Synthesis of Pyrimidine Fused Quinolines by Ligand-Free Copper-Catalyzed Domino Reactions

Herein, we report two novel methods for the synthesis of pyrimidine fused quinolines using a one-pot C-C and C-N bond forming strategy from the reaction of 6-aminouracils with 2-bromobenzaldehydes or 2-bromobenzyl bromide derivatives in the presence of 10 mol % CuCl₂ without using any ligand. The reaction of 2-bromobenzaldehyde or its derivatives with 6-aminouracils in the presence of K₂CO₃ as base and a catalytic amount of CuCl₂ in DMF medium under microwave heating conditions provides corresponding pyrimidine fused quinoline derivatives in good yields within 30 min. Alternatively, pyrimidine fused quinoline derivatives have been synthesized from the reaction of 2-bromobenzyl bromides with 6-aminouracil derivatives in the presence of molecular oxygen, CuCl₂ (10 mol %), and K₂CO₃ as base in DMF under reflux conditions. Structures of all the products were unambiguously confirmed by spectroscopic techniques and by recording single crystal XRD of 3a.

Palladium-catalyzed dimerization of N-aryl propargylamines for the synthesis of 3-vinylquinolines

A straightforward method for the synthesis of polyfunctionalized quinolines from readily available N-aryl propargylamines under aerobic conditions was developed. It provides convenient access to a variety of synthetically and pharmaceutically important quinolines in moderate to good yields. Control experiments suggest that the cascade reaction might proceed via the Pd-catalyzed electrophilic cyclization of N-aryl propargylamines followed by a hydroarylation process through trapping of the σ-quinolinylpalladium intermediate with a second molecule of the substrate.

Synthesis of quinolines and naphthyridines via catalytic retro-aldol reaction of β-hydroxyketones with ortho-aminobenzaldehydes or nicotinaldehydes

A Cu(i)-catalyzed retro-aldol reaction of β-hydroxyketones with ortho-aminobenzaldehydes and nicotinaldehydes is reported that produces a range of quinolines and naphthyridines with high efficiency and selectivity. This reaction uses β-hydroxyketones as a regiospecific ketone-protected enolate source via copper-catalyzed retro-aldol C_α-C_β bond cleavage. The in situ generated copper enolate undergoes kinetically favorable cyclization with ortho-amino aryl aldehydes to produce quinolines and naphthyridines in a chemo- and regioselective manner. The mild and weakly basic reaction conditions also suppress possible side reactions of benzaldehydes under strongly basic conditions, resulting in improved reaction yields.

Base-Controlled Regioselective Functionalization of Chloro-Substituted Quinolines

We prepared a number of di- and trifunctionalized quinolines by selective metalation of chloro-substituted quinolines with metal amides followed by reaction with different electrophiles. Metalation of the C-3 position of the quinolinic ring with lithium diisopropylamide at -70 °C is easy to achieve, whereas reaction with lithium-magnesium and lithium-zinc amides affords C-2 or C-8 functionalized derivatives in a regioselective fashion. These complementary methods could be rationalized by DFT calculations and are convenient strategies toward the synthesis of bioactive quinoline derivatives such as chloroquine analogues.

Photoredox-catalyzed cascade addition/cyclization of N-propargyl aromatic amines: access to 3-difluoroacetylated or 3-fluoroacetylated quinolines

3-Difluoroacetylated quinolines and 3-fluoroacetylated quinolines were synthesized via a visible-light-induced cascade addition/cyclization of N-propargyl aromatic amines catalyzed by fac-Ir(ppy)₃ under mild conditions.

tert-Butyl peroxybenzoate mediated formation of 3-alkylated quinolines from N-propargylamines via a cascade radical addition/cyclization reaction

A novel method for constructing 3-alkylated quinolines was developed via tert-butyl peroxybenzoate mediated cycloaddition between N-propargyl aromatic amines and ethers.

Acid-promoted iron-catalysed dehydrogenative [4 + 2] cycloaddition for the synthesis of quinolines under air

An acid-promoted iron-catalysed dehydrogenative [4 + 2] cycloaddition reaction was developed for the synthesis of quinolines using air as a terminal oxidant. Various quinoline derivatives were obtained, and no other byproducts besides water.

One-pot regioselective synthesis of 2,4-disubstituted quinolines via copper(ii)-catalyzed cascade annulation

A copper(ii)-catalyzed cascade annulation for the one-pot synthesis of 2,4-disubstituted quinolines has been disclosed.

