Regioselective synthesis of 4-arylamino-1,2-naphthoquinones in eutectogel as a confined reaction medium using LED light

Predicting selectivity and conversion in a confined reaction medium under photochemical conditions is highly challenging as compared to the corresponding conventional synthesis. Herein, we report the use of a simple carbohydrate-derived eutectogel to facilitate LED-light-induced regioselective synthesis of 4-arylamino-1,2-naphthoquinones in good yield. This methodology, by including a reusable reaction medium, proved to have the potential of affording the regioselective formation of various desired products in good yields.

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.

Synthesis of Quinoline and Dihydroquinoline Embelin Derivatives as Cardioprotective Agents

A set of new dihydroquinoline embelin derivatives was obtained from the reaction of the natural benzoquinone embelin (1) with anilines and aromatic aldehydes in the presence of AgOTf. The synthesis of these compounds involves the formation of a Knoevenagel adduct, followed by nucleophilic addition of aniline and subsequent electrocyclic ring closure. The scope of the reaction regarding the aldehydes and anilines was determined. Quinoline derivatives were also obtained from the corresponding dihydroquinolines under oxidation with DDQ. The cardioprotective activity of the synthesized compounds was screened using a doxorubicin-induced cardiotoxicity model in H9c2 cardiomyocytes. Some structure-activity relationships were outlined, and the best activities were achieved with quinoline-embelin derivatives having a 4-nitrophenyl group attached at the pyridine ring. The obtained results indicated that embelin derivatives 4i, 6a, 6d, 6k, and 6m could have potential as cardioprotective agents, as they attenuated a DOX-induced cardiotoxicity effect acting on oxidative stress and apoptosis.

Multicomponent synthesis of styryl linked benzo[h]pyrazolo[3,4-b]quinoline-5,6(10H)-diones by liquid assisted grinding

Herein we report an interesting multicomponent reaction of α,β-unsaturated aldehydes, 2-hydroxy-1,4-naphthoquinone and 5-aminopyrazoles by liquid assisted grinding.

Biomimetic total syntheses of chromane meroterpenoids, guadials B and C, guapsidial A and psiguajadial D

The first biomimetic total syntheses of chromane meroterpenoids, guadials B and C, guapsidial A and psiguajadial D have been completed. The key synthetic transformation involves an efficient and high yielding hetero-Diels-Alder reaction. The two structurally isomeric natural products, guadials B and C, were obtained from a common o-quinone methide in the separate reactions with α-pinene and β-pinene, respectively. The two regioisomeric natural products, guapsidial A and psiguajadial D, were achieved in a single chemical operation.

Nano γ-Fe2O3-supported fluoroboric acid: a novel magnetically recyclable catalyst for the synthesis of 12-substituted-benzo[h][1,3]dioxolo[4,5-b]-acridine-10,11-diones as potent antitumor agents

Nano γ-Fe₂O₃-supported fluoroboric acid was synthesized as a novel magnetic catalyst, and was used for the efficient synthesis of benzoacridinediones.