Superacid-promoted reactions of pyrazolecarboxaldehydes and the role of dicationic electrophiles

Pyrazolecarboxaldehydes react in the Brønsted superacid triflic acid (CF3SO3H, TfOH) to generate electrophilic intermediates capable of reacting with benzene in condensation reactions. Appropriately substituted pyrazoles may also undergo intramolecular Friedel–Crafts-type reactions. It is proposed that the pyrazolecarboxaldehydes and related systems form diprotonated intermediates in these reactions.