Recent syntheses of 1,2,3,4-tetrahydroquinolines, 2,3-dihydro-4(1H)-quinolinones and 4(1H)-quinolinones using domino reactions

Embracing heterogeneous photocatalysis: evolution of photocatalysts in annulation of dimethylanilines and maleimides

Recent advances in visible-light-promoted construction of tetrahydroquinolines from dimethylanilines and maleimides are documented. Homogeneous and heterogeneous photocatalytic systems, as well as the reaction mechanism, are emphasized. The mechanism of this photocatalytic annulation reaction is quite clear, i.e., dimethylanilines and maleimides serve as the radical precursors and radical acceptors, respectively. This annulation reaction could serve as an excellent platform for evaluating novel oxidative heterogeneous photocatalytic systems, which could further inspire chemists in this field to develop more efficient photocatalytic systems. Significant opportunities are expected in the future for heterogeneous photocatalysis strategies.

Copper-catalyzed dehydrogenative cyclization/alkenylation towards dihydroquinolinones

An efficient copper-catalyzed one-pot sequential synthesis of alkenylated quinolinyl dihydroquinolinones is reported, utilizing ketones, 1,3-cyclohexanediones, and benzyl alcohols via dehydrogenative cyclization, followed by alkenylation. This highly straightforward method provides a mild and environmentally friendly approach, and scalable reactions are carried out without generating side products. Furthermore, a plausible reaction mechanism is proposed based on control-experiment studies and reaction monitoring via1H NMR analysis. In addition, the photophysical behavior of the synthesized products showed various responses in the absorption and emission spectra. Upon further examination, compound 4F was found to have acidochromic properties, leading to noticeable colour changes.

Domino Aldol-SNAr-Dehydration Sequence for [3+3] Annulations to Prepare Quinolin-2(1H)-ones and 1,8-Naphthyridin-2(1H)-ones

A domino aldol-SNAr-dehydration [3+3] annulation strategy has been utilized to fuse six-membered cyclic amides onto aromatic substrates. 2-Arylacetamides have been reacted with 2-fluorobenzaldehyde derivatives activated toward SNAr reaction by an electron-withdrawing substituent (NO2, CN, CF3, CO2Me) at C5 to prepare 3,6-disubstituted quinolin-2(1H)-ones. Additionally, 3-substituted 1,8-naphthyridin-2(1H)-ones have been similarly derived from 2-fluoronicotinaldehyde. Fifteen examples are reported, and two possible mechanistic scenarios are presented and discussed.

The regioselective one-pot four-component synthesis of novel functionalized 4H-pyrano[2, 3-b]quinoline derivatives using DABCO as a homogeneous organocatalyst

This study deals with the synthesis of the regioselective and facile domino one-pot four-component reaction of 2-chloroquinoline-3-carbaldehydes, 1, 3-cyclodione compounds (as cyclic active methylene), ethyl acetoacetate (as β-keto ester), and hydrazine hydrate in the presence of DABCO as a homogeneous organocatalyst yielding a novel series of 4H-pyrano[2, 3-b]quinolones. This multicomponent reaction has some advantages; the significant one is C-O bond formation under metal-free conditions. Other benefits include simple procedure, mild and green condition, high yield, easy purification, and excellent regioselectivity. All polycyclic products (7a-k, 11 new compounds) were characterized by IR, 1H NMR, 13C NMR, and mass spectra.

Chalcogen-Bond Catalysis: Telluronium-Catalyzed [4+2]-Cyclocondensation of (in situ Generated) Aryl Imines with Alkenes

In the chalcogen series, tellurium species exhibit the strongest chalcogen bonding (ChB) interaction with electron-rich atom. This property explains the renewed interested toward tellurium-based derivatives and their use in different applications, such as organocatalysis. In this context, the catalytic activity of telluronium salts in the Povarov reaction is presented herein. Different dienophiles, as well as imines of variable electronic nature, efficiently react in the presence of catalytic amount of either diarylmethyltelluronium or triaryltelluronium salts. Both catalysts could also readily perform the three-component Povarov reaction starting from aldehyde, aniline and dihydrofuran. The reactivity of telluroniums towards imines and aldehydes was confirmed in the solid state by the ability of Te atom to interact through ChB with the oxygen carbonyl of acetone, and in solution with significant shift variations of the imine proton and of the tellurium atom in ¹ H and ¹²⁵ Te NMR spectroscopy. For the most active telluronium catalysts bearing CF₃ groups, association constants (K) with N-phenyl phenylmethanimine in the range 22-38 M^-1 were measured in dichloromethane.

