Pyran Annulated Heterocyclic Research Articles

Ionic Liquid-promoted the Synthesis of Structurally Diverse Pyrans, Pyran-annulated Heterocycles, and Spiropyrans

Abstract: During the last two decades, non-conventional solvents, especially various ionic liquids, have been utilized as efficient reaction media as they can play a dual role as solvents and promoters. The use of ionic liquids as a medium increases the efficiency of the reactions due to their inherent features like high thermal stability, ability to act as a catalyst, non-volatility, high polarity, reusability, ability to dissolve a large number of organic and inorganic compounds, etc. Under this direction, various structurally diverse ionic liquids have been employed as efficient reaction media for various organic transformations. On the other hand, among many other important synthetic scaffolds, during the last two decades, the synthesis of pyrans, pyran-annulated heterocyclic scaffolds, and spiropyrans have gained huge attention as they possess a wide range of significant biological efficacies, which include antibacterial, anticancer, antimycobacterial, antioxidant, xanthine oxidase inhibitory, etc. activities. Almost every day, many new methods are being added to the literature related to synthesizing pyrans, pyran- annulated heterocyclic scaffolds, and spiropyrans. Among many other alternatives, various ionic liquids have also played an efficient role as promoters for synthesizing structurally diverse pyrans, pyran-annulated heterocyclic scaffolds, and spiropyrans. In this review, we have summarized a large number of literature reported during the last two decades related to the ionic liquid-promoted synthesis of pyrans, pyran-annulated heterocyclic scaffolds, and spiropyran derivatives.

Glycine Catalyzed One-Pot Three-Component Synthesis of Structurally Diverse 2-Amino Substituted Pyran Annulated Heterocycles in Aqueous Ethanol under Refluxed Conditions

INTRODUCTION: A facile, convenient and general method has been developed for the one-pot three-component synthesis of structurally diverse 2-amino pyran annulated heterocycles from the reactions of aromatic aldehydes, malononitrile and various C-H activated acids in the presence of a catalytic amount of glycine as an efficient metal-free organocatalyst in aqueous ethanol under refluxed conditions. METHOD: Using this developed protocol, we were able to synthesize a series of structurally diverse 2-amino pyran derivatives viz., 2-amino-4,5-dihydropyrano[3,2-c]chromenes, 2-amino-4,5-dihydropyrano[4,3-b]pyrans, 2-amino-5,6,7,8-tetrahydro-4H-chromenes, 2'-amino-2,5'-dioxo-5'H-spiro[indoline-3,4'-pyrano[3,2-c]chromene]-3'-carbonitrile and 2'-amino-1,3,5'-trioxo-1,3-dihydro-5'H-spiro[indene-2,4'-pyrano[3,2-c]chromene]-3'-carbonitrile in excellent yields. RESULT: Synthesis of biologically promising pyrans and spiropyrans, high atom economy, excellent yields, use of metal-free catalyst, less toxic solvents, no chromatographic column purifications, multiple carbon-carbon and carbon-heteroatom bond formations are some of the major advantages of this newly developed protocol.

Chickpea Leaf Exudates: A Highly Efficient Natural Brønsted Acidic Medium for the Synthesis of Pyran-annulated Heterocycles

Abstract:We reported Chickpea leaf exudates (CLEs) as a Brønsted acid, naturally available biodegradable, eco-friendly, and reusable reaction medium for highly efficient and facile one-pot synthesis of pyran-annulated heterocyclic systems, like 7-aryl-benzopyrano[4,3-b]benzopyran-6,8- diones,tetrahydrobenzo[b]pyran, and dihydropyrano[c]chromenes scaffolds. The analogous products were obtained via tandem Knoevengel-Michael addition and cyclo condensation reaction in ethanol at room temperature with 90-96% yields in a short reaction time. Moreover, the reaction media containing Bronsted acids can be easily recovered and reused up to five times, slightly decreasing product yields.

