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A simple, inexpensive, and mild one-pot methodology for the synthesis of novel 4-aryl-3-methyl-1,2,3,4-tetrahydroquinolines derivatives using aqueous HCl as catalyst has been developed. The key step involves the formal inverse-electron-demand [4π+ + 2π] cycloaddition reaction of in situ–generated cationic 2-azadienes with arylpropenes (isoeugenol and trans-anethole). Iminium ion intermediates are generated through the condensation between N-benzylanilines and formalin. The products are obtained with good to excellent yields and high trans-diastereoselectivity. Further catalytic hydrogenation (Pd/C) allowed debenzylation to successfully obtain the respective 4-aryl-3-methyl-N-H-tetrahydroquinolines of interest. Recent reports suggest that these compounds could serve as interesting models in pharmacological studies against parasites that cause the most common tropical diseases.

A simple and efficient one-pot method for the synthesis of new 2,4-diaryl-1,2,3,4-tetrahydroquinolines using a three-component imino Diels–Alder cycloaddition between trans-isoeugenol or trans-anethole, anilines, and benzaldehyde in the presence of BF3·OEt2 in PEG-400, a green and reusable solvent, has been developed. Also, BF3·OEt2-catalyzed formal [3+2] cycloaddition reaction of trans-isoeugenol or trans-anethole with 1,4-benzoquinone in PEG-400 to give dihydrobenzo[b]furan derivatives has been described.

A simple and efficient one-pot method for the synthesis of 4-anisyl-2-phenyl-1,2,3,4-tetrahydroquinoline derivatives using a three-component imino Diels–Alder cycloaddition (Povarov reaction) between anilines, benzaldehyde, and trans -anethole in the presence of acidic catalysts is shown. New substituted tetrahydroquinolines are reported and their direct preparation from the anise essential oil is described. Also, a simple procedure of the same tetrahydroquinolines from the anise seeds under supercritical fluid (CO 2 ) conditions has been reported.

New effective approach to the synthesis of a wide variety of C-2 nitro or aminophenyl substituted quinolines was reported using diverse intermediate 4-(2-oxopyrrolinidyl-1)-tetrahydroquinolines that were prepared by a three component imino Diels-Alder reaction was reported. The key aromatisation process occurs cleanly with the loss of the 2-oxopyrrolinidyl-1 fragment.