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

Methanedisulfonyl fluoride, CH₂(SO₂F)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, CH₂═C(SO₂F)₂, with 4-(dimethylamino)pyridine (DMAP) that forms zwitterionic adduct, characterized with X-ray studies.