Olefination with Sulfonyl Halides and Esters: Synthesis of Unsaturated Sulfonyl Fluorides

[Image: see text] Methanedisulfonyl fluoride, CH(2)(SO(2)F)(2), transforms aromatic aldehydes into β-arylethenesulfonyl fluorides, useful substrates for the SuFEx “click”-type transformations. The reaction mimics mechanism of the Horner–Wadsworth–Emmons olefination, which runs via addition of the carbanion, followed by cyclization–fragmentation of the four-membered ring intermediate. In the absence of base, electron-rich aldehydes follow an alternative pathway of the Knoevenagel condensation to provide unsaturated 1,1-disulfonyl fluorides. We demonstrate also trapping of elusive ethene-1,1-disulfonyl fluoride, CH(2)=C(SO(2)F)(2), with 4-(dimethylamino)pyridine (DMAP) that forms zwitterionic adduct, characterized with X-ray studies.