The cheletrofic fragmentation of hypervalent three-membered thiahetesocyclic intermediates

Lithio-imidazolium salts 10, generated in-situ from N,N-dimethylimidazolium salts 9, readily undergo sulfonylation with sulfur dioxide, sulfines, N-sulfinylamines, and thiirane. The resulting zwitterionic species 4 fragment thermally to yield the corresponding imidzaolium thione 5 with the hypervalent three-membered thiaheterocyclic intermediates 3 connecting 4 and 5 on the reaction surface. The non-linear cheletropic fragmentation of these relatively stable hypervalent sulfuranes appears to be general for this class of compounds (3 or 4), and the experimental results are in accord with theoretical considerations.