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Elimination Reactions of Alkanesulfinyl Derivatives: Mechanism and Reactivity in Base-Induced Sulfine Formation from Methyl Diarylmethanesulfinates
Kice, John L.,Rudzinski, Juliusz J.
, p. 2414 - 2421 (2007/10/02)
Upon treatment in methanol at room temperature with methoxide ion methyl diarylmethanesulfinates, ArAr'CHS(O)OCH3 (1), and methyl 9-fluorenesulfinate (2) undergo elimination readily to afford the corresponding sulfines (3 and 4) in quantitative yield.Studies in CD3O-/CD3OD show that, surprisingly, elimination of 1 to give 3 is significantly faster than nucleophilic substitution by methoxide ion at the sulfinyl group (exchange of CH3O by CD3O).Even more unexpected, the kinetic isotope effect for elimination of 2-9-d (kH/kD=6.1) and absence of detectable H/D exchange of the methine proton of 1 in CD3OD prior to sulfine formation extablish that, even though the leaving group is MeO-, the elimination takes place by either an irreversible ElcB or an E2 mechanism, rather than the reversible ElcB mechanism found (ref 4 and 7) for the analogous sulfene-forming elimination of arylmethanesulfonate esters with oxyanion leaving groups of comparable pKa.Reaction of amines with 2 in methanol also gives sulfine 4, and the amine-induced elimination, which has a large Broensted β, also proceeds by either an (ElcB)irrev or an ElcB-like E2 mechanism.Why sulfine-forming eliminations of 1 and 2 favor an (ElcB)irrev or E2 mechanism whereas sulfene-forming eliminations of arylmethanesulfonates with even better leaving groups proceed by an (ElcB)rev mechanism is considered and a possible explanation presented.
