Reactions of 3-(furan-2-yl)propenoic acids and their esters with arenes in Brønsted superacid TfOH affords products of hydroarylation of the carbon–carbon double bond, 3-aryl-3-(furan-2-yl)propenoic acid derivatives. According to NMR and DFT studies, the corresponding O,C-diprotonated forms of the starting furan acids and esters should be reactive electrophilic species in these transformations. Starting compounds and their hydroarylation products, at a concentration of 64 µg/mL, demonstrate good antimicrobial activity against yeast-like fungi Candida albicans. Apart from that, these compounds suppress Escherichia coli and Staphylococcus aureus.

Furan-2-yl substituted ethenes and conjugated butadienes containing two geminal electron-withdrawing groups, as well as phenylbutadienes with two electron acceptors, were synthesized from the corresponding aldehydes and various β-dicarbonyl compounds via aldol condensation. Reactions of these ethenylfurans and methyl 3-(benzofuran-2-yl)propenoate with arenes in triflic acid (TfOH) yield arylated 2,3-dihydrofurans and 2,3-dihydrobenzofurans, representing a novel synthetic approach to these dihydro derivatives. In contrast, analogous reactions of furanyl- and phenylbutadienes result in carbon–carbon bond cleavage through retro-aldol and related acid-promoted processes. We propose plausible multistep mechanisms and cationic intermediates for these transformations. The synthesized furans and related compounds, at a concentration of 64 μg/mL, exhibit moderate antimicrobial activity against the yeast-like fungus Candida albicans.