Pd(II)-Catalyzed tandem selective dehydrogenative [4+2] annulation of 2-methyl-1,3-cycloalkanediones with olefins

A practical and effective palladium-catalyzed selective dehydrogenative [4+2] annulation of 2-methyl-1,3-cycloalkanediones with olefins was reported. The active 2-methylene-1,3-cycloalkanedione was in situ generated via Pd-catalyzed enolate oxidation processes, and it subsequently reacted with a wide variety of olefins to afford various polysubstituted dihydropyran derivatives in good to excellent yields.

Phosphine-catalyzed [5+1] annulation of β'-acetoxy allenoates: straightforward access to tetrahydroquinoline derivatives

An unprecedented phosphine-catalyzed [5+1] annulation of β'-acetoxy allenoates with 1,5-dinucleophiles has been developed, which provides novel and facile access to functionalized tetrahydroquinolines in good to high yields in the presence of PPh3 and K3PO4 under mild reaction conditions. Notably, it is the first report of β'-acetoxy allenoates acting as C1 synthons in Lewis base-catalyzed annulation reactions.

Dearomatization of Cyclic Diphenylhydrazines: Harnessing the o-Semidine Rearrangement for the Synthesis of Spirocyclic Tetrahydroquinolines

The synthesis of novel tetrahydroquinoline-containing spirocycles has been achieved through an acid-promoted dearomatization of cyclic diarylhydrazines. The reaction, proceeding through a dearomative o-semidine rearrangement, furnishes a stable, yet reactive spirocyclohexadieniminium ion, which can further be used as an electrophile or a diene in a one-pot sequence. These transformations efficiently produce novel diazaspirocycles and allow for further synthetic elaboration of the cyclohexadienamine products.

Highly Enantioselective Three-Component Povarov Reaction for Direct Construction of Azaspirocycles

An asymmetric organocatalyzed three-component Povarov reaction to construct azaspirocycles has been developed. A chiral phosphoric acid OCF-CPA bearing o-CF₃-aryl on the H₈-BINOL-framework is highly efficient in the reaction. The reaction was carried out under mind conditions for synthesis of a range of azaspirocycles in high yields and high to excellent enantioselectivities, thus expending the substrate scope of the traditional Povarov reaction.

Ammonium iodide-catalyzed radical-mediated tandem cyclization of aromatic aldehydes, arylamines and 1,4-dioxane

We have developed a novel approach for the construction of 2-((2-arylquinolin-4-yl)oxy)ethan-1-ol derivatives involving a radical-mediated tandem cyclization reaction.

Synthesis, Characterization, and DFT Studies of N-(3,5-Bis(trifluoromethyl)benzyl)stearamide

The novel N-(3,5-bis(trifluoromethyl)benzyl)stearamide 3 was prepared in moderate yield by a solventless direct amidation reaction of stearic acid 1 with 3,5-bis(trifluoromethyl)benzylamine 2 at 140 °C for 24 h under metal- and catalyst-free conditions. This practical method was conducted in air without any special treatment or activation. The fatty acid amide 3 was fully characterized by IR, UV–Vis, 1D and 2D NMR spectroscopy, mass spectrometry, and elemental analysis. Moreover, molecular electrostatic potential studies, determination of quantum descriptors, fundamental vibrational frequencies, and intensity of vibrational bands were computed by density functional theory (DFT) using the B3LYP method with 6-311+G(d,p) basis set in gas phase. Simulation of the infrared spectrum using the results of these calculations led to good agreement with the observed spectral patterns.

