Inverse Electron Demand Diels Alder Reaction of Aza-o-Quinone Methides and Enaminones: Accessing 3-Aroyl Quinolines and Indeno[1,2-b]quinolinones

We have developed a Diels Alder cycloaddition route toward 3-aroyl quinolines from enaminones and in situ generated aza-o-quinone methides. The reaction was found to be general with a range of substituted enaminones and aza-o-quinone methides, and we could validate the applicability of the methodology in gram scale. We also demonstrated a one-pot strategy toward 3-acyl quinolines starting from the corresponding aliphatic ketones. Finally, we utilized the 3-aroyl quinolines for synthesizing indeno[1,2-b]quinolinones via a Pd-catalyzed dual C-H activation approach.

Preparation of Chromeno[b]quinoline Derivatives and Their Application for Lipid Droplets Markers

Functional dyes with a chromeno[b]quinoline skeleton (3a-d) were synthesized by one-step cyclization between coumarin derivatives and aromatic amines under the promotion of anhydrous aluminum chloride in 41.2-45.8% yields. Their maximum absorption and emission wavelengths locate at 358-396 and 420-603 nm with large Stokes shifts (168-231 nm), and their intramolecular charge transfer has been corroborated by density functional theory calculations. Cell experiments have proved that the probes 3a-c possess the ability to target lipid droplets.

Domino Nitro Reduction-Friedländer Heterocyclization for the Preparation of Quinolines

The Friedländer synthesis offers efficient access to substituted quinolines from 2-aminobenzaldehydes and activated ketones in the presence of a base. The disadvantage of this procedure lies in the fact that relatively few 2-aminobenzaldehyde derivatives are readily available. To overcome this problem, we report a modification of this process involving the in situ reduction of 2-nitrobenzaldehydes with Fe/AcOH in the presence of active methylene compounds (AMCs) to produce substituted quinolines in high yields. The conditions are mild enough to tolerate a wide range of functionality in both reacting partners and promote reactions not only with phenyl and benzyl ketones, but also with β-keto-esters, β-keto-nitriles, β-keto-sulfones and β-diketones. The reaction of 2-nitroaromatic ketones with unsymmetrical AMCs is less reliable, giving a competitive formation of substituted quinolin-2(1H)-ones from the cyclization of the Z Knoevenagel intermediate which appears to be favored when certain large groups are adjacent to the AMC ketone carbonyl.

Synthesis of acridinones via palladium-catalyzed reductive annulation of 2-nitrobenzaldehydes and resorcinols

Through a palladium-catalyzed reductive annulation reaction of resorcinols and 2-nitrobenzaldehydes, reported is a new synthesis of acridinones with the features of operational simplicity, broad substrate scope, and readily available feedstocks.

Catalytic Acceptorless Dehydrogenation of Amino Alcohols and 2-Hydroxybenzyl Alcohols for Annulation Reaction under Neutral Conditions

A base-free and acceptorless Ru-catalyzed dehydrogenative approach has been developed for the synthesis of N-heterocycles by using 1,3-dicarbonyls and amino alcohols through a domino sequential enamine formation and intramolecular oxidative cyclization strategy. This unified approach is also applicable for the synthesis of O-heterocycles involving 2-hydroxybenzyl alcohol as a coupling reactant via consecutive C-alkylation and intramolecular cyclization steps. The present protocol is general for the synthesis of varieties of biologically important scaffolds, such as tetrahydro-4H-indol-4-one, 3,4-dihydroacridin-1(2H)-one, and tetrahydro-1H-xanthen-1-ones derivatives using a single catalytic system, viz. RuH₂CO(PPh₃)₃. Environmentally benign H₂O and H₂ are the only byproducts in this domino process. Moreover, RuH₂CO(PPh₃)₃-catalyzed C3-alkylation of tetrahydro-4H-indol-4-one using alcohol as a alkylating partner is also described in this report. For the first time, a solvent-free gram-scale reaction for the acceptorless dehydrogenative annulation has been demonstrated. A plausible mechanism for the Ru-catalyzed base-free and acceptorless dehydrogenative annulation of amino alcohols or 2-hydroxybenzyl alcohols has been provided with several experimental investigations and spectroscopic evidence.

