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The reaction of 5‐hydroxy‐1‐pyrrolines with arenes in TfOH at room temperature for 1 h afford 5‐aryl‐1‐pyrrolines in 55–98 % yields. 5‐Hydroxy‐1‐pyrrolines in TfOH or H2SO4 at room temperature for 0.5–1 h undergo dehydration with the formation of N‐protonated forms of 3H‐pyrroles, which were characterized by NMR. Upon hydrolysis, the N‐protonated species give quantitatively the corresponding 3H‐pyrroles. The intermediate cationic species derived from the protonation of 5‐hydroxy‐1‐pyrrolines in Brønsted acids have been studied by means of NMR and DFT calculations. Plausible reaction mechanisms are discussed.

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.

Die Reaktion der Rhodanine (I) mit Formaldehyd (III) und den Alkylaminen (II) in Äthanol bei 0°C liefert die Mannich‐Basen (IV) (Ausbeute 75 bis 91%).