3-(tert-Butyl)-N-(4-methoxybenzyl)-1-methyl-1H-pyrazol-5-amine

We reported an efficient one-pot two-step synthesis of 3-(tert-butyl)-N-(4-methoxybenzyl)-1-methyl-1H-pyrazol-5-amine 3 in good yield by a solvent-free condensation/reduction reaction sequence starting from 3-(tert-butyl)-1-methyl-1H-pyrazol-5-amine 1 and p-methoxybenzaldehyde 2. The one-pot reductive amination proceeded by the formation in situ of the N-(5-pyrazolyl)imine 4 as key synthetic intermediate of other valuable pyrazole derivatives. This methodology is distinguished by its operational easiness, short reaction time, isolation and purification of the aldimine intermediate is not required. The structure of the synthesized N-heterocyclic amine 3 was fully characterized by FTIR-ATR, 1D and 2D NMR experiments, EIMS, and elemental analysis.

Mechanochemical Aza-Vinylogous Povarov Reactions for the Synthesis of Highly Functionalized 1,2,3,4-Tetrahydroquinolines and 1,2,3,4-Tetrahydro-1,5-Naphthyridines

The aza-vinylogous Povarov reaction between aromatic amines, α-ketoaldehydes or α-formylesters and α,β-unsaturated dimethylhydrazones was carried out in a sequential three-component fashion under mechanochemical conditions. Following extensive optimization work, the reaction was performed on a vibratory ball mill operating at 20 Hz and using zirconium oxide balls and milling jar, and afforded 1,2,3,4-tetrahydroquinolines and 1,2,3,4-tetrahydro- 1,5-naphthyridines functionalized at C-2, C-4 and also at C-6, in the latter case. This protocol generally afforded the target compounds in good to excellent yields and diastereoselectivities. A comparison of representative examples with the results obtained under conventional conditions revealed that the mechanochemical protocol affords faster Povarov reactions in comparable yields using a solvent-less environment.

I2-Catalyzed oxidative dehydrogenative tandem cyclization of 2-methylquinolines, arylamines and 1,4-dioxane

A novel I2-catalyst oxidative dehydrogenative tandem cyclization of 2-methylquinolines, arylamines and 1,4-dioxane for the construction of 2-([2,2′-biquinolin]-3-yloxy)ethan-1-ol derivatives has been developed under metal-free conditions.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Hydrogen-bonding-assisted redox-neutral construction of tetrahydroquinolines via hydride transfer

The hydrogen-bonding-assisted construction of tetrahydroquinolines decorated with structurally diverse 3,3'-difunctional groups has been realized via a hydride transfer-involved three-step cascade reaction in the presence of morpholine. This protocol solves the limitation of acyclic 1,3-dicarbonyl compounds by one-pot synthesis of tetrahydroquinolines, featuring operational simplicity, broadly applicable substrates, and metal- and acid-free conditions with EtOH as a hydrogen-bonding donor.

Recent Progress in the Synthesis of Quinolines

BACKGROUND

Quinoline-containing compounds present in both natural and synthetic products are an important class of heterocyclic compounds. Many of the substituted quinolines have been used in various areas including medicine as drugs. Compounds with quinoline skeleton possess a wide range of bioactivities such as antimalarial, anti-bacterial, anthelmintic, anticonvulsant, antiviral, anti-inflammatory, and analgesic activity. Due to such a wide range of applicability, the synthesis of quinoline derivatives has attracted a lot of attention of chemists to develop effective methods. Many known methods have been expanded and improved. Furthermore, various new methods for quinoline synthesis have been established. This review will focus on considerable studies on the synthesis of quinolines date which back to 2014.

OBJECTIVE

In this review, we discussed recent achievements on the synthesis of quinoline compounds. Some classical methods have been modified and improved, while other new methods have been developed. A vast variety of catalysts were used for these transformations. In some studies, quinoline synthesis reaction mechanisms were also displayed.

CONCLUSION

Many methods for the synthesis of substituted quinoline rings have been developed recently. Over the past five years, the majority of those reported have been based on cycloisomerization and cyclization processes. Undoubtedly, more imaginative approaches to quinoline synthesis will appear in the literature in the near future. The application of known methods to natural product synthesis is probably the next challenge in the field.