Antiproliferative activity of new 2-glyco-3-nitro-1,2-dihydroquinolines and quinolines synthesized under solventless conditions promoted by neutral alumina

This paper describes the syntheses of new 2-glyco-3-nitro-1,2-dihydroquinolines and 2-glyco-3-nitroquinolines by one-pot aza-Michael–Henry-dehydration reactions using green procedures, as well as the evaluation of their antiproliferative activity.

Direct thiolation of aza-heteroaromatic N-oxides with disulfides via copper-catalyzed regioselective C–H bond activation

A novel and efficient thiolation reaction of aza-heteroaromatic N-oxides with disulfides via copper catalyzed C–H activation has been developed.

Brønsted Acid-Catalysed Allylic Amination of 1-(2-Aminoaryl)prop-2-en-1-ols to 1,2-Dihydroquinolines

A highly efficient synthetic method to prepare 1,2-dihydroquinolines that relies on trifluoromethanesulfonic acid (TfOH)-catalysed allylic amination of 1-(2-aminoaryl)prop-2-en-1-ols is described. Achieved at a catalyst loading of 0.01 mol-% under mild conditions at room temperature, the reaction was found to be robust, with a wide range of substitution patterns tolerated. The corresponding N-heterocyclic adducts were obtained in good to excellent yields of 45–93 %.

Organo-Photoredox Catalyzed Oxidative Dehydrogenation of N-Heterocycles

We report here for the first time the catalytic oxidative dehydrogenation of N-heterocycles by a visible-light organo-photoredox catalyst with low catalyst loading (0.1-1 mol %). The reaction proceeds efficiently under base- and additive-free conditions with ambient air at room temperature. The utility of this benign approach is demonstrated by the synthesis of various pharmaceutically relevant N-heteroarenes such as quinoline, quinoxaline, quinazoline, acridine, and indole.

An Efficient One-Pot Synthesis of Densely Functionalized Fused-Quinolines via Sequential Ugi4CC and Acid-Mediated Povarov-Type Reaction

A divergent synthesis of fused-quinolines has been explored by performing Ugi four-component condensation and sulfuric acid promoted deprotection/Povarov-type reaction in one-pot. The process involves Ugi condensation of propiolic acids, aldehydes/ketones, aminoaldehyde acetals and isocyanides followed by sulfuric acid promoted deprotection and Povarov-type reaction with anilines in ethanol. This method enables straightforward access to the structurally diverse 2,3-dihydro-1H-pyrrolo[3,4-b]quinolin-1-ones (DHPQ), 3,4-dihydrobenzo[b][1,6]naphthyridin-1(2H)-ones (DHBN), and 2,3,4,5-tetrahydro-1H-azepino[4,3-b]quinolin-1-ones (THAQ), starting from readily available starting materials.

The Beneficial Sinergy of MW Irradiation and Ionic Liquids in Catalysis of Organic Reactions

The quest for sustainable processes is becoming more and more important, with catalysis playing a major role in improving atom economy and reducing waste. Organic syntheses with less need of protecting/de-protecting steps are highly desirable. The combination of microwave irradiation, as energy source, with ionic liquids, as both solvents and catalysts, offered interesting solutions in recent years. The literature data of the last 15 years concerning selected reactions are presented, highlighting the importance of microwave (MW) technology coupled with ionic liquids.

Inhibitors of the Detoxifying Enzyme of the Phytoalexin Brassinin Based on Quinoline and Isoquinoline Scaffolds

The detoxification of the phytoalexin brassinin to indole-3-carboxaldehyde and S-methyl dithiocarbamate is catalyzed by brassinin oxidase (BOLm), an inducible fungal enzyme produced by the plant pathogen Leptosphaeria maculans. Twenty-six substituted quinolines and isoquinolines are synthesized and evaluated for antifungal activity against L. maculans and inhibition of BOLm. Eleven compounds that inhibit BOLm activity are reported, of which 3-ethyl-6-phenylquinoline displays the highest inhibitory effect. In general, substituted 3-phenylquinolines show significantly higher inhibitory activities than the corresponding 2-phenylquinolines. Overall, these results indicate that the quinoline scaffold is a good lead to design paldoxins (phytoalexin detoxification inhibitors) that inhibit the detoxification of brassinin by L. maculans.

Predictive Model for Site-Selective Aryl and Heteroaryl C-H Functionalization via Organic Photoredox Catalysis

Direct C-H functionalization of aromatic compounds is a useful synthetic strategy that has garnered much attention because of its application to pharmaceuticals, agrochemicals, and late-stage functionalization reactions on complex molecules. On the basis of previous methods disclosed by our lab, we sought to develop a predictive model for site selectivity and extend this aryl functionalization chemistry to a selected set of heteroaromatic systems commonly used in the pharmaceutical industry. Using electron density calculations, we were able to predict the site selectivity of direct C-H functionalization in a number of heterocycles and identify general trends observed across heterocycle classes.

