with sulfinate ion expulsion of a, /(-epoxy sulfones 241 with sodium azide in DMF... 

Reaction between aryl halides and sulfinate ions... 

Nucleophilic substitution reactions of sulfinate ions 106 Addition of sulfinate ions to multiple bonds 108 Radical reactions of sulfinic acids 110... 

Desulfonylation (loss of sulfur dioxide) occurs with particular ease for those sulfinic acids RS02H where the carbanion R generated by loss of sulfur dioxide from RSOj is stabilized (Kharasch et al., 1955 Haszeldine and Kidd, 1955). Other examples of desulfonylation are noted by Stirling (1971). King and Beatson (1970) have shown that the sulfinate ion of an a-halosulfinic acid can decompose in a rather different way (120), yielding a sulfene. 

By far the commonest and most extensively studied reactions of sulfinate ions are those in which they act as a nucleophile, either to perform a substitution, or to undergo addition to activated carbon-carbon multiple bonds or carbonyl groups. The detailed literature on the many examples of such reactions has been well reviewed by both Stirling (1971) and Oae (1977). We will attempt here only to summarize some of the conclusions of mechanistic interest. 

The carbonyl group of an acid chloride is also a sufficiently electropositive center that acylation of a sulfinate ion occurs at oxygen (123) rather than sulfur (Schank, 1967 Kobayashi, 1966b). The mixed sulfinic-carboxylic anhydrides... 

With sulfinyl chlorides the isolated product of their reaction with sulfinate ions is the sulfinyl sulfone (126) (Bredereck et al., 1960). However, whether this results because S-sulfinylation is kinetically preferred, or rather comes about because the sulfinic anhydride resulting from initial O-sulfinylation is readily converted by some of the remaining sulfinate ion to the thermodynamically more stable sulfinyl sulfone (126a), does not appear to have ever been definitely established. 

Addition of sulfinate ions to the carbonyl group of aldehydes to form c-hydroxy sulfones (Bredereck et al., 1954, Bredereck and Bader, 1954) is also known, as is the participation of sulfinic acids as the acid component in Mannich-type condensation reactions with aldehydes (129) (Rawson and Engberts, 1970 Engberts and Strating, 1964, 1965). 

Addition of arenesulfinates to N,N-dialkyl-p-quinodi-imines (130) is an interesting reaction in that it yields products from addition of the sulfinate ion to both carbon and nitrogen, with the product ratio varying markedly with pH (Finley et al., 1969). The reason for the variation with pH is that the initial addition to carbon (but not the one to nitrogen) is reversible. To get a... 

In all of these additions to various types of multiple bonds one notes that only products containing a sulfonyl group are obtained. There is never any indication of a bond being formed between a sulfinate oxygen and the species to which the addition is occurring. The same is apparently also true in the addition of a sulfinate ion to a sulfine (Veenstra and Zwanenburg, 1976). There addition occurs to the sulfur atom of the sulfine to form a sulfinyl sulfone ... 

A wide variety of other common nucleophiles also displaces sulfinate ion from a sulfinyl sulfone (139) very readily (Kice and Mullan, 1976). With these... 

Although not as good a leaving group as a sulfonate (ArSOj) or a halide ion (X ), a sulfinate ion (ArSOj) is still sufficiently good that it can be displaced from sulfenyl sulfur by a wide variety of nucleophiles. As a result the chemistry of thiolsulfonates is dominated by reactions of the general type shown in (167). 

Scheme 2.1.4.2 Pd-catalyzed enantioselective allylic alkylation of a sulfinate ion and kinetic resolution of a racemic allylic ester.

The bisphosphane BPA was selected as a ligand for the Pd atom because of the high enantioselectivities which had been recorded in the allylation of sulfinate ions with racemic allylic carbonates (vide supra). Besides the variations of the carbon skeleton, the substituent on the S atom of the racemic allylic sulfinates was varied in order to see whether both aryl and alkyl sulfinates are amenable to a highly selective rearrangement. 

The Pd-catalyzed allylic alkylation of sulfinate ions, thiols, and thiocarboxylate ions with racemic cyclic and acyclic allylic esters in the presence of bisphosphane BPA generally provides for an efficient asymmetric synthesis of allylic sulfones, sulfides, and thioesters. The Pd-catalyzed rearrangements of allylic sulfinates and allylic O-thiocarbamates, both of which proceed very efficiently in the presence of BPA, are attractive alternative ways to the asymmetric synthesis of allylic sulfones and allyUc thioesters also starting from the corresponding racemic alcohols. 

Rearrangements which take place in carbocation sulfinate ion pairs, C+ArSC>2, may involve re-bonding to the same sulfinate oxygen or bonding to the other one, according to labelling studies.147 The processes studied included the norbornynorbomyl and... 

The photosensitive system used by the Hughes group is based on a dye, such as methylene blue, and toluenesulfinic acid. The dye is excited by helium-neon laser light (632.8 nm) and it is then reduced by sulfinate ion to form a radical known to initiate acrylate polymerization ... 

In the years to follow this chemistry was developed further and it turned out that especially the Pd(0)-catalyzed alkylation of sulfinate ions with racemic allylic carbonates provides an excellent means for the asymmetric synthesis of allylic sulfones [52-55]. Despite these successes the efforts to use 2-alkenylsulfinates as precursors for enantioenriched allylic sulfones never stopped [56]. 

Reductive cleavage of 6-ketosulfones [166], RC0CHR S02R", in DMF at mercury is a practical way of preparing alkyl ketones the primarily formed radical anion cleaved to a radical RCOCHR and a sulfinate ion R"S02. Since the anodic reaction was the oxidation of R"S02" to R"S03, an undivided cell could be used. 

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