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

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