Synthesis of Biologically Active Molecules through Multicomponent Reactions

Focusing on the literature progress since 2002, the present review explores the highly significant role that multicomponent reactions (MCRs) have played as a very important tool for expedite synthesis of a vast number of organic molecules, but also, highlights the fact that many of such molecules are biologically active or at least have been submitted to any biological screen. The selected papers covered in this review must meet two mandatory requirements: (1) the reported products should be obtained via a multicomponent reaction; (2) the reported products should be biologically actives or at least tested for any biological property. Given the diversity of synthetic approaches utilized in MCRs, the highly diverse nature of the biological activities evaluated for the synthesized compounds, and considering their huge structural variability, much of the reported data are organized into concise schemes and tables to facilitate comparison, and to underscore the key points of this review.

Visible-Light-Mediated Aerobic Tandem Dehydrogenative Povarov/Aromatization Reaction: Synthesis of Isocryptolepines

A metal‐free, photoinduced aerobic tandem amine dehydrogenation/Povarov cyclization/aromatization reaction between N‐aryl glycine esters and indoles leads to tetracyclic 11H‐indolo[3,2‐c]quinolines under mild conditions and with high yields. The reaction can be performed by using molecular iodine along with visible light, or by combining an organic photoredox catalyst with a halide anion. Mechanistic studies reveal that product formation occurs through a combination of radical‐mediated oxidation steps with an iminium ion or N‐haloiminium ion [4+2]‐cycloaddition, and the N‐heterocyclic products constitute new analogues of the antiplasmodial natural alkaloid isocryptolepine.

Transition metal-free cyclobutene rearrangement in fused naphthalen-1-ones: controlled access to functionalized quinones

The divergent preparation of 1,4-naphthoquinones and tetraphene-7,12-diones, which bear the ABCD-ring of landomycins, has been accomplished directly through oxidative reorganization of previously non-isolable cyclobuta[a]naphthalen-4(2H)-ones.

The dual alkylation of the C(sp3)–H bond of cyclic α-methyl-N-sulfonyl imines via the sequential condensation/hydride transfer/cyclization process

The dual alkylation of the C(sp³)–H bond of the cyclic α-methyl-N-sulfonyl imine has been achieved through the piperidine-promoted cascade condensation/[1,5]-hydride transfer/cyclization from cyclic α-methyl-N-sulfonyl imine and o-aminobenzaldehyde in trifluoroethanol.

Photoinduced iodine-mediated tandem dehydrogenative Povarov cyclisation/C–H oxygenation reactions

Visible light and iodine mediate dehydrogenative imine [4+2]-cycloaddition/C–H oxygenation reactions to furnish highly functionalised 3-quinolones under metal-free conditions.

Inverse-Electron-Demand oxa-Diels-Alder Reactions of α-Keto-β,γ-unsaturated Esters and α,β-Unsaturated Hydrazones

A concise synthetic method for dihydropyrans has been developed by inverse-electron-demand oxa-Diels-Alder reaction of α-keto-β,γ-unsaturated esters with α,β-unsaturated hydrazones as electron-rich olefins. This reaction is catalyzed by Eu(hfc)₃ and proceeds in an endo-selective manner. This umpolung cycloaddition affords a variety of substituted dihydropyrans stereoselectively in high yields. In addition, indirect synthesis of formyl-substituted dihydropyran was achieved by dehydrazonation of the cycloadduct. This method is expected to be useful for the synthesis of dihydropyrans and tetrahydropyrans with unusual substitution patterns.

Progress in the Chemistry of Tetrahydroquinolines

Tetrahydroquinoline is one of the most important simple nitrogen heterocycles, being widespread in nature and present in a broad variety of pharmacologically active compounds. This Review summarizes the progress achieved in the chemistry of tetrahydroquinolines, with emphasis on their synthesis, during the period from mid-2010 to early 2018.