Demystifying the potential of inhibitors targeting DNA topoisomerases in unicellular protozoan parasites

DNA topoisomerases are a group of enzymes omnipresent in all organisms. They maintain the DNA topology during replication, repair, recombination, and transcription. However, the structure of topoisomerase in protozoan parasites differs significantly from that of human topoisomerases; thus, this enzyme acts as a crucial target in drug development against parasitic diseases. Although the therapeutic potential of drugs targeting the parasitic topoisomerase is well known, to manage the shortcomings of currently available therapeutics and the emergence of drug resistance, the discovery of novel antiparasitic molecules is an urgent need. In this review, we describe various investigational and repurposed topoisomerase inhibitors developed against protozoan parasites over the past few years. Teaser: Fatal parasitic diseases are an increasing cause for concern; here, we provide a compilation of different inhibitors targeting DNA topoisomerases, enzymes that are essential for, and unique to, protozoan parasites; therefore, inhibitors are efficient and have few adverse effects.

Photoinduced Electron Donor-Acceptor Complex-Mediated Radical Cascade Involving N-(Acyloxy)phthalimides: Synthesis of Tetrahydroquinolines

We conceptualized a novel disconnection approach for the synthesis of fused tetrahydroquinolines that exploits a visible light-mediated radical (4 + 2) annulation between alkyl N-(acyloxy)phthalimides and N-substituted maleimides in the presence of DIPEA as an additive. The reaction proceeds through the formation of a photoactivated electron donor-acceptor complex between alkyl NHPI esters and DIPEA, and the final tetrahydroquinolines were obtained in a complete regioselective fashion. The methodology features a broad scope and good functional group tolerance and operates under metal- and catalyst-free reaction conditions. Detailed mechanistic investigations including density functional theory studies provide insight into the reaction pathway.

Design, Synthesis, and Antimycobacterial Evaluation of Novel Tetrahydroisoquinoline Hydrazide Analogs

A series of novel 2-substituted-5,7-dichloro-1,2,3,4-tetrahydroisoquinoline-6-carbohydrazide were designed, synthesized and structures were confirmed by analytical methods, viz., ¹ H-NMR, ¹³ C-NMR and Mass spectrometry. Synthesized derivatives were evaluated for their anti-mycobacterial activity against Mycobacterium tuberculosis (Mtb) H37Ra. Among all the evaluated compounds, 10A25 containing biphenyl moiety exhibited significant inhibition with IC₅₀ 4.7 μM. 10A19, with an electron-withdrawing Iodo group in the ortho position of the phenyl exhibited significant anti-tubercular activity with IC₅₀ 8.8 μM. IC₅₀ values of the remaining compounds ranged from 9.2 to 73.6 μM. Molecular docking study of the significantly active compound 10A25 was performed to determine the putative binding position of the test ligand at the active site of the selected target proteins Mycobacterium tuberculosis enoyl reductase (InhA) PDB - 4TZK and peptide deformylase PDB - 3E3U. A suitable single crystal for one of the active compounds, 10A12, was generated and analysed to further confirm the structure of the compounds.

Methyl 12-Methyl-3,9-dinitro-5,6,7,12-tetrahydro-13-oxodibenzo[b.g]bicyclo[3.3.1]nonane-6-carboxylate and Related Compounds

A synthesis of the title compound and related structures is reported. The procedure involves double alkylation of a β-ketoester followed by double SNAr ring closure from the γ carbon to give a dibenzo[3.3.1]bicyclic unit. This paper appears to be the first to generate a mid-sized bicyclic target by a double SNAr process. The synthesis can be performed in one step, but yields are superior (52–62%) when a two-stage procedure is used.

