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 TfC=CH (Tf=CFSO), 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.

HFIP-Mediated Desulfinative Friedel-Crafts Cyclobutenylation Reaction.

In 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP), gem-bis(triflyl)cyclobutenes, which can be prepared by the (2+2) cycloaddition reaction of TfC=CH with alkynes, underwent desulfination to generate the corresponding cyclobutenyl cation. This unique reactivity was successfully applied to the Friedel-Crafts type cyclobutenylation reaction of several (hetero)aromatic compounds.

Synthesis of Spirocyclic Cyclobutenes through Desulfinative Spirocyclisation of gem-Bis(triflyl)cyclobutenes.

A two-step synthesis of less accessible spiro[cyclobutene-1,9'-fluorene] compounds from biaryl-alkynes and 2-(2-fluoropyridin-1-ium-1-yl)-1,1-bis((trifluoromethyl)sulfonyl)ethan-1-ide, which serves as a potent precursor for outstandingly electrophilic Tf C=CH , has been developed. This synthetic methodology includes selective formation of gem-bis(triflyl)cyclobutenes from biaryl-alkynes and Tf C=CH followed by desulfinative spirocyclisation mediated by 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP). Besides, on the basis of the chameleonic reactivity of sulfone functionality, several derivatisations of triflylated spiro[cyclobutene-1,9'-fluorene] products have been successfully achieved.

Synthesis of Polycyclic Aromatic Hydrocarbons Decorated by Fluorinated Carbon Acids/Carbanions.

The carboarylation reaction of biphenyl-alkynes was successfully triggered by electrophilic attack of 1,1-bis(triflyl)ethylene on the alkyne moiety to give polycyclic aromatic hydrocarbons (PAHs) decorated by superacidic carbon acid functionality. Neutralisation of thus obtained acids with NaHCO yielded the corresponding sodium salts, which showed improved solubility in both aqueous and organic solvents.

A catalyst-free bis(triflyl)ethylation/benzannulation reaction: rapid access to carbazole-based superacidic carbon acids from alkynols.

Carbazoles possessing TfCHCH groups were obtained by the reaction of 1-(indol-2-yl)but-3-yn-1-ols with in situ-generated TfC[double bond, length as m-dash]CH through vicinal difunctionalisation of the alkyne moiety, where the vinyl-type carbocation intermediate was selectively attacked by the indole moiety and not by the carbanion moiety.