General method for the high yield preparation of 2-(4-X-phenylene)amine-1,4-naphthoquinones (X=ferrocenyl, OMe, Me, I, Cl, and NO2) from 2-methoxy-1,4-naphthoquinone and investigation of H+ and Mg2+ catalysts with DFT calculations

Blue Light Irradiated Metal-, Oxidant-, and Base-Free Cross-Dehydrogenative Coupling of C(sp2)-H and N-H Bonds: Amination of Naphthoquinones with Amines

Herein, we report a blue-light-driven amination of C(sp²)-H bond of naphthoquinones and quinones with the N-H bond of primary and secondary amines for the synthesis of 2-amino-naphthoquinones and 2-amino-quinones. The coupling of naphthoquinones with a wide array of aliphatic, aromatic, chiral, primary, and secondary amines having electron donating (-CH₃, -OCH₃, -SCH₃), withdrawing (-F, -Cl, -Br, -I), and CO₂H, -OH, -NH₂ groups with acidic protons selectively occurred to afford C-N coupled 2-amino-naphthoquinones in 60-99% yields and hydrogen gas as a byproduct in methanol solvent without using any additional reagents, additives, and oxidant under the blue light irradiation. Mechanistic insight by DFT computation, controlled experiments, kinetic isotopic effect, and substitution effect of the substrates suggest that the reaction proceeds by radical pathway in which naphthoquinone forms a highly oxidizing naphthoquinonyl biradical upon irradiation of blue light (457 nm). Consequently, electron transfer from electron-rich amine to an oxidizing naphthoquinonyl biradical leads to a naphthoquinonyl radical anion and aminyl radical cation, followed by proton transfer and delocalization leading to a carbon-centered naphthoquinonyl radical. The cross-coupling of naphthoquinonyl carbon-centered and aminyl nitrogen radicals forms a C-N bond, with subsequent elimination of hydrogen gas (which was also confirmed by GC-TCD), affording 2-amino-1,4-naphthoquinone under metal-, reagent-, base-, and oxidant-free conditions.

t-BuOK mediated oxidative coupling amination of 1,4-naphthoquinone and related 3-indolylnaphthoquinones with amines

The transition-metal free amination of 1,4-naphthoquinone and related 3-indolylnaphthoquinones with amines, such as various (hetero)aromatic amine and aliphatic amine via t-BuOK-mediated oxidative coupling at room temperature has been developed. This reaction provides efficient access to the biologically important and synthetically useful 2-amino-1,4-naphthoquinones and 2-amino-3-indolylnaphthoquinones with good yields under mild conditions. The present protocol is simple, practical and shows good functional group tolerance. In addition, the obtained 2-amino-3-indolylnaphthoquinones were further transformed to synthesize polycyclic N-heterocycles.

Evaluation of cobalt(III) complexes as potential hypoxia-responsive carriers of esculetin

Differentiation between hypoxic and normoxic tissues have been exploited for the development of selective chemotherapeutic agents. In this context, cobalt(III)-based coordination compounds have been designed and investigated as prospective hypoxia-responsive drug delivery systems. Three cobalt(III) complexes, namely [Co^III(esc)(py₂en)]ClO₄·(CH₃OH)₂ (1) [Co^III(esc)(TPA)]ClO₄·3H₂O (2) and [Co^III(bipy)₂(esc)]ClO₄·2.5H₂O (3) (py₂en = N,N'-bis(pyridin-2-ylmethyl)ethylenediamine, TPA = tris(2-pyridylmethyl)amine, bipy = 2,2'-bipyridine and esc = 6,7-dihydroxycoumarin or esculetin), were prepared and investigated as potential carriers of esculetin. The spectroscopic and electrochemical properties of 1-3 were investigated and compared. Reactions of the complexes with biologically relevant reducing agents, viz. ascorbic acid, cysteine and glutathione, were monitored spectroscopically for 24 h, in pH 6.2 and 7.4 PBS phosphate buffer saline (PBS) solutions at 37 °C, under air, argon and dioxygen atmospheres. Dissociation of esculetin was observed upon Co³⁺/Co²⁺ reduction preferably under hypoxic conditions, with more effective conversion rates for 3 > 2 > 1. These results illustrate the importance to modulate the Co³⁺/Co²⁺ redox potential through the donor-acceptor properties of the ancillary ligands. Complex 3 is cytotoxic against HCT-116 but not against HT-29 and HEK-293 cells. In addition, DNA-binding studies indicate that interactions of 1 and 3 with the biomolecule are electrostatic.

Effect of ligand substituents on nickel and copper [N4] complexes: electronic and redox behavior, and reactivity towards protons

The ligand substituents have a major effect on the redox potentials, catalytic efficiency and robustness of the complexes in HER.

Aqua-(4,4'-bipyridine-κN)bis-(1,4-dioxo-1,4-dihydronaphthalen-2-olato-κO,O)zinc 4,4'-bipyridine mono-solvate dihydrate

The reaction of 2-hy­droxy-1,4-naphtho­quinone and 4,4′-bipyridine with zinc acetate produced the title compound, [Zn(C₁₀H₅O₃)₂(C₁₀H₈N₂)(H₂O)]·C₁₀H₈N₂·2H₂O. The bond lengths and angles around the metal atom indicate a deviation from octa­hedral geometry. The two naphtho­quinone ligands coordinate in a cis fashion, with the 4,4′-bipyridine ligand and the water mol­ecules completing the coordination sphere of the metal atom. The asymmetric unit contains also one free 4,4′-bipyridine mol­ecule and two uncoordinated water mol­ecules. These mol­ecules make contacts with the complex through O—H⋯N and O—H⋯O hydrogen bonds, creating a layer two-dimensional network parallel to (121).

Aminequinone-hydroxylquinoneimine tautomeric equilibrium revisited: molecular modeling study of the tautomeric equilibrium and substituent effects in 4-(4-R-phenylamino)naphthalene-1,2-diones

Semi-empirical (AM1 and PM3) and DFT (B3LYP/6-31G(d)) calculations were employed to study the tautomeric equilibrium between the aminequinone A and hydroxylquinoneimine B forms of 4-(4-R-phenylamino)naphthalene-1,2-diones. Substituent effects on the tautomeric equilibrium as well as on geometric and electronic parameters were also determined. In the gas phase the hydroxylquinoneimine B form is the most stable, whereas in water the aminequinone A form becomes more stable. The substituents do not modify the relative energies of the two tautomers. These results are in accordance with experimental data reported in the literature.