2‐(Pyridinium‐1‐yl)‐1,1‐bis(perfluoroalkylsulfonyl)ethan‐1‐ide: A Practical Reagent for Synthesis of Strongly Acidic 1,1‐Bis(perfluoroalkylsulfonyl)alkanes

Abstract

On mixing (R SO ) CH (R =perfluoroalkyl), paraformaldehyde, and substituted pyridines, a three-component reaction proceeded smoothly to give unusual zwitterions bearing both pyridinium and stabilized carbanion moieties in good to excellent yields. Of these, 2-fluoropyridinium derivatives rapidly dissociated in acetonitrile to give equilibrium mixtures of the zwitterions and (R SO ) C=CH /2-fluoropyridine, as confirmed by detailed variable-temperature NMR studies. The dynamic behavior of such 2-fluoropyridinium compounds allows them to be used as shelf-stable, easy-to-handle sources of (R SO ) C=CH . With these reagents, strongly acidic carbon acids (R SO ) CHR were synthesized, which served as a new type of acid catalysts. Moreover, C-C bond-forming reactions with a ketene silyl acetal proceeded efficiently with Tf C=CH generated in situ.

Regioselective Synthesis of Heteroatom‐Functionalized Cyclobutene‐triflones and Cyclobutenones

“…As shown in Scheme 9, the mechanism for the cyclobutenone formation involves two main processes, namely, cyclobutene ring construction and hydrolysis. The proposal for the first process (formation of 11mt) is based on our previous DFT studies of 1-aryl-2alkyl-4,4-bis(triflyl)cyclobutenes, [5] but now the regioselectivity is dictated by the electronic effects of the heterocyclic amine. Adventitious water in the reaction medium is required for the double trifluoro(hydrosulfonyl)methane (TfH) elimination, giving rise to hydrates 17.…”

“…These heteroatom-substituted cyclobutenetriflones. [4], [5] should bring together the new properties conferred by heteroatoms and trifyl group with the exceptionally rich chemistry of cyclobutenes.…”

p<i>K</i>_a Determination of Strongly Acidic C-H Acids Bearing a (Perfluoroalkyl)sulfonyl Group in Acetonitrile by Means of Voltammetric Reduction of Quinone

“…(RfSO 2 ) 2 CHR and the related C-H acids were prepared according to a previous report. 5 Voltammetry was conducted with an electrochemical analyzer (HZ-7000, Hokuto Denko,…”

“…4 Against such a background, Yanai and coworkers successfully developed an effective method for the incorporation of the (RfSO 2 ) 2 CH group (Rf = perfluoroalkyl) into several nucleophilic compounds. 5 The C-H (carbon) acids thus obtained have found applications as Brønsted acid catalysts for organic reactions. 6 Lithium salts derived from the acids have also been utilized as electrolytes or additives to lithium-ion secondary batteries.…”

Synthesis and Characterization of Stable Phosphorus Carbabetaines

“…[11] Recently,w efound that 2-fluoropyridinium salt 3 was an effective reagent for the in situ generation of highly electrophilic1 ,1-bis(trifluoromethylsulfonyl)ethylene (4;S cheme1)a nd was successfully appliedt ot he synthesis of as uperacidic carbon acid, denoteda sT f 2 CHR. [12] Cycloaddition reactions of in-situ-generated compound 4 with 1,3-dienes, [12b, 13] alkynes, [14] and organica zides [15] also proceeded smoothly to produce the corresponding triflones. Although 2-fluoropyridinium salt 3 rapidly formed an equilibrium mixture of compound 4 and 2-fluoropyridine in MeCN, the reagent itself is as helf-stable and easy-to-handle crystalline solid.…”