Preparation of 3-Iodoquinolines from N-Tosyl-2-propynylamines with Diaryliodonium Triflate and N-Iodosuccinimide

4-Aryl and 4-alkyl substituted 3-iodoquinolines could be smoothly obtained in one pot by treating N-tosyl-2-propynylamines with diaryliodonium triflate in the presence of K₃PO₄ and a catalytic amount of CuCl at room temperature, followed by treatment with N-iodosuccinimide and BF₃·OEt₂ at 0 °C, and then NaOH in methanol solution. The product, 3-iodo-4-phenylquinoline was smoothly transformed into 4-phenylquinoline with zinc; 4-phenyl-3-toluenesulfenylquinoline with toluenethiol, K₂CO₃, and CuI; 4-phenyl-3-phenylethynylquinoline with the Sonogashira coupling reaction; 4-phenyl-3-styrylquinoline with the Heck coupling reaction; 3,4-diphenylquinoline with the Suzuki-Miyaura coupling reaction; 2-cyclohexyl-3-iodo-4-phenylquinoline with cyclohexanecarboxylic acid, Ag₂CO₃, and K₂S₂O₈; and 3-iodo-2-(2',5'-dioxan-1'-yl)-4-phenylquinoline with benzoyl peroxide in dioxane.

Transition-metal-free synthesis of 3-(1-pyrrolidinyl)quinolines and 3-(1-pyrrolidinyl)quinoline 1-oxides via a one-pot reaction of 3-(1-pyrrolidinyl)crotonates with nitrobenzenes

A carbanion of tert-butyl 3-(1-pyrrolidinyl)crotonate adds to nitrobenzenes to form σ^H-adducts, which in the presence of pivaloyl chloride and triethylamine are converted into 3-(1-pyrrolidinyl)quinolines or 3-(1-pyrrolidinyl)quinoline 1-oxides depending on the nitrobenzene structure. This is the first methodology in which a quinoline ring is constructed from a substrate bearing a pyrrolidinyl ring. Starting from optically pure enamines, the method allows synthesis of the corresponding chiral products without racemisation.

Lewis Acid Catalyzed Dehydrogenative Coupling of Tertiary Propargylic Alcohols with Quinoline N-Oxides

An unprecedented Lewis acid catalyzed, high-efficiency synthesis of valuable 2-(quinolin-2-yl)prop-2-en-1-ones via dehydrogenative coupling of propargylic alkynols with quinoline N-oxides is described. This protocol, which tolerates a broad range of functional groups, provides a straightforward pathway to the products 2-(quinolin-2-yl)prop-2-en-1-one scaffolds in satisfactory yields. The conversion could be scaled up to gram scale efficiently, which underlines a latent application of this methodology.

Synthesis of 3-acylquinolines through Cu-catalyzed double C(sp3)–H bond functionalization of saturated ketones

A novel synthesis of 3-acylquinolines through Cu-catalyzed one-pot reactions of 2-aminoaryl aldehydes/ketones with inactivated ketones featured with double C(sp³)–H bond functionalization is presented.

Copper(ii) catalyzed domino synthesis of quinoline derivatives from arylamines and alkynes

An open-flask copper(ii) catalyzed quinoline synthesis by anilines and electron-deficient alkynes at room temperature has been developed.

A novel environmentally sustainable synthesis of Au–Ag@AgCl nanocomposites and their application as an efficient and recyclable catalyst for quinoline synthesis

An eco-friendly synthesis of Au–Ag@AgCl NCs was described using the tuber extract of Nephrolepis cordifolia. The synthetic utility of the NCs was demonstrated by the synthesis of pharmaceutically important quinoline derivatives.

Synthesis of 4-substituted 3-(2-hydroxyphenyl)-quinolines through an unexpected iron(iii) chloride promoted reaction of cyclic imine dibenzo[b,f][1,4]oxazepines with alkynes

An unexpected FeCl₃-promoted reaction of cyclic imine dibenzo[b,f][1,4]oxazepines with alkynes was studied to produce novel 4-substituted 3-(2-hydroxyphenyl)-quinolines with 34–88% yield.

Temperature switchable Brønsted acid-promoted selective syntheses of spiro-indolenines and quinolines

A high-yielding, temperature switchable divergent approach towards the synthesis of either spiro-indolenines or quinolines is described, starting from easily available indolyl ynones.