Chemoenzymatic Synthesis of Optically Active Alcohols Possessing 1,2,3,4-Tetrahydroquinoline Moiety Employing Lipases or Variants of the Acyltransferase from Mycobacterium smegmatis

The enzymatic kinetic resolution (EKR) of racemic alcohols or esters is a broadly recognized methodology for the preparation of these compounds in optically active form. Although EKR approaches have been developed for the enantioselective transesterification of a vast number of secondary alcohols or hydrolysis of their respective esters, to date, there is no report of bio- or chemo-catalytic asymmetric synthesis of non-racemic alcohols possessing 1,2,3,4-tetrahydroquinoline moiety, which are valuable building blocks for the pharmaceutical industry. In this work, the kinetic resolution of a set of racemic 1,2,3,4-tetrahydroquinoline-propan-2-ols was successfully carried out in neat organic solvents (in the case of CAL-B and BCL) or in water (in the case of MsAcT single variants) using immobilized lipases from Candida antarctica type B (CAL-B) and Burkholderia cepacia (BCL) or engineered acyltransferase variants from Mycobacterium smegmatis (MsAcT) as the biocatalysts and vinyl acetate as irreversible acyl donor, yielding enantiomerically enriched (S)-alcohols and the corresponding (R)-acetates with E-values up to 328 and excellent optical purities (>99% ee). In general, higher ee-values were observed in the reactions catalyzed by lipases; however, the rates of the reactions were significantly better in the case of MsAcT-catalyzed enantioselective transesterifications. Interestingly, we have experimentally proved that enantiomerically enriched 1-(7-nitro-3,4-dihydroquinolin-1(2H)-yl)propan-2-ol undergoes spontaneous amplification of optical purity under achiral chromatographic conditions.

Tetrahydroquinoline: an efficient scaffold as mTOR inhibitor for the treatment of lung cancer

Efforts have been made to find an efficient scaffold (and its substitution) that can be used for the treatment of lung cancer via mTOR inhibition. A detailed literature search was carried out for previously reported mTOR inhibitors. The present review is focused on lung cancer; therefore, descriptions of some mTOR inhibitors that are currently in clinical trials for the treatment of lung cancer are provided. Based on previous research findings, tetrahydroquinoline was found to be the most efficient scaffold to be explored for the treatment of lung cancer. A possible efficient substitution of the tetrahydroquinoline scaffold could also be beneficial for the treatment of lung cancer.

Organocatalytic Asymmetric Synthesis of Tetrahydroquinolines from ortho-Aminophenyl para-Quinone Methides

The asymmetric catalytic [4 + 2] cycloannulation of ortho-aminophenyl p-QMs with different types of alkenes for the construction of tetrahydroquinolines containing three contiguous stereogenic centers was developed. This is the first example of catalytic asymmetric cycloannulation of ortho-aminophenyl p-QMs. This reaction exhibits excellent functional group tolerance. Excellent yields, exclusive diastereoselectivities, and high enantioselectivities were obtained in this efficient organocatalytic reaction.

15.4.5 Quinolinones and Related Systems (Update 2022)

Quinolinones, of which the quinolin-4(1H)-one ring system can be highlighted, represent an exciting class of nitrogen heterocycles. The quinolinone motif can be found in many natural compounds and approved drugs for several diseases. This chapter is a comprehensive survey of the methods for the synthesis of quinolin-2(1H)-ones, quinolin-4(1H)-ones, and their thio- and amino derivatives, and is an update to the previous Science of Synthesis chapter (Section 15.4), covering the period between 2003 and 2020.

