TFA-mediated tandem Friedel-Crafts alkylation/cyclization/hydrogen transfer process for the synthesis of flavylium compounds.

The tandem reaction of phenols and chalcones in refluxing TFA gave the flavylium species of 2-hydroxy-2-phenyl-2H-chromenes in moderate to good isolated yields. The reaction was proposed to involve a tandem transformation of Friedel-Crafts alkylation, dehydrative cyclization, intermolecular hydrogen transfer, and hydration. As a multifunctional catalyst, TFA mediated the processes efficiently and cleanly.