Nature of sulfonyl deactivation/activation by metal catalysts†

Molecule activation theories are important in catalytic reactions, but sulfonyl activation remains unclear despite the fact that sulfonyl is a widely used leaving group in chemical synthesis. To unveil the nature of sulfonyl deactivation/activation by metal catalysts, the mechanisms of the competitive metal-catalyzed α-alkylation of sulfones and sulfonyl dissociation (Julia olefination) reactions are comprehensively investigated. A favorable metal-catalyzed mechanism is first proposed for the sulfonyl dissociation reaction. The sulfonyl dissociation and chemoselectivity are revealed to originate from hydride addition into the CC bond of the vinyl sulfone intermediate. Through natural localized molecular orbital analysis, a sulfonyl deactivation model with a π_C(α)C(β) → σ*_S–O hyperconjugation effect and a sulfonyl activation model with π_C(α)C(β) → π*_Ph conjugation effect are proposed. Guided by the sulfonyl activation model, switchable chemoselectivity strategies are provided to control these reactions.