Visible-Light-Induced Synthesis of 1,2,3,4-Tetrahydroquinolines through Formal [4+2] Cycloaddition of Acyclic α,β-Unsaturated Amides and Imides with N,N-Dialkylanilines

1,2,3,4-Tetrahydroquinolines should be applicable to the development of new pharmaceutical agents. A facile synthesis of 1,2,3,4-tetrahydroquinolines that is achieved by a photoinduced formal [4+2] cycloaddition reaction of acyclic α,β-unsaturated amides and imides with N,N-dialkylanilines under visible-light irradiation, in which a new Ir^III complex photosensitizer, a thiourea, and an oxidant act cooperatively in promoting the reaction, is reported. The photoreaction enables the synthesis of a wide variety of 1,2,3,4-tetrahydroquinolines, while controlling the trans/cis diastereoselectivity (>99:1) and constructing contiguous stereogenic centers. A chemoselective cleavage of an acyclic imide auxiliary is demonstrated.

Synthesis of endo-fused 5-unsubstituted Hexahydro-2H-pyrano[3,2-c]quinolinesvia Sequential Sc(OTf)3-catalyzed Cationic Imino-Diels-Alder Reaction/N-debenzylation using N-benzylanilines, 3,4-dihydro-2H-pyran and Paraformaldehyde under MW Irradiation

BACKGROUND

Hexahydro-2H-pyrano[3,2-c]quinolines are known to have antibacterial, antifungal, and antitumor properties. Great efforts have been made to develop new synthetic methods that lead to the synthesis of valuable libraries. Extensive methodologies, low yields, excessive amounts of catalyst and expensive reactants are some of the limitations of current methodologies.

AIMS AND OBJECTIVE

Developing a useful and efficient method to construct diversely substituted hexahydro-2Hpyrano[ 3,2-c]quinolines into good to excellent yields through a cationic imino-Diels-Alder/N-debenzylation methodology.

METHOD

The cationic imino-Diels-Alder/N-debenzylation methodology was used for the preparation of substituted hexahydro-2H-pyrano[3,2-c]quinolines. It involves the use of Sc(OTf)₃ for activation of cationic imino- Diels-Alder cycloaddition reaction of N-benzylanilines, 3,4-dihydro-2H-pyran and paraformaldehyde in MeCN; and microwave irradiation to shorten reaction time to afford new 6-benzyl-hexahydro-2H-pyrano[3,2- c]quinolines whose catalytic transfer debenzylation reactions with HCO₂NH₄ in the presence of Pd/C (10%) and methanol give the new 5-unsubstituted pyrano[3,2-c]quinolines in excellent yields.

RESULTS

We found that optimal conditions for the preparation of hexahydro-2H-pyrano[3,2-c]quinolines were Sc(OTf)₃ 0.5 % and acetonitrile at 160°C for 15 min; and using paraformaldehyde obtained the 6-benzylhexahydro- 2H-pyrano [3,2-c]quinolines with excellent yields, while the N-debenzylation process using ammonium formate in the presence of Pd/C and methanol resulted in the synthesis of hexahydro-2H-pyrano [3,2-c] quinolines with quantitative yields (95-98%).

CONCLUSION

We describe an efficient method to synthesize hexahydro-2H-pyrano[3,2-c]quinolines via the cationic imino-Diels-Alder/N-debenzylation methodology using Sc(OTf)3 0.5 % as Lewis Acid catalyst. Excellent yields of the products, use of MW irradiation, short times of reactions, and an efficient and highly diversified method are some of the main advantages of this new protocol.

Kinetic resolution of 2-aryl-2,3-dihydroquinolin-4(1H)-one derivatives by rhodium-catalysed asymmetric transfer hydrogenation

An efficient rhodium-catalysed kinetic resolution of 2-aryl-2,3-dihydroquinolin-4(1H)-one derivatives through asymmetric transfer hydrogenation.

Tandem synthesis of tetrahydroquinolines and identification of the reaction network by operando NMR

Bifunctional MOF supported Pd nanoparticles for the one-pot tandem synthesis of substituted tetrahydroquinolines were developed, and operando high-pressure MAS-NMR were performed to understand the complex reaction network.