The synthesis, biological evaluation and fluorescence study of chromeno[4,3-b]pyridin/quinolin-one derivatives, the backbone of natural product polyneomarline C scaffolds: a brief review

This review presents the synthesis, biological and fluorescence study of chromeno[4,3-b]pyridin/quinolin-ones via classical reactions including metal-catalyzed and green reaction protocols.

One-Pot Green Synthesis of Acridine Alkaloid Derivatives and Screening of in vitro Anti-cancer Activity Against Cdc25b and SHP1

AIM

To develop anti-cancer active pharmaceutical intermediates.

BACKGROUND

Acridone derivatives possess a wide range of pharmacological activities: 1) they intercalate DNA and 2) form a covalent bond with DNA.

OBJECTIVE

To screen in vitro anti-cancer activity against Cdc25b and SHP1 of new acridone derivatives and preliminary study on the structure-activity relationship.

MATERIALS AND METHODS

The synthesis of new acridone derivatives and in vitro evaluation of their anti-cancer activity on Cdc25b and SHP1 was achieved. Natural products that contain acridine structures, such as cystodytin A and acronycine, are isolated from certain marine (tunicates & ascidians, sponges, sea anemones) and plant (bark of Australian scrub ash tree) species. Herein, we report the efficient one-pot green synthesis of twelve novel 3,4-dihydro-1 (2H) acridone derivatives, using montmorillonite K10 as the catalyst and iron/citric acid in water. Also, their inhibitory activity against Cdc25B and SHP1 is examined, in which specific derivatives show enhanced inhibitory activity compared to others.

RESULTS AND DISCUSSION

Twelve new acridone derivatives were prepared, starting from 2-nitrobenzaldehyde derivatives and 1, 3-cyclohexanedione derivatives, which exhibited substantial anti-cancer activity against Cdc25b and SHP1 cells.

CONCLUSION

Preliminary studies on the structure-activity relationship have shown the influence of the structural parameters and, in particular, the nature of the substituent on aromatic ring structure and cyclohexanone. Other: Further study on the structure-activity relationship is required.

Aerobic, metal-free synthesis of 6H-chromeno[4,3-b]quinolin-6-ones

A Friedländer-based method for transition-metal free, aerobic synthesis of chromene-fused quinolinones is reported. The coupling of 4-hydrocoumarins and 2-aminobenzyl alcohols proceeds in the presence of acetic acid solvent and oxygen oxidant, affording 6H-chromeno[4,3-b]quinolin-6-ones in good to excellent yields. The reactions are tolerant of functionalities such as alkyl, methoxy, bromo, chloro, and N-heterocycle. Isosteric cyclic 1,3-diketones and 2-amino acetophenones also give fused quinolinones under reaction conditions. The method herein offers a rapid and benign synthesis of hitherto challenging N-heterocycles. To our best knowledge, such a convenient pathway to obtain chromene-fused quinolinones have not been known in the literature.

A Friedländer-based method for transition-metal free, aerobic synthesis of chromene-fused quinolinones is reported.

Catalytic formal [4 + 1] isocyanide-based cycloaddition: an efficient strategy for the synthesis of 1H-cyclopenta[b]quinolin-1-one derivatives

An unprecedented catalytic isocyanide-based cycloaddition of alkyl and aryl isocyanides with (Z)-2-(2-hydroxy-2-alkylvinyl)quinoline-3-carbaldehydes was developed for the direct and efficient synthesis of 1H-cyclopenta[b]quinolin-1-one derivatives. On the basis of DFT calculations, a mechanism is proposed involving formal [4 + 1] cycloaddition of isocyanides, followed by imine-enamine tautomerization and air oxidation.

Chemoselective and Highly Rate Accelerated Intramolecular Aza-Morita-Baylis-Hillman Reaction

Despite being a very useful C-C bond forming and highly applicative reaction, Morita-Baylis-Hillman (MBH) reaction has been limited by its excessive slow reaction rate, including its intramolecular version. In certain cases, reaction time may even go to weeks and months. A highly chemoselective and rate accelerated intramolecular MBH reaction of just 15 min has been developed. The product dihydroquinoline, being unstable, was converted to an important quinoline framework. In some cases IMBH adducts were isolable, thus confirming the reaction path. Control experiments toward mechanism investigation have been carried out. Use of sodium sulfide has emerged as a rate accelerating catalyst in DMF-EtOH solvent system. Reaction intermediate for IMBH pathway was isolated and characterized. Other aspects such as the application of IMBH adduct for Michael addition and amidation have also been carried out.