Inverse-electron-demand Diels-Alder reactions of α,β-unsaturated hydrazones with 3-methoxycarbonyl α-pyrones

Inverse-electron-demand Diels-Alder reactions of 3-electron-withdrawing group substituted α-pyrones with α,β-unsaturated hydrazones as electron-rich counterparts are catalyzed by Eu(hfc)3 to afford bicyclic lactone cycloadducts. This is an example of umpolung cycloaddition based on functional transformation of carbonyls to hydrazones. A subsequent dehydrazonation reaction enables indirect synthesis of carbonyl group-containing bicyclic lactones, which cannot be easily obtained by the cycloaddition of α-pyrones and enals.

Asymmetric synthesis of tetrahydroisoquinoline-fused spirooxindoles as Ras-GTP inhibitors that inhibit colon adenocarcinoma cell proliferation and invasion

We report the synthesis of a library of chiral THIQ-fused spirooxindoles. The most potent compound inhibits Ras-GTP, ultimately leading to mitochondrial apoptosis.

One-Step Synthesis of Fully Functionalized Pyrazolo[3,4-b]pyridines via Isobenzofuranone Ring Opening

A novel series of fully substituted pyrazolo[3,4-b]pyridines 4 has been prepared in a regioselective manner by the microwave-assisted reaction between N-substituted 5-aminopyrazoles 1 and 3-(3-oxo-2-benzofuran-1(3H)-ylidene)pentane-2,4-dione (2). This is the second reported example of a cyclocondensation reaction using substrate 2 as a 1,3-bis-electrophilic reagent. Remarkably, this synthesis offers functionalized products with acetyl and carboxyl groups in one step, in good yields, and with short reaction times. Additionally, the cyclization intermediate 3 was isolated, allowing us to postulate a mechanism for this reaction, which is initiated via isobenzofuranone ring opening of 2 in a Michael-type reaction. The structures of the products and regioselectivity of the reactions were determined on the basis of NMR measurements and X-ray diffraction. For this new reaction using substrate 2, the optimal reaction conditions and its scope were investigated.

One-Pot Synthesis of Functionalized Carbazoles via a CAN-Catalyzed Multicomponent Process Comprising a C-H Activation Step

The microwave-promoted three-component reaction between o-nitrochalcones, primary amines and β-dicarbonyl compounds in the presence of Ce(IV) ammonium nitrate constitutes the first example of a multicomponent carbazole synthesis. This reaction furnishes highly substituted and functionalized carbazole derivatives via a double annulation process that generates two C-C and two C-N bonds, with water as the only side product. Mechanistically, this transformation has some unusual features that include an intramolecular coupled hydrogenation-dehydrogenation process, the functionalization of a C-H group by direct attack onto a nitrogen function and a CAN-catalyzed reduction via hydride transfer from ethanol. The mechanisms of these reactions were studied with the aid of computational techniques.

Leucine rich repeat kinase 2 (LRRK2) inhibitors based on indolinone scaffold: Potential pro-neurogenic agents

Leucine-rich repeat kinase 2 (LRRK2) is one of the most pursued targets for Parkinson's disease (PD) therapy. Moreover, it has recently described its role in regulating Wnt signaling and thus, it may be involved in adult neurogenesis. This new hypothesis could give rise to double disease-modifying agents firstly by the benefits of inhibiting LRRK2 and secondly by promoting adult neurogenesis. Herein we report, the design, synthesis, biological evaluation, SAR and potential binding mode of indoline-like LRRK2 inhibitors and their preliminary neurogenic effect in neural precursor cells isolated from adult mice ventricular-subventricular zone. These results open new therapeutic horizons for the use of LRRK2 inhibitors as neuroregenerative agents. Moreover, the indolinone derivatives here prepared, inhibitors of the kinase activity of LRRK2, may be considered as pharmacological probes to study the potential neuroregeneration of the damaged brain.

Regioselective three-component synthesis of 2,3-disubstituted quinolines via the enaminone modified Povarov reaction

The enaminone modified three-component Povarov reactions enable the regioselective synthesis of 2,3-disubstituted quinolines.