Ruthenium-catalyzed, site-selective C-H activation: access to C5-substituted azaflavanone

A site-selective ruthenium-catalyzed keto group assisted C–H bond activation of 2-aryl tetrahydroquinoline (azaflavanone) derivatives has been achieved with a variety of alkenes for the first time. A wide range of substrates was utilized for the synthesis of a wide variety of alkenylated azaflavanones. This simple and efficient protocol provides the C5-substituted azaflavanone derivatives in high yields with a broad range of functional group tolerance. Further, the C5-alkenylated products were converted into substituted 2-aryl quinoline derivatives in good yields.

A site-selective ruthenium-catalyzed keto group assisted C–H bond activation of 2-aryl tetrahydroquinoline (azaflavanone) derivatives has been achieved with a variety of alkenes for the first time.

Helquats as Promoters of the Povarov Reaction: Synthesis of 1,2,3,4-Tetrahydroquinoline Scaffolds Catalyzed by Helicene-Viologen Hybrids

Helquats (HQs) are structurally linked to helicenes and viologens, and they represent an attractive field of research in chemistry and medicinal chemistry. In the present work they were used as catalysts for the synthesis of 1,2,3,4-tetrahydroquinolines in good yields by the Povarov reaction. The substrate scope and the capability of different helquats to promote Povarov reactions are demonstrated. Studies to elucidate mechanistic details revealed that helquats act as single-electron transfer oxidants through a cation-radical mechanism. The screening of the catalytic activity of HQs confirmed that an active HQ must have a LUMO energy below -8.67 eV and the standard redox potential higher (less negative) than -1.2 V vs. the ferrocene/ferrocenium redox couple.

Oxidative Cyclization of o-(1-Hydroxy-2-alkynyl)-N-tosylanilides for the Synthesis of 4-Quinolones

The treatment of easily accessible o-(1-hydroxy-2-alkynyl)-N-tosylanilides 1 with excess manganese(IV) oxide in the presence of substoichiometric tetrabutylammonium iodide (TBAI) in chloroform (or in the absence of TBAI in dimethylformamide, DMF) promoted a sequential oxidation/intramolecular hydroamination to give 4-quinolones 3 and/or (Z)-2-alkylidene-3-oxindoles (Z)-4 in good yields. Possibly, MnO₂ played dual roles as an oxidant and as a Lewis acidic activator of intermediary ynones 2. The product distributions between 3 and (Z)-4 could be controlled by the choice of solvents.

Diastereoselective Construction of Cyclopropane-Fused Tetrahydroquinolines via a Sequential [4 + 2]/[2 + 1] Annulation Reaction

A sequential [4 + 2]/[2 + 1] annulation of α-aryl vinylsulfoniums with 2-aminochalcones and 2-(2-aminobenzylidene)-1H-indene-1,3(2H)-dione is reported that affords a series of cyclopropane-fused tetrahydroquinolines. The salient features of this novel and practical transformation include high efficiency, transition-metal-free nature, operational simplicity, and outstanding functional group tolerance.

Synthesis of highly substituted tetrahydroquinolines using ethyl cyanoacetate via aza-Michael-Michael addition

A three-component cascade reaction involving 2-alkenyl aniline, aldehydes, and ethyl cyanoacetate in the presence of DBU to synthesize highly substituted 1,2,3,4-tetrahydroquinolines is reported. The reaction proceeded through the Knoevenagel condensation of ethyl cyanoacetate with aldehydes followed by the aza-Michael-Michael addition with 2-alkenyl anilines to prepare the tetrahydroquinoline scaffolds.

Enantioselective Synthesis of 4-Allyl Tetrahydroquinolines via Copper(I) Hydride-Catalyzed Hydroallylation of 1,2-Dihydroquinolines

CuCl/(R,R)-Ph-BPE-catalyzed asymmetric hydroallylation of 1,2-dihydroquinolines, prepared from readily available quinolines, was developed. The optically active tetrahydroquinolines (THQs) bearing an allylic functionality at position 4 were obtained in good yields and excellent enantioselectivity. The introduced allylic groups are amenable to diverse transformations, thus offering chances to rapidly expand the THQ libraries.

