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This article describes the amalgamated of polyboric acid (PBA) and Aminoethyl-3-Aminopropyltriethoxysilane (AEAPTES) by straightforward extrusion process to produce composite (PBA/AEAPTES). It showed basic nature due to amine functionalities on surface of PBA. The composite is applied for the fabrication of pyran derivatives. These reactions are noteworthy for their large product yields, environmental friendliness, quick reaction times, wide range of substrates and no need of hazardous solvents. Moreover, there is no discernible decrease in activity after four reuses of the catalyst and catalyst separated by simple filtration method without any extraction. The resultant composite is characterized by FT-IR, XRD and SEM analysis. In addition, the synthesized compounds characterized by FT-IR, 1H, & 13C NMR analysis. [ABSTRACT FROM AUTHOR]

A new sustainable heterogeneous catalyst for the effective synthesis of 4H-pyran derivatives under mild reaction conditions was investigated. This heterogeneous catalyst was prepared through the complexation reaction between the naturally obtained chitosan from Callinectes sapidus shells and zinc(II) ions (Zn(II)/Chitosan), and characterized using a variety of techniques, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (IR). The corresponding 4H-pyran derivatives were obtained in good to excellent yields (58–96%) in the presence of Zn(II)/chitosan catalyst using water as solvent at 60°C for only 20 min. The catalyst was easily separated from the reaction mixture by simple filtration, resulting in the desired products with excellent purity. In comparison to numerous other catalyst systems for the synthesis of 4H-pyran derivatives, Zn(II)/chitosan, a new sustainable heterogeneous catalyst, demonstrated remarkable efficacy in an environmentally benign solvent, allowing the desired products to be produced under more environmentally friendly reaction conditions. [ABSTRACT FROM AUTHOR]

Polysubstituted derivatives of pyrans, chromenes, and chromeno[2,3-b]pyridines incorporating a 4,5-dichloroisothiazole or 5-arylisoxazole-3-carbaldehyde fragment in the molecule were synthesized by successive and one-step three-component reactions of 4,5-dichloroisothiazole-3-carbaldehyde and 5-arylisoxazole-3-carbaldehyde with various 1,3-diketones, malononitrile or its dimer. The structure of the target products was proven by X-ray structural analysis. Notably, it was found that the planes of the azole and chromene rings in the molecules of (1,2-azol-3-yl)chromenes are almost perpendicular. Intrinsic antitumor activity and synergistic enhancement of the activity in combination with known cytostatics used in the therapy of oncological diseases were found for some of the synthesized compounds. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis of pentasubstituted 4H-pyran derivatives using N-heterocyclic carbene (NHC) catalysis. The researchers developed a new annulation reaction that allows for the rapid synthesis of these derivatives from readily available starting materials. They tested different substrates and found that both electron-withdrawing and electron-donating groups were tolerated. The researchers also explored the effect of different substituents and successfully conducted the reaction on a larger scale. They proposed a plausible reaction mechanism and concluded that their method could be useful for synthesizing functional molecules containing the 4H-pyran group. [Extracted from the article]

Niobium pentachloride functionalised perlite was prepared via a solid state dispersion technique, which was utilized as an efficient heterogeneous catalyst for the synthesis of pyrans. The immobilisation of NbCl5 over perlite was examined by Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Thermogravimetric analysis (TGA), scanning electron microscope (SEM) with energy dispersive spectra (EDS), and Brunauer, Emmett and Teller (BET) surface area measurements. The wt% of NbCl5-loaded perlite was optimized based on the adequacy with respect to the yield of the pyrans in various solvents. The recyclability of the catalyst was validated in synthesizing pyrans and the results marked its efficiency up to five runs. The efficacy of the NbCl5/perlite catalyst was found to be comparable and better with respect to the other heterogeneous catalysts reported. The structures of pyrans were confirmed by FT-IR, 1H and 13C NMR spectral techniques. The proposed recyclable heterogeneous NbCl5/perlite catalyst simplifies the protocol, and has minimal chemical waste, a lower reaction time and a high-yield. [ABSTRACT FROM AUTHOR]

Electrochemical activation of trialkylstannylmethyl group as an electroauxiliary for carbenium ion generation enables the intramolecular Friedel–Crafts alkylation. Electrochemical activation of stannylmethyl group forms carbenium ion which can be trapped by intramolecular (het)aromatic nucleophiles for the formation of new 6-membered cycles. [ABSTRACT FROM AUTHOR]

Pyrans are one of the most significant skeletons of oxygen-containing heterocyclic molecules, which exhibit a broad spectrum of medicinal applications and are constituents of diverse natural product analogues. Various biological applications of these pyran analogues contributed to the growth advances in these oxygen-containing molecules. Green one-pot methodologies for synthesising these heterocyclic molecules have received significant attention. This review focuses on the recent developments in synthesising pyran ring derivatives using reusable catalysts and emphasises the multicomponent reaction strategies using green protocols. The advantages of the catalysts in terms of yields, reaction conditions, and recyclability are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A direct access to O-heterocycles by Bi(OTf)3-catalyzed intermolecular cyclization of phenols with diols is described. Catalytic dehydrative tandem formation of C–O and C–C bonds was achieved by using a Bi(OTf)3 catalyst without any additives. The catalytic intermolecular cyclization of phenols with various diols proceeded to give the corresponding chromanes in up to 91% yield and/or pyran derivatives in up to 66% yield. [ABSTRACT FROM AUTHOR]

In the present work, the reaction of the acetoactanilide derivatives with either benzenediazonium chloride, 4‐chlorobenzenediazonium chloride, or 4‐methoxybenzenediazonium, gave arylhydrazone derivatives. Heterocyclizations of the latter compounds were carried out to afford new thiophene, pyran and pyridine derivatives. The cyctotoxicity of the synthesized compounds against the selected six cancer cell lines was determined where eleven compounds exhibited the highest inhibitions. Through out this work, the produced pyridazine derivatives were selected for evaluation against cancer cell lines categorized according to the disease and the compounds showed high inhibitions. The results obtained in this work encourage further work in the future. [ABSTRACT FROM AUTHOR]

An efficient procedure between imidazo[1,2-a]pyrimidine-2-carbaldehyde, malononitrile, enolizable C–H activated acidic compounds, and sodium carbonate is described for the synthesis of potential biologically active, novel imidazo[1,2-a]pyrimidine-based pyran analogs through one pot, multicomponent reactions at room temperature. This method provided mild reaction conditions, simple purification without column chromatography, and moderate to good yields for the construction of imidazo[1,2-a]pyrimidine-based pyran derivatives. The structures of target compounds were established with different spectroscopic analyses. [ABSTRACT FROM AUTHOR]

Cyclic diaryl ethers are present in multiple natural compounds, organic pollutants as well as in π-conjugated organic molecular materials. This short review aims at overviewing the main synthetic advances in the O-annulation methods for preparing five-, six-, and seven-membered rings through C–H cleavage. 1 Introduction 2 Five-Membered Rings: The Dibenzofuran (DBF) Motif 2.1 Palladium-Catalysed C–H Activation 2.2 Copper-Catalysed C–H Activation 2.3 Non-CH Activation Oxidant-Mediated Cyclisation 2.4 Light-Mediated Cyclisation 2.5 Acid-catalysed C–O Cleavage/C–O Formation 3 Six-Membered Rings: DBX, PXX, Xanthone, and Their Derivatives 3.1 Dibenzoxanthene (DBX) 3.2 Peri -Xanthenoxanthene (PXX) 3.3 Xanthones 3.4 Miscellaneous 4 Seven-Membered Rings: Cularine 5 Conclusion [ABSTRACT FROM AUTHOR]

An eco-friendly synthesis of pyrano[3,2-c]chromen-5(4H)-one derivatives was conducted by the condensation of 4-hydroxycoumarins, aromatic aldehydes, and acetophenones. Clean profile, excellent yield, ambient temperature, and use of visible light intensity instead of catalyst are the attractive features of this method. [ABSTRACT FROM AUTHOR]

1,4-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. [ABSTRACT FROM AUTHOR]

A high-yielding, practical, efficient, and environmentally benign one-pot multicomponent synthesis of functionalized 2-amino-4Hpyrans from β-dicarbonyl compounds, malononitrile, and aldehydes is presented. Good to excellent yields were obtained under mild reaction condition and with short reaction times by using magnetite-supported graphitic carbon nitride as a truly recyclable catalyst. This efficient and simple technique avoids the use of solvent extraction and column chromatography. In addition, the catalyst can be easily and effectively recovered and reused several times without significant loss of its catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: Convergent total synthesis of bryostatin 8 has been accomplished by an organosilane‐based strategy. The C ring is constructed stereoselectively through a geminal bis(silane)‐based [1,5]‐Brook rearrangement, and the B ring through geminal bis(silane)‐based Prins cyclization, thus efficiently joining the northern and southern parts of the molecule. [ABSTRACT FROM AUTHOR]

The study of the regioselectivity of insertion of unsymmetrical alkynes into the carbon-carbon bond of oxetan-3-one in the presence of a nickel catalyst has revealed a strong directing effect of a 2-thienyl substituent. This effect is larger than those of 2-vinylbenzene, trimethylsilyl, aryl, or 3-thienyl groups. [ABSTRACT FROM AUTHOR]

An iron-catalyzed cyclization of 1,6-enones with aldehydes was developed. With this method, a variety of poly-functionalized 3,4-dihydro- 2H-pyrans were prepared efficiently and selectively. The 6-endo-trig radical cyclization onto the keto oxygen is the key step of this transformation. [ABSTRACT FROM AUTHOR]

A simple and versatile one-pot three-component synthetic protocol is devised for heterocycles, viz. 2,6-diamino-4-substituted-4H-pyran-3,5-dicarbonitrile derivatives, in short reaction times ( $$\approx $$ 30 min) at room temperature using ethanol as a solvent. This method involves the three-component reaction of malononitrile, substituted aldehydes, and cyanoacetamide catalyzed by chitosan-doped calcium hydroxyapatites (CS/CaHAps) giving good to excellent yields (86-96%). Twelve new pyran derivatives ( 4a- l) were synthesized and their structures were established and confirmed by different spectroscopic methods ( $$^{1}$$ H NMR, $$^{13}$$ C NMR, $$^{15}$$ N NMR, and HRMS). The heterogeneous catalyst, CS/CaHAp, was characterized by various instrumental techniques including XRD, TEM, SEM, and FT-IR and TGA spectroscopies. The catalyst was easily separable and reusable for up to six runs without any apparent loss of activity. The reported protocol has many benefits, such as ease of preparation, use of a green solvent, reduced reaction times, excellent product yields, and operational simplicity. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Pyrans are privileged heterocyclic structures found in numerous natural compounds with extraordinary biological activities. The synthesis of these relevant structures has attracted a great deal of attention over the years. Catalytic methodologies based on the activation of neutral unsaturated functionalities of acyclic compounds that undergo intramolecular cyclizations have achieved prominent synthetic relevance. In this short review, we discuss the successful construction of di- hydropyran and dihydro-1,4-oxazine derivatives from acyclic precursors by metal-catalyzed intramolecular cyclizations through carbon--carbon, carbon--oxygen, and carbon--nitrogen bond formation. Remarkable synthetic applications are highlighted. 1 Introduction 2 3,4-Dihydropyrans 3 3,4-Dihydro-1,4-oxazines 4 3,6-Dihydropyrans 5 Synthetic Applications 6 Summary [ABSTRACT FROM AUTHOR]

A high-yielding, one-pot, three-component synthesis of functionalized 2-amino-4H-pyrans from β-dicarbonyl compounds, activated cyanomethylene compounds, and aldehydes, mediated by potassium-exchanged zirconium hydrogen phosphate [α-Zr(KPO4)2], is reported. The protocol shows excellent versatility, as it can be applied to aromatic, aliphatic, or α, β-unsaturated aldehydes under solvent-free conditions. [ABSTRACT FROM AUTHOR]

Metal-acid bifunctional catalysts consisting of an acidic silica-alumina support and a hydrogenating metal (nickel, copper, platinum, palladium, or ruthenium), were tested for their ability to modify the selectivity of the 1,2,6-hexanetriol dehydration reaction in the gas phase. The selectivity was found to be controlled by metal type and loading, with the highest observed selectivity to linear α,ω-dioxygenates occurring with a low loading of platinum or copper on silica-alumina and with the highest selectivity to pyrans observed over a nickel on silica-alumina catalyst. The observed selectivity changes were found to be due to parallel reactions leading to the formation of either linear α,ω-dioxygenates or pyran rings and not ring-opening of pyrans to α,ω-dioxygenates suggesting that the metals influenced the interaction of the polyol with the catalyst surface. The introduction of metals also enhanced activity and diminished catalyst deactivation. These results demonstrate that addition of metals to acid catalysts can have significant impact on the dehydration reaction both in terms of selectivity and activity. [ABSTRACT FROM AUTHOR]

An efficient highly diastereo- and enantioselective protocol to access optically pure fluorinecontaining 2-amino-cyclopenta[b]pyran derivatives using Lewis acid catalysis and organocatalysis sequence has been developed. The corresponding products could be obtained in good to excellent yields with good to excellent diastereoselectivity and enantioselectivity (up to 99:1 dr, >99% ee). [ABSTRACT FROM AUTHOR]

A series of 4-aryl/heteroaryl-4 H-fused pyrans was synthesized via multicomponent reaction in a microwave synthesizer. All the pyrans were evaluated for in vitro xanthine oxidase inhibition. Structure-activity relationship was also established. Among the series of 108 compounds, Compound 5n was the most potent displaying remarkable inhibition against the enzyme with an IC value of 0.59 μM. Enzyme kinetic study was carried out for the compound 5n to determine the type of inhibition. The study revealed that the compound 5n was a mixed-type inhibitor. Molecular modelling studies were also performed to figure out the interactions of both the enantiomers of 5n with the amino acid residues of the enzyme. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The article describes the synthesis of heterocyclic compounds based on reactive aryl trichloroallyl ketones, 1-aryl-3,4,4-trichloro-3-buten-1-ones. It states that the interaction between 1-aryl-3,4,4-trichloro-3-buten-1-ones with guanidine in ethanol led to the formation of 2,3,4,6-substituted 4?-pyran derivatives, aryl(6-aryl-2-dichloromethyl-4-dichloromethylene-4?-pyran-3-yl)methanones. The authors also performed X-ray structural analysis of derivative of pyran.

A small library of 30 thiomarinol analogues was successfully synthesised using as a key step-a catalytic enantioselective tandem oxa[4+2] cycloaddition/aldehyde allylboration methodology. With this method, highly substituted $$\alpha $$ -hydroxyalkyl dihydropyrans were assembled in a single three-component reaction utilizing three different enol ethers and a wide variety of aldehydes, such as aromatic, heteroaromatic, unsaturated and aliphatic aldehydes. In a second operation, a mild and direct method for reducing an acetal unit in the $$\alpha $$ -hydroxyalkyl dihydropyrans was optimised without the need for protecting a nearby hydroxyl group. This procedure facilitated the synthetic sequence, which was completed by a dihydroxylation of the residual olefin of $$\alpha $$ -hydroxyalkyl 2 $$H$$ -pyrans to provide the desired library of dihydroxylated pyran analogues reminiscent of the thiomarinol antibiotics. The relative stereochemistry of the resulting library compounds was demonstrated by X-ray crystallography on one of the analogues. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Antiproliferative and antimicrobial activity of methyl-6-amino-3-acyl-4-aryl-5-cyano-4 H-pyran-2-carboxylates and their analogs that were synthesized from methyl-2,4-dioxobutanoates was studied. Studies of their antiproliferative activity at the USA National Cancer Institute under the program NCI 60 Cell One-Dose Screen found that methyl-6-amino-5-cyano-4-(furan-2-yl)-3-(3-methoxybenzoyl)-4 H-pyran-2-carboxylate had the highest activity, greater than those of busulfan and cisplatin. Methyl-6-amino-3-acetyl-4-phenyl-5-cyano-4 H-pyran-2-carboxylate had antimicrobial activity that was comparable with that of chloramine. [ABSTRACT FROM AUTHOR]

This work has been carried out to explore the reaction of 2-cyanoacetohydrazide with cyclohexanone to form 4,5,6,7-tetrahydroindole derivatives. 2-Hydroxy-4,5,6,7-tetrahydro-1 H-indole-3-carbonitrile was used as the starting material for a series of novel heterocyclic products containing fused oxazine, pyran, pyrazole, pyridazine, and thiophene rings. The antitumor activity evaluation of the newly synthesized compounds against three human tumor cells lines, breast adenocarcinoma (MCF-7), non-small cell lung cancer (NCI-H460), and CNS cancer (SF-268), and with normal fibroblast cells (WI 38) showed that some of these compounds exhibit much higher inhibitory effects towards the three tumor cell lines than the reference drug doxorubicin while being minimally active towards normal cells. [ABSTRACT FROM AUTHOR]

The iodine-catalyzed Prins cyclization of homoallylic alcohols and aldehydes was investigated under metal-free conditions and without additives. Anhydrous conditions and inert atmosphere are not required. The reaction of 2-(3,4-dihydronaphthalen-1-yl)propan-1-ol and 21 aldehydes (aliphatic and aromatic) in CH2Cl2 in the presence of 5 mol % of iodine gave 1,4,5,6-tetrahydro-2H-benzo[f]isochromenes in 54%-86% yield. Under similar conditions, the Prins cyclization of six alcohols containing an endocyclic double bond (primary, secondary, or tertiary) led to dihydropyrans in 52%-91% yield. The acyclic homoallylic alcohols gave 4-iodo-tetrahydropyran in 29%-41% yield in the presence of 50 mol % of iodine. This type of substrate is the main limitation of the methodology. The relative configuration of the products was assigned by NMR and X-ray analysis. The mechanism and the ratio of the products are discussed, based on DFT calculations. [ABSTRACT FROM AUTHOR]

An efficient and concise synthesis of nine populene D analogues was performed using an iodine-catalyzed Prins cyclization as the key transformation. The antiproliferative activity of these new pyrans against several cancer cell lines was then investigated. Among them, an isochromene with moderate activity (mean logGI50 = 0.91) was found. Additionally, compounds with selectivity toward the tumor cell lines NCI-ADR/RES, OVCAR-3, and HT29 were discovered. [ABSTRACT FROM AUTHOR]

A new tetrahydropyran scaffold has been efficiently prepared by Prins reaction between hepta-1,6-dien-4-ol and benzaldehyde. Subsequent functionalizations were further achieved by Mitsunobu reaction and/or by the way of cross-metathesis/Wacker oxidation sequence to deliver diospongin A analogues. [ABSTRACT FROM AUTHOR]

An efficient and straightforward stereoselective synthesis of (6S)-6-[(2R)-2-hydroxy-6-phenylhexyl]-5,6-dihydro-2H-pyran- 2-one is described. The chiral centers were generated by Sharpless asymmetric epoxidation followed by regioselective epoxide ring opening with Red-Al to afford 1,3-diols, exclusively. All the reactions were very clean and the products were obtained in very good yields. [ABSTRACT FROM AUTHOR]

A selective method for 2-aryl-2H- and 4-aryl-4H-3,5-diformylpyrans synthesis from 1,1,3,3-tetramethoxypropane and aromatic aldehydes was developed using an FeCl3 catalyst in MeOH-AcOH and an AlCl3 catalyst in DMA-AcOH. [ABSTRACT FROM AUTHOR]

A number of new 2,6-didisubstituted pyrimidine, pyrazoline, and pyran derivatives were synthesized starting from their chalcone derivative. The synthesized compounds displayed different degrees of antimicrobial activity against Bscillus subtilis (Gram-positive), Pseudomonas aeruginosa (Gram-negative), and Streptomyces species (Actinomycetes). [ABSTRACT FROM AUTHOR]

The present work is dedicated to the 70th anniversary of the Institute of Organic Chemistry, National Academy of Sciences of Ukraine. It contains a review of achievements in the chemistry of heterocyclic compounds, a brief historical account, and information on the work of the Institute’s team in recent years. [ABSTRACT FROM AUTHOR]

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. [ABSTRACT FROM AUTHOR]

An isocyanide-catalyzed reaction between tetracyanoethylene and various activated CH-acid compounds to afford the corresponding pyran annulated heterocyclic ring systems, in high yield at room temperature within a few minutes, is described. To the best of our knowledge, this is the first example in which isocyanide functions as only a catalyst but not a reagent. [ABSTRACT FROM AUTHOR]

Starting from easily available enantiopure pyran derivatives we prepared bicyclic γ-lactam 6, azide 10, and alkyne 18 using simple procedures. These compounds were crucial intermediates for the synthesis of γ-amino acid 8 and dipeptide 9 as well as �triazoles 13, 14, and 19, all containing a carbohydrate-mimicking aminopyran moiety. The generation of triazoles was particularly �efficient by use of a recently reported modification of the click �reaction. [ABSTRACT FROM AUTHOR]

A remarkably efficient double-crossed aldol condensation of tetrahydropyran-4-one with a variety of aromatic aldehydes is described at