Background: Ketenium ions are rarely used in chemical synthesis, despite a strong potential
and their high reactivity, which can be mostly attributed to their difficult generation. There is
therefore an important need for efficient methods enabling their in situ generation from stable and
readily available starting materials in order to fully exploit the unique reactivity of ketenium ions.
Method: We report in this manuscript a simple and efficient process for the generation of these highly
reactive intermediates by simple protonation of the corresponding stable and readily available aryl
ynol ethers with bistriflimide. By simply mixing these two reagents in dichloromethane at -50°C for
30 minutes, a transient ketenium ion is formed and is further, quite unexpectedly, trapped by the
poorly nucleophilic bistriflimidate.
Results: The scope of the reaction was delineated by using various aryl ynol ethers which were shown
to be excellent precursors of ketenium ions. Their trapping with bistriflimidate further highlights the
exceptional electrophilicity of these unique intermediates.
Conclusion: We have demonstrated that ketenium ions can be conveniently prepared by simple protonation
of the corresponding aryl ynol ethers, bench-stable and readily available starting materials. The
unique electrophilicity of these cationic heterocumulenes was showcased by their trapping with poor
nucleophiles such as bistriflimidate and in an intramolecular Friedel-Crafts reaction.