Polyphenols deriving from chalcones: investigations of redox activities

The redox properties of a series of hydroxychalcones (a group of polyphenols abundantly present in plants) were investigated by cyclic voltammetry. As for many polyphenols, their beneficial properties have been mainly related to their antioxidant activities, which in turn are directly associated to their redox behavior. Two types of radicals can be produced that are localized on either one of the two aromatic systems. Their thermodynamic and kinetic parameters were extracted and compared to the predictions of density functional theory calculations. When at least one OH is present on each ring, their behaviors are dominated by the conjugated system: phenolic ring A-double bond-ketone, which is the only one to be oxidized. However, the redox properties of this conjugated system are strongly influenced by the presence of ring B. When an OH is present on ring B, an important feature is the existence of strong hydrogen bonding that remains almost unmodified even when ring A is oxidized. It does not considerably change the thermodynamics of ring A but strongly increases the rigidity of the molecule that remains planar under the neutral, anionic, or radical forms. Oxidation potentials of the phenolates range between 0.1 and 0.2 V versus a saturated calomel electrode, which correspond to species that are very easy to oxidize and lead to the rapid formation of nonradical species, underlining the potential antioxidant properties of these molecules.     

EPR of free radicals formed from 3-hydroxyesculetin and related derivatives

EPR spectroscopy of 3-hydroxyesculetin (1, solid and in solution) and of the radicals formed during the aerobic oxidation of alkaline solutions of 1 and related compounds was investigated. 1 in the solid state was studied by pulsed EPR experiments and showed a radical character. The aerobic oxidation of alkaline solutions of 1 was also followed by EPR spectroscopy. A ring contraction occurred leading to a 5,6-dihydroxybenzofuran-2-carboxylate radical. The autoxidation of an alkaline solution of (Z)-3-(3,4-dihydroxyphenyl)-2-hydroxypropenoic acid allowed the observation of a spectrum attributable to 5,6-dihydroxybenzofuran-3-one-2-carboxylate radical. The formation mechanisms of these radicals are discussed.     

Electrophilic Nitration of Electron-Rich Acetophenones

It is demonstrated that electron-rich disubstituted acetophenones react according to various electrophilic nitration conditions that generally lead to ipso substitution accompanying the conventional reaction. The hydroxy substituent does not seem prone to favor such behaviour.     

NMR evidence for an NH+ …OC intramolecular hydrogen bond in 2-alkyl-3-morpholinopropiophenones—structure of a new elevated high density lipoprotein agent in solution

7-[2-(4-morpholinomethyl)butanoyl]-4-methyl-2H-1, 4-benzoxazin-3 (4H)-one hydrochloride (2a) (a new elevated high density lipoproteins agent) and related compounds have been studied by NMR spectroscopy. Compound 2a exhibits an intramolecular hydrogen bond between the NH⁺ and CO bonds in solvents with low nucleophilicity. These results are confirmed by IR spectroscopy in solution.     

Electrophilic Nitration of Electron-Rich Acetophenones

Summary. It is demonstrated that electron-rich disubstituted acetophenones react according to various electrophilic nitration conditions that generally lead to ipso substitution accompanying the conventional reaction. The hydroxy substituent does not seem prone to favor such behaviour.     

Erratum

A new method of acylation of 2,3-dihydrobenzoxazol-2-one 1 is proposed in a two-steps procedure involving an acyl migration.     

Selective Synthesis of 2,5-Dimethoxy-4-nitrobenzaldehyde

A selective preparation of 2,5-dimethoxy-4-nitrobenzaldehyde is proposed in a procedure involving the transformation of the aldehyde group to a diacetoxymethyl group.     

Ceric Ammonium Nitrate in Organic Synthesis III. A Facile Synthesis of Methoxylated 3, 4 Dihydroisoquinolinium Nitrates

A mild and efficient method for the synthesis of 3, 4-dihydroisoquinolinium salts, key intermediates for the preparation of isoquinoline alkaloïds, by an oxidation of N-methyl-1, 2, 3, 4-tetrahydroisoquinolines using ceric ammonium nitrate (CAN) is described.     

Nitrodecarboxylation and Nitrodeformylation of Some Electron-Rich Benzoic Acids and Benzaldehydes

The nitration ipso to a carboxylic or formyl group of disubstituted and trisubstituted benzoic acids and benzaldehydes using nitric acid in acetic acid is described.