Chitosan‐ZnO: An Efficient and Recyclable Polymer Incorporated Hybrid Nanocatalyst to Synthesize Tetrahydrobenzo[b]pyrans and Pyrano[2,3‐d]pyrimidinones under Microwave Expedition

AbstractThe innovation of facile, efficient and mild procedures utilizing contemptible, conveniently separable and reusablesolid catalysts that overcome obstacles are invariably in demand. Hence, a straightforward one‐pot multicomponent reaction (MCR) and an expedient procedure for the synthesis of pyran annulated heterocycles 5 a–k and 6 l–v is developed using Chitosan‐Zinc oxide (CS‐ZnO) hybrid nanocatalyst. Use of aqueous medium is one of the major highlight of the present protocol. This protocol renders ease of operation, facile work up and magnified yields (90–95 %) as well as explores the use of modified polymeric substrates in the organic synthesis.

Tertiary amine-bisquaternary ammonium functionalized polyacrylonitrile fiber for catalytic synthesis of pyran-annulated heterocycles

Polyacrylonitrile fiber supported bisquaternary ammonium salts with varying interchain quaternary ammonium (QA) to tertiary amine (TA) ratio, counter ions and linker groups were prepared and characterized by TGA, FTIR, XPS, XRD, SEM, EA and water contact angle. The functionalized fibers were used to catalyze three-component reaction (3CR) and tandem deacetalization-3CR for the synthesis of pyrano[4,3-b]pyrans, pyrano[3,2-c]chromenes and pyrano[3,2-c]quinolines in ethanol-water mixture. Under varying reaction conditions such as time, temperature, catalyst amount and solvents, the catalytic ability of the prepared fiber catalyst was investigated. Under the optimum conditions, the bisquaternary ammonium fiber with acetate counter ion and an interchain QA to TA ratio of 1:1 (PANBQAcF) showed the best catalytic activity among the prepared fiber catalysts, and it can be used for 10 runs consecutively with only a slight depreciation in catalytic activity. Interestingly, PANBQAcF can efficiently catalyze tandem deacetalization-Knoevenagel reaction and the relevant novel tandem deacetalization-3CRs for the synthesis of pyran-annulated heterocycles. In the tandem deacetalization reactions, the acetate ion plays an important role of facilitating proton transfer, which makes PANBQAcF a cooperative and reusable heterogeneous catalyst.

One-pot synthesis of 2-amino-3-cyano-4H-pyrans and pyran-annulated heterocycles using sodium citrate as an organo-salt based catalyst in aqueous ethanol

Sodium citrate as a highly efficient catalyst is developed for the synthesis of functionalized 2-amino-3-cyano-4H-pyrans and pyran-annulated heterocycles. This method involves a one-pot three-component reaction of aromatic aldehydes, malononitrile and 1,3-dicarbonyl compounds with EtOH: H2O (1:1 v/v) as solvent under room temperature. This protocol presents several advantages such as shorter reaction time, utilization of eco-friendly solvents, operational simplicity, mild reaction conditions, and maximum product yield. Moreover, the use of sodium citrate as an easily available, cheap and benign catalyst plays a pivotal role from a green perspective, considering its high recyclability and easy recovery. Therefore, this present methodology offers numerous possibilities in terms of large-scale industrial syntheses or application to numerous organic conversions. Furthermore, theoretical studies on the mechanistic pathway of the formation of product 4aa were also carried out to determine the catalytic role of sodium citrate on the feasibility of the reaction with DFT method, using B3LYP functional.

LUDOX HS-40 Catalyzed Pot, Atom and Step Economic (PASE) Synthesis of Pyran Annulated Heterocyclic Scaffolds

A simple pot, atom and step economic (PASE) synthesis of 2-amino-3-aroyl-4-aryl-tetrahydro-5H-chromen-5-one and hitherto unreported 2-amino-3-aroyl-4-aryl-dihydro-pyrano[3,2-c]chromen-5-one, 2-amino-3-aroyl-dihydrospiro[chromene-4,3'-indoline]-2',5(6H)-dione, 2-amino-3-aroyl-dihydro-5H-spiro[cyclopenta[b]pyran-4,3'-indoline]-2',5-dione, and 2'-amino-3'-aroyl-dihydro-2H-spiro[acenaphthylene-1,4'-chromene]-2,5'(6'H)-dione has been developed using LUDOX HS-40, a commercially available innocuous and inexpensive catalyst via direct annulations of benzoylacetonitrile, aldehyde/isatin/acenaphthoquinone and dimedone/cyclicdiketone/4-hydroxycoumarins in ethanol. This protocol offers advantages such as wide range of substrate scope, operational simplicity, higher yields, and cost-effectiveness.

