Intermediates, fluorinated sulfur anions

Fluorinated sulflnates are prepared from sodium dithionite and liquid per-fluoroalkyl halides [74] (equation 67). For the transformation of the gaseous and poorly reactive trifluoromethyl bromide, it is necessary to use moderate pressure [75] (equation 68) These reactions are interpreted by a SET between the intermediate sulfur dioxide radical anion and the halide The sodium trifluorometh-anesulfinate thus obtained is an intermediate for a chemical synthesis of triflic acid. 

IZV2066). This is probably associated with the fact that during the attack of the S-nucleophile the anion is mainly stabilized by elimination of the vinyl fluorine atom, since the intermediate anion formed in this process is energetically preferable to the isomeric anion due to conjugation between the lone electron pair of the sulfur atom and the double bond. The product is of interest in syntheses of pharmaceuticals and agrochemicals. 

Evidence against an ionic mechanism in such reactions is the observation that at 120°C, where reaction is slow, no acceleration was noted with added triethylamine. Evidence for a free radical mechanism is found in response to the presence of an olefin as a third reactant. Hydrocarbon olefins with one substituent intercept intermediate 1 more eflBciently than does tetrafluoroethylene, and they give partially fluorinated thiolanes of type 4. Regardless of the electronegativity of the olefinic substituent, yields are good (40-60% ), and products have the substituent on a carbon adjacent to sulfur in the ring (4). An intermediate of the type 5, in which nearly any substituent provides some stabilization to the adjacent radical center, is implicated. Cationic or anionic intermediates result in pronounced deviations from the results observed. 

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