Carbon-sulfur bond formation alkenes

Carbon-Sulfur Bond Formation. The oxidation of sulfl-nates by CAN provides an easy entry to sulfonyl radicals, which can be trapped by various alkenes, especially electron-rich ones, to afford sulfones. For example, the reaction of sodium 2-naphtha-lenesulflnate with 1-vinylcyclobutanol in the presence of CAN furnishes the ring-enlarged product (eq 27). With the aid of sodium iodide, the CAN-mediated oxidative addition of sulflnates to styrene affords vinyl sulfones and the addition to alkynes leads to /3-iodo vinyl sulfones. ... 

Decomposition of Thiols. Thiols decompose by two principal paths (i43— i45). These are the carbon—sulfur bond homolysis and the unimolecular decomposition to alkene and hydrogen sulfide. For methanethiol, the only available route is homolysis, as in reaction 29. For ethanethiol, the favored route is formation of ethylene and hydrogen sulfide via the unimolecular process, as in reaction 30. 

The formation of the carbon sulfur bond follows an anti-Markovnikov regios-electivity, which ensures the formation of the most stable carbon radical [42]. There are several reports establishing a general trend for the reaction of thiols with alkenes. Comprehensive reports in this regard were published by Hoyle et al. [43], where they compared the reaction of three families of thiols, namely alkyl-3-mercaptopropionates, alkyl thioglycolates, and alkyl thiols, with various alkenes. The reactivity order provided by them is as follows norbornene > vinyl ethers > propenyl > alkenes allyltriazines allyl isocyanurates > acrylates > N-substituted maleimides > acrylonitrile methacrylates > styrene > conjugated dienes. 

Thiirane 1,1-dioxides extrude sulfur dioxide readily (70S393) at temperatures usually in the range 50-100 °C, although some, such as c/s-2,3-diphenylthiirane 1,1-dioxide or 2-p-nitrophenylthiirane 1,1-dioxide, lose sulfur dioxide at room temperature. The extrusion is usually stereospeciflc (Scheme 10) and a concerted, non-linear chelotropic expulsion of sulfur dioxide or a singlet diradical mechanism in which loss of sulfur dioxide occurs faster than bond rotation may be involved. The latter mechanism is likely for episulfones with substituents which can stabilize the intermediate diradical. The Ramberg-Backlund reaction (B-77MI50600) in which a-halosulfones are converted to alkenes in the presence of base, involves formation of an episulfone from which sulfur dioxide is removed either thermally or by base (Scheme 11). A similar conversion of a,a -dihalosulfones to alkenes is effected by triphenylphosphine. Thermolysis of a-thiolactone (5) results in loss of carbon monoxide rather than sulfur (Scheme 12). 

There is no clear reason to prefer either of these mechanisms, since stereochemical and kinetic data are lacking. Solvent effects also give no suggestion about the problem. It is possible that the carbon-carbon bond is weakened by an increasing number of phenyl substituents, resulting in more carbon-carbon bond cleavage products, as is indeed found experimentally. All these reductive reactions of thiirane dioxides with metal hydrides are accompanied by the formation of the corresponding alkenes via the usual elimination of sulfur dioxide. 

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