Synthesis and evaluation of 1,2,3,4-tetrahydro-1-acridone analogues as potential dual inhibitors for amyloid-beta and tau aggregation

Amyloid-β (Aβ) and tau protein are two crucial hallmarks in Alzheimer's disease (AD). Their aggregation forms are thought to be toxic to the neurons in the brain. A series of new 1,2,3,4-tetrahydro-1-acridone analogues were designed, synthesized, and evaluated as potential dual inhibitors for Aβ and tau aggregation. In vitro studies showed that compounds 25-30 (20 μM) with N-methylation of the quinolone ring effectively inhibited Aβ_1-42 aggregation by 84.7%-99.5% and tau aggregation by 71.2%-101.8%. Their structure-activity relationships are discussed. In particular, 30 could permeate the blood-brain barrier, bind to Aβ_1-42 and tau, inhibit Aβ_1-42 β-sheets formation, and prevent tau aggregation in living cells.

Transition metal-free one-pot double C-H functionalization of quinolines with disubstituted electron-deficient acetylenes

Transition metal-free one-pot reaction of quinolines with acylarylacetylenes and water proceeds in the presence of KOH (55-60 °C, MeCN, 48 h) to afford 2-aryl-3-acylquinolines in up to 66% yield. Here, a formal replacement of the acetylene moiety by the aryl and acyl substituents in the quinoline scaffold takes place. In fact, it has been proved experimentally that the reaction involves the ring cleavage, accompanied by the rearrangement and insertion of the electron-deficient acetylene moiety to form a dihydroquinoline intermediate with an aldehyde functional group in position 4. This intermediate gives the corresponding doubly functionalized quinolines.

Synthesis of quinolines via copper-catalyzed domino reactions of enaminones

Enaminones showcase synthetic utility for the synthesis of quinoline derivatives via copper-catalyzed domino reactions involving C–N bond formation, aldol reaction and dehydration.

Metal free TBHP-promoted intramolecular carbonylation of arenes via radical cross-dehydrogenative coupling: synthesis of indenoquinolinones, 4-azafluorenones and fluorenones

Analogues of indenoquinolinones, 4-azafluorenones and fluorenones were accessed in good to excellent yields. One of the synthesized derivative is known for antibacterial activity.

Ruthenium-catalysed C-alkylation of 1,3-dicarbonyl compounds with primary alcohols and synthesis of 3-keto-quinolines

Mono alkylation of 1,3-dicarbonyls is now possible with alcohols and catalytic amount of Hantzsch ester under Ru catalysis.

Pd catalyzed facile synthesis of cyclopenta[b]quinolin-1-one via sequential Sonogashira coupling and annulation. An unusual mode of ring closure, using sulphur as a soft nucleophile

Pd mediated one pot sequential Sonogashira coupling followed by annulation using o-alkynyl aldehyde is reported.

Syntheses of 4-Indolylquinoline Derivatives via Reductive Cyclization of Indolylnitrochalcone Derivatives by Fe/HCl

An easy and efficient procedure for the synthesis of 4-indolylquinoline derivatives is described. This process involves two steps, the first of which is the Michael addition of indole to nitrochalcones promoted by sulfamic acid under solvent free conditions and the second step is a reductive cyclization of the indolylnitrochalcone intermediates to 4-indolylquinoline derivatives by Fe/HCl in ethanol. In both steps, the reactions are clean and the yields of products are high.

Iron/acetic acid mediated synthesis of 6,7-dihydrodibenzo[b,j][1,7]phenanthroline derivatives via intramolecular reductive cyclization

An efficient iron/acetic acid mediated intramolecular reductive cyclization protocol was developed for the synthesis of novel 6,7-dihydrodibenzo[b,j][1,7]phenanthroline derivatives.