Elimination Reactions of Alkanesulfinyl Derivatives: Mechanism and Reactivity in Base-Induced Sulfine Formation from Methyl Diarylmethanesulfinates

Article abstract of DOI:10.1021/ja00242a027

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 (k_H/k_D=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 pK_a.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.