Construction of piperidine-2,4-dione-type azaheterocycles and their application in modern drug development and natural product synthesis

The review surveys the existing routes to piperidine-2,4-dione-type heterocycles including derivatives with the most vital types of biological activity. This heterocyclic platform is ideal for the construction of modern drugs and natural products.

Organocatalyzed Synthesis of Functionalized Quinolines

As one of the most widely investigated compound skeleton, quinolines possess important medicinal and biological activities. As such, a great number of literatures, including reviews, have reported various methodologies to construct quinolines. Recently, organocatalyzed reactions have attracted the attention of organic chemists due to its being "green" because the reactions avoid the use of toxic metals. In this review, various distinctive contributions are surveyed with specific emphasis on organocatalyzed reactions for quinoline core constructions.

Selective C-H Olefination of Indolines (C5) and Tetrahydroquinolines (C6) by Pd/S,O-Ligand Catalysis

Herein, we report a highly selective C-H olefination of directing-group-free indolines (C5) and tetrahydroquinolines (C6) by Pd/S,O-ligand catalysis. In the presence of the S,O-ligand, a wide range of challenging indolines, tetrahydroquinolines, and olefins was efficiently olefinated under mild reaction conditions. The synthetic potential of this methodology was demonstrated by the efficient olefination of several indoline-based natural products.

Tetrahydroquinoline units in flexible heteroarotinoids (Flex-Hets) convey anti-cancer properties in A2780 ovarian cancer cells

SHetA2 (NSC 721689), our lead Flex-Het anti-cancer agent, consists of a thiochroman (Ring A) and a 4-nitrophenyl (Ring B) linked by a thiourea bridge. In this work, several series of new analogs having a tetrahydroquinoline (THQ, Ring A) unit connected by a urea or thiourea linker to a 4-substituted phenyl (Ring B) have been prepared and evaluated relative to SHetA2 in terms of binding affinity with mortalin and inhibition of A2780 ovarian cancer cells. Six of the derivatives equaled or exceeded the efficacy shown by SHetA2. Compounds 1a-d (series 1), lacking a methyl on the Ring A nitrogen and the gem-dimethyls on the adjacent carbon, showed only weak activity. Salt 2, the quaternized N,N-dimethyl iodide salt analog of 1a, also possessed very modest growth inhibition in the cell line studied. Series 3 compounds, which had a C3 ketone and an N-methyl replacing the sulfur in Ring A, were most successful. Compound 3a [Ring A = 1,2,2,4,4-pentamethyl-3-oxo-1,2,3,4-tetrahydroquinolin-6-yl; urea linker; Ring B = 4-nitrophenyl] had slightly lower potency (IC₅₀ 3.8 μM), but better efficacy (94.8%) than SHetA2 (IC₅₀ 3.17 μM, efficacy 84.3%). In addition, 3c and 3d [urea and thiourea linkers, respectively; Ring B = 4-(trifluoromethyl)phenyl] and 3e and 3f [urea and thiourea linkers, respectively; Ring B = 4-(trifluoromethoxy)phenyl] were also evaluated since these agents possessed electron-withdrawing groups with H-bonding capability. All displayed good activity. Compounds 3c and 3e showed improvement in both potency and efficacy compared to SHetA2. In general, when the linker group between Rings A and B was a urea, efficacy values slightly exceeded those with a thiourea linker in the carbonyl-containing THQ systems 3a-g. In contrast, when Ring A possessed the 1,2,2,4,4-pentamethyl-3-hydroxytetrahydroquinolin-6-yl unit (4a-f, series 4), very modest potency and efficacy was observed. Model compound 5, an exact N-methyl THQ analog of SHetA2, demonstrated less potency (IC₅₀ 4.5 μM), but improved efficacy (91.7%). Modeling studies were performed to rationalize the observed results.

Chiral Phosphoric-Acid-Catalyzed Cascade Prins Cyclization

Asymmetric Prins cyclization of in situ generated quinone methides and o-aminobenzaldehyde has been developed with chiral phosphoric acid as an efficient catalyst. This unconventional method provides a facile access to diverse functionalized trans-fused pyrano-/furo-tetrahydroquinoline derivatives in excellent yield and with excellent diastereo- and enantioselectivities (up to 99% yield and 99% ee). Mechanistic studies suggested that the three adjacent tertiary stereocenters were constructed through the sequential formation of C-O, C-C, and C-N bonds.