Nano-pistachio hull-OxTiCl4 − x: synthesis, characterization and application as an effective and novel nanocatalyst for one-pot synthesis of dihydropyrano[3,2-b]chromenedione derivatives

According to the Food and Agriculture Organization (FAO), Iran is the largest pistachio (Pistacia vera) producer in the world. Nevertheless, pistachio by-products (PBs) contain a high level of phenolic and cellulose compounds, it can be used as a substrate for the preparation of solid acid catalysts. In this work, the novel pistachio hull-OxTiCl4 − x catalyst was synthesized via preparing pistachio hull, product of Kerman, as a support followed by treatment with titanium tetrachloride (TiCl4) and identified by Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (EDX), thermogravimetric analysis (TG), Brunauer–Emmett–Teller (BET) and X-ray powder diffraction (XRD). The size of the nano-pistachio hull-OxTiCl4 − x nanocatalyst was shown by a scanning electron microscope below 100 nm. The catalytic activity of the solid acid catalyst has been successfully examined in a one-pot, three-component condensation reaction of aromatic aldehydes, dimedone and kojic acid in refluxing ethanol to furnish dihydropyrano[3,2-b]chromendione derivatives. Consequently, pyran annulated heterocycles were obtained. The proposed approach has some advantages as excellent yields, mild reaction conditions, short reaction times, use of agricultural waste and eco-friendly.

One-Pot Access to Diverse Functionalized Pyran Annulated Heterocyclic Systems Using SCMNPs@BPy-SO3H as a Novel Magnetic Nanocatalyst

The SCMNPs@BPy-SO3H catalyst was prepared and characterized using Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Vibrating Sample Magnetometry (VSM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Afterwards, its capability was efficiently used to promote the one-pot, three-component synthesis of pyrano[2,3-c]pyrazole and 2-amino-3-cyano-pyrano[3,2-c]chromen-5(4H)-one derivatives. The strategy resulted in the desired products with excellent yields and short reaction times. The SCMNPs@BPy-SO3H catalyst was readily recovered using a permanent magnetic field and it was reused in six runs with a slight decrease in catalytic activity. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Uric Acid as a Naturally Biodegradable and Reusable Catalyst for the Convenient and Eco-Safe Synthesis of Biologically Active Pyran Annulated Heterocyclic Systems

A naturally biodegradable, reusable, and eco-safe catalyst, i.e., uric acid was developed and exploited for the green, facile and economical one-pot synthesis of pyran annulated heterocyclic systems from starting materials. This method gives an insight into the credibility of pathway followed by the aforementioned green and reusable catalyst in aiding the heterocyclic compounds formation. High atom economy, cleaner reaction profile, simple column-free work up condition, shorter reaction times, high to excellent yields, eco-safe and high catalytic activity make this present procedure an interesting alternative to the multistep approaches.

Expeditious Synthesis of 2-Amino-4H-chromenes and 2-Amino-4H-pyran-3- carboxylates Promoted by Sodium Malonate.

