Generation and NMR Study of Short-Lived and Reactive Trifluoroalkyl Carbocations of the α-Halogenothiophene Series in Brønsted Superacids: Reactions of the Cations with Arenes.

Protonation of oxygen in the side chain of the MeSiO group (followed by the elimination of MeSiOH) and protonation of the thiophene ring in 2-chloro(or bromo)-5-(1'-MeSiO-1'-trifluoromethyl-alkyl)thiophenes in Brønsted superacids (CFSOH, FSOH) gave rise to short-lived and reactive trifluoroalkyl carbocations of the thiophene series. These cations were studied by low-temperature NMR spectroscopy in the superacids, which shed light on their reactivity and reaction mechanisms. The cations may react with (hetero)aromatic π-nucleophiles in various directions, depending on their structures as well as the reaction temperature and time. These transformations resulted in the formation of novel fluoro-organics of the thiophene family, namely, products of arylation of both the thiophene system and its side chain, hydrodehalogenation of halothiophenes, or electrophilic "dimerization".