Heterogeneous Synergistic Catalysis for Promoting Aza-Michael–Henry Tandem Reaction for the Synthesis of Chiral 3-Nitro-1,2-Dihydroquinoline

Heterogeneous synergistic catalysis by SBA-15 immobilized chiral amines catalysts has promoted efficient aza-Michael–Henry tandem reaction for the synthesis of chiral 3-Nitro-1,2-Dihydroquinoline. Final products in the asymmetric aza-Michael–Henry cascade reactions between 2-aminobenzaldehyde and β-nitrostyrolene were afforded in a yield of 85% and an enantiomeric excess (ee) value of 98% on (S)-(–)-2-aminomethyl-1-ethylpyrrolidine immobilized SBA-15. SBA-15-AEP catalyst has been also extended to the asymmetric aza-Michael–Henry cascade reaction of substituted R1-2-aminobenzaldehyde and R2-substituted nitroolefin. The heterogeneous synergistic mechanism for both tertiary amine and secondary amine immobilized mesoporous has been proposed in detail including the geometrical constraints in the ee promotion.

Efficient synthesis and antioxidant activity of novel N-propargyl tetrahydroquinoline derivatives through the cationic Povarov reaction

New N-propargyl tetrahydroquinolines 6a-g have been synthesized efficiently through the cationic Povarov reaction (a domino Mannich/Friedel-Crafts reaction), catalyzed by Indium (III) chloride (InCl3), from the corresponding N-propargylanilines preformed, formaldehyde and N-vinylformamide, with good to moderate yields. All tetrahydroquinoline derivatives obtained were evaluated in vitro as free radical scavengers. Results showed that compound 6c presents a potent antioxidant effect compared with ascorbic acid, used as a reference compound. ADME predictions also revealed favorable pharmacokinetic parameters for the synthesized compounds, which warrant their suitability as potentials antioxidant. Additionally, a theoretical study using Molecular Quantum Similarity and reactivity indices were developed to discriminate different reactive sites in the new molecules in which the oxidative process occurs.

Enantioselective Synthesis of 4-Aminotetrahydroquinolines via 1,2-Reductive Dearomatization of Quinolines and Copper(I) Hydride-Catalyzed Asymmetric Hydroamination

A 1,2-reductive dearomatization of quinolines and copper(II) acetate monohydrate/( R, R)-Ph-BPE/P( p-tolyl)₃-catalyzed enantioselective hydroamination sequence was developed, affording diverse 4-amino-1,2,3,4-tetrahydroquinolines with high levels of enantioselectivity in either a stepwise or one-pot fashion. Pleasingly, internal cis-cyclic alkenes, which are challenging substrates in copper hydride-catalyzed enantioselective hydroamination reactions, were transformed efficiently under mild conditions.

Synthesis of Structurally Diverse 3-, 4-, 5-, and 6-Membered Heterocycles from Diisopropyl Iminomalonates and Soft C-Nucleophiles

Herein, we present a general synthetic strategy for the preparation of 3-, 4-, 5-, and 6-membered heterocyclic unnatural amino acid derivatives by exploiting facile Mannich-type reactions between readily available N-alkyl- and N-aryl-substituted diisopropyl iminomalonates and a wide range of soft anionic C-nucleophiles without using any catalyst or additive. Fully substituted aziridines were obtained in a single step when enolates of α-bromo esters were employed as nucleophiles. Enantiomerically enriched azetidines, γ-lactones, and tetrahydroquinolines were obtained via a two-step catalytic asymmetric reduction and cyclization sequence from ketone enolate-derived adducts. Finally, highly substituted γ-lactams were prepared in one pot from adducts obtained using acetonitrile-derived carbanions. Overall, this work clearly demonstrates the utility of iminomalonates as highly versatile building blocks for the practical and scalable synthesis of structurally diverse heterocycles.