Synthesis and characterization of crowned 1,4-benzoquinones as ionophore-dienophile (redox) combined systems: double interaction with catecholamines and tryptamine

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Abstract
The crowned 1,4-benzoquinones (1)(15-crown-5) and (2)(18-crown-6) have been synthesized from pyrogallol (3) by: (1) the selective monobenzylation (4); (2) crown ether formation using a pyrocatechols (5) and (6); (3) debenzylation (7) and (8); and (4) oxidation to 1,4-benzoquinones. Both compounds (1) and (2) underwent smooth Diels–Alder reactions with cyclopentadiene (25 °C), thebaine (80 °C), and buta-1,3-diene (BF3·Et2O, 0 °C). The cyclopentadiene adducts (11) and (12) were photochemically transformed into the cage compounds (13) and (14), while the thebaine adducts (15) and (16) were smoothly converted into the hydroquinone derivatives (17) and (18) by silicic acid. The butadiene adducts (19) and (20) were transformed into the crowned naphthoquinones (23) and (24) in high yields. The redox potentials of these crowned quinones in the presence of alkali-metal ions were studied by cyclic voltammetry. The specific interaction between compound (2) and tryptamine, dopamine, and homoveratrylamine via ion-binding and charge-transfer complex formation was evidenced by u.v. spectroscopic studies.