Chromenes and pyran annulated heterocycles are the most common frameworks existing in various biologically active molecules. Due to their beneficial and biological properties, they are eyecatching synthetic targets in the arsenal of organic chemistry. Thus, finding green and efficient methods, as well as searching for a new catalyst for the synthesis of these heterocycles is of interest to organic chemistry researchers. Sodium malonate as a readily available catalyst was employed aimed at the multicomponent synthesis of numerous 2-amino-4H-chromenes and 2-amino-4H-pyrans in water as a green medium reaction. The reaction was performed via treatment of aldehydes (1 mmol) with malononitrile/ethyl cyanoacetate (1 mmol) and β-dicarbonyl compounds (1 mmol)/or resorcinol (1 mmol) in water (4 mL) in the presence of sodium malonate (10 mol %) at 70°C. On completion of the reaction (monitored by TLC analysis), the reaction mixture was gradually cooled at room temperature, and the resulting precipitates were collected by filtration, washed with cold ethanol and air-dried to give the corresponding pure products. The solvent was evaporated from the filtrate to recover the catalyst, and the catalyst was reused for subsequent reactions. In the initial stages, we explored the best reaction conditions using three-component reaction of benzaldehyde, malononitrile, and dimedone as the model reaction. The effects of catalyst loading, temperature, and solvents were explored for this reaction. It was found that the best results were obtained for the synthesis of 2-amino-4H-chromenes and 2-amino-4H-pyran when the three-component reaction was carried out with equivalent molar quantities of each of the reactants in water containing 10 mol% sodium malonate at 70°C for 15 min in 96% yield. After finding optimal conditions, these conditions apply to other reactants and the target heterocyclic products were obtained with excellent yields. This study describes an efficient, environmentally benign, and clean one-pot, three-component synthesis of 2-amino-4H-chromenes and 2-amino-4H-pyran-3-carboxylates in the presence of sodium malonate as the commercially available catalyst in an aqueous medium at 70°C. High yields, mild reaction conditions, relatively shorter reaction times, use of simple reagents, and no requirement of the ultrasound, microwave, and ball milling techniques are the salient features and benefits of the present method. In addition, the present process is smooth and green.

Synthesis of novel 6-amino-2-(hydroxymethyl)-8-aryl-7-(phenylsulfonyl)pyrano[3,2-b]pyran-4(8H)-one derivatives catalyzed by nano-cellulose-OSO3H

A novel series of 6-amino-2-(hydroxymethyl)-8-aryl-7-(phenylsulfonyl)pyrano[3,2-b]pyran-4(8H)-one derivatives was synthesized via an efficient, mild and rapid protocol. Pyran-annulated heterocycles were obtained in improved yields using aromatic aldehydes, 5-hydroxy-2-hydroxymethyl-4H-pyran-4-one and phenylsulfonylacetonitrile in the presence of nano-cellulose-OSO3H as a suitable and efficient catalyst. Nano-cellulose-OSO3H was synthesized by preparing nano-cellulose as a support, followed by treatment with chlorosulfonic acid (ClSO3H). The proposed protocol represents an eco-friendly approach that provides excellent yields, with mild reaction conditions, ease of workup, survival of different functional groups and short reaction times.

Synthesis of Pyran-Annulated Heterocyclic Systems Catalyzed by Theophylline as a Green and Bio-Based Catalyst

A green synthetic route to the convenient preparation of tetrahydrobenzo[b]pyran, pyrano[2,3-d]pyrimidinone and dihydropyrano[2,3-c]pyrazole scaffolds have been developed using theophylline as a green and bio-based catalyst via tandem Knoevenagel–Michael cyclocondensation reaction in aqueous/ethanol media. All reactions are completed in short period of times and the products are obtained in excellent yields. The salient features of this environmentally friendly approach are green and bio-based catalyst, straightforward work-up with no column chromatographic separation, one-pot procedures, economical and clean synthesis, avoidance of toxic organic solvents and high atom-economy.

K2CO3: A Mild and Efficient Catalyst for the Synthesis of Pyran Annulated Heterocyclic Systems by Grinding Method Under Solvent-Free Conditions

Abstract The potassium carbonate was applied as a green and efficient catalyst for the one-pot synthesis of pyran annulated heterocyclic systems, via the condensation between aromatic aldehydes, malononitrile and dimedone/1-naphtole by a grinding method at room temperature and solvent-free conditions. Short reaction times, environmentally friendly procedure and excellent yields are the main advantages of this procedure which makes it more economic than other environmentally synthetic methods.

An Efficient Eco-Friendly Synthesis of Pyran Annulated Heterocyclic Systems under Conventional Heating and Microwave Irradiation in Solvent-Free Conditions

ABSTRACT1,4-Diazabicyclo[2.2.2]octane (DABCO) has been used as an efficient and reusable solid base catalyst for the rapid and green synthesis of pyran annulated heterocyclic ring systems by the condensation reaction of various activated CH-acids and tetracyanoethylene under conventional heating and microwave irradiation in solvent-free conditions. Excellent yield, very short reaction time (2–5 min), operatinal simplity, easy work-up procedure, avoidance of hazardous or toxic catalysts, and organic solvents are the main advantages of this green methodology which makes it more economic than the other conventional methods.

ChemInform Abstract: Eco‐Friendly, One‐Pot Multicomponent Synthesis of Pyran Annulated Heterocyclic Scaffolds at Room Temperature Using Ammonium or Sodium Formate as Non‐toxic Catalyst.

AbstractThe title compounds (IV), (VI), (VIII), and (X) are obtained by three‐component condensation reaction of aromatic aldehydes, malononitrile, and C—H activated acidic compounds under mild reaction conditions.

Tris-hydroxymethylaminomethane (THAM): a novel organocatalyst for a environmentally benign synthesis of medicinally important tetrahydrobenzo[b]pyrans and pyran-annulated heterocycles

Tris-hydroxymethylaminomethane (THAM): a novel, low cost, green catalyst for the synthesis of medicinally important pyrans and pyran-annulated heterocycles.

Synthesis of pyran annulated heterocyclic scaffolds: a highly convenient protocol using dimethylamine

A facile and rapid three-component synthesis of pharmaceutically diverse pyran annulated heterocycles has been developed via a one-pot condensation of aromatic aldehydes, malononitrile, and different enolizable C–H-activated acidic compounds in the presence of dimethylamine as a newer and effective organo-catalyst in ethanol under mild reaction conditions. Selectivity of various pyran derivatives depends on the structure of enolates. The present protocol has synthetic advantages of excellent yields in much shorter reaction times with no chromatography.

Efficient tandem synthesis of a variety of pyran-annulated heterocycles, 3,4-disubstituted isoxazol-5(4H)-ones, and α,β-unsaturated nitriles catalyzed by potassium hydrogen phthalate in water

A variety of 4H-chromenes, benzochromenes, 4,5-dihydropyrano[3,2-c]chromenes, 4H-pyran-3-carboxylates, and 3,4-disubstituted isoxazol-5(4H)-ones have been synthesized in high yields by using potassium hydrogen phthalate (KHP) as an inexpensive, commercially available catalyst. It was found that the three-component tandem reaction enabled synthesis of pyran-annulated heterocycles in water at 50 °C. 3,4-Disubstituted isoxazol-5(4H)-ones were synthesized by use of 10 mol% KHP in water at room temperature. Also, treatment of methylene-containing compounds (malononitrile or ethyl cyanoacetate) with aromatic aldehydes in the presence of 5 mol% KHP resulted in α,β-unsaturated nitriles. The procedure is an easily performed, straightforward method for synthesis of a variety of pyran-annulated compounds, isoxazol-5(4H)-one-containing heterocycles, and Knoevenagel adducts. The reaction is safe, uses mild conditions, and is environmentally benign. Other notable advantages are reuse of the catalyst, no use of hazardous organic solvents, and ease of work-up.

Eco‐friendly, One‐Pot Multicomponent Synthesis of Pyran Annulated Heterocyclic Scaffolds at Room Temperature Using Ammonium or Sodium Formate as Non‐toxic Catalyst

A simple, facile, and convenient practical method for one‐pot synthesis of pharmaceutically interesting diverse kind of pyran annulated heterocycles such as 4H‐pyrano[3,2‐c]coumarins, 4H‐pyrano[3,2‐c]‐α‐pyrones, 5,6,7,8‐tetrahydro‐5‐oxo‐4H‐chromenes and benzo[h]‐4H‐chromenes in the presence of ammonium or sodium formate as catalyst via three‐component condensation reaction of aromatic aldehydes, malononitrile, and C−H activated acidic compounds in aqueous ethanol has been developed mostly at room temperature. The salient features of the present method are mild reaction conditions, good to excellent yields, high atom economy, environmentally benign, easy isolation of products, no column chromatographic separation and reusability of reaction media.