Sulfinate anions, oxidation

Finally, it is worth noting that the generation of sulfonyl radicals through the oxidation of sulfinate anions has allowed these tandem reactions to be extended to cyclizations onto aromatics which need an oxidative termination [50] (Eq. 20). 

An example of fluoride induced conversion is of a hetaryl 2-(trimethylsilyl)ethyl sulfone to the sulfinic acid via protonation of the sulfinate anion. The treatment of a collection of arenesulfinate anions, obtained from the corresponding 2-(trimethylsilyl)ethyl sulfones, with H2NOSO3H gave aryl sulfonamides in 50-85% yield (eq 13). In this case and elsewhere, the aryl 2-(trimethylsilyl)ethyl sulfones are prepared through the deprotonation of aryl methyl sulfones and quenching of the a-sulfonyl carbanion with trimethylsilylmethyl iodide, or the less expensive trimethylsilylmethyl chloride. Such a protocol is complementary to the oxidation of 2-(trimethylsilyl)ethyl thioethers. 

Organolithiums have been shown to add to a variety of trithiocarbonate oxides exclusively in a thiophilic maimer, as a consequence of the electrophilic character of the sulfine sulfur, to give an intermediate carbanion stabilized by three sulfur atoms the soft carbanion, which forms trithioorthoester oxide on quenching with water, acts as the equivalent of the (alkylthio)carbonyl anion in Michael addition.98... 

Resin-bound 7-keto sulfones, prepared in a straightforward, three-step process comprising alkylation of a resin-bound sulfinate salt, alkylation of a sulfone-supported anion with an epoxide, and Jones oxidation of the 7-hydroxy sulfone, provided a source of structurally diverse three-carbon fragments <2004JC0928>. Reaction with a phenylenediamine to give the 1,5-benzodiazepine presumably occurs via initial imine formation followed by expulsion of the resin-bound sulfone, which acts as a traceless linker (Scheme 73). Yields for this process are a modest 10-38%. 

Thiols are susceptible to oxidation by peroxides, molecular oxygen, and other oxidizing processes (e.g., radical-catalyzed oxidation) (Fig. 67). Because thiols easily complex with transition metals, it is believed that most thiol autoxidation reactions are metal-catalyzed (108). Autoxidation of thiols is enhanced by deprotonation of the thiol to the thiolate anion. Thiol oxidation commonly leads to disulfides, although further autoxidation to the sulfinic and, ultimately, sulfonic acid can be accomplished under basic conditions. Disulfides can be reduced back to the thiol (e.g., upon addition of a reducing agent such as dithiothreitol). Thiols are nucleophilic and will readily react with available electrophilic sites. For a more thorough discussion, see Hovorka and Schoneich (108) and Luo et al. (200). 

The kinetics of the oxidation of l-phenyl-2-thiourea by chlorite, in aqueous acidic media, are strongly influenced by the pH and show a complex acid dependence. The proposed mechanism involves HOC1 as a major intermediate whose autocatalytic production determines the observed kinetics of the reaction. The oxidation involved the formation of two stable intermediates, the sulfinic acid and the sulfonic acid, on the pathway towards total desulfurization to form phenylurea. A comprehensive 29-reaction scheme has been proposed to describe the observed complex kinetics.96 The oxidation of trimethylthiourea (TMTU) by chlorite in slightly acidic media is very fast. The oxidation of TMTU proceeds through the formation of sulfinic acid then to the sulfoxylate anion. The direct reaction of chlorine dioxide and TMTU is autocatalytic and is also inhibited by acid. A series of 28 reactions have been proposed to describe the mechanism.97... 

Little woik has been earned out on sulfinylation reactions on those systems having thiocarbonyl and imino moieties. However, hydrazones are converted to a-sulfmyl derivatives on reaction of their anions (prepared from LDA in THF) at -78 C with sulfinate esters, although the full utility of this reaction remains to be explored. Furthermore, in an unusual reaction, p-toluenesulfinyl chloride has been shown to effect a facile one-step dehydrogenation of the thiolactam (17 equation 7) in good yield. These reactions contrast with the oxidative removal of thiocarbonyl, hydrazonyl and similar functionalities with Se species (see Section 2.2.4.2). 

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. 

Finally mixing of aliphatic or aromatic nitroso compounds with benzene sulfinic acid leads immediately to formation of benzene-sulfonylaminyloxides75. Aminyl-oxide anion 62 was detected when nitrosobenzene was allowed to react with aqueous hydrogensulfite in presence of lead dioxide76. With nitroso trifluoromethane radical 63 was formed. With tetraphenylarsonium cation this radical anion even formed a solid, paramagnetic precipitate77. ... 

Other methods, among which thermolysis or photolysis of tetrazene [59], photolysis of nitrosoamines in acidic solution [60], photolysis of nitrosoamides in neutral medium [61], anodic oxidation of lithium amides [62], tributylstannane-mediated homolysis of O-benzoyl hydroxamic derivatives [63, 64], and spontaneous homolysis of a transient hydroxamic acid sulfinate ester [65] could have specific advantages. The redox reaction of hydroxylamine with titanium trichloride in aqueous acidic solution results in the formation of the simplest protonated aminyl radical [66] similarly, oxaziridines react with various metals, notably iron and copper, to generate a nitrogen-centered radical/oxygen-centered anion pair [67, 68]. The development of thiocarbazone derivatives by Zard [5, 69] has provided complementary useful method able to sustain, under favorable conditions, a chain reaction where stannyl radicals act simply as initiators and allow transfer of a sulfur-containing... 

Dialkyl arenesulfinylmethanephosphonates are available by S-oxidation of the corresponding dialkyl arenesulfenylmethanephosphonates or by reaction of anions derived from dialkyl methanephosphonates with sulfinate esters. With regard to the synthesis of optically active a,P-unsaturated sulfoxides, the former method may not be applied in the absence of a reliable, highly enantioselective 5-oxidation procedure without recourse to resolution methods, while the latter method suffers from the relatively polar nature of dialkyl arenesulfinylmethanephosphonates, which renders their chromatographic separation tedious and costly. 

The oxidation of tetrametliylthiourea (TTTU) by bromine and acidic bromate ion in aqueous media has been studied. The bromate reaction, which has an induction period followed by formation of bromine, involves formation of tetramethythiourea sulfenic acid, which is oxidized to tetramethylurea and sulfate ion as final products. There was no evidence for formation of the sulfinic and sulfonic acids, which implicated the sulfoxylate anion as a precursor to formation of sulfate ion. ... 

---