Recyclable 2-Fluoropyridine Derivative as a Storage for Highly Electrophilic 1,1-Bis(triflyl)ethylene.

As an easy-to-handle reagent for the in situ generation of outstandingly electrophilic Tf₂C=CH₂ (Tf=CF₃SO₂), we have designed and synthesised a novel 4-substituted 2-fluoropyridinium zwitterion, in which a partially fluorinated alkyl group is attached to the pyridinium 4-position. Its zwitterionic nature has been well characterised by quantum chemical bonding analysis. By using this reagent, a wide variety of organic compounds, including commercial bioactive agents, were successfully decorated by the strongly acidic or ionic functionality. Remarkably, the 4-substituted 2-fluoropyridine derivative, which results from the zwitterion with the generation of Tf₂C=CH₂, can be rapidly separated and recovered from the reaction mixture appropriately using distillation, organic solvent extraction, or fluorous solid phase extraction techniques. Such multi-optionality for the purification methods favours in the isolation of the strongly acidic and/or ionic products.