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

摘要

Protonation of oxygen in the side chain of the Me3SiO group (followed by the elimination of Me3SiOH) and protonation of the thiophene ring in 2-chloro(or bromo)-S-(1'-Me3SiO-1'-trifluoromethyl-alkyl)thiophenes in Bronsted superacids (CF3SO3H, FSO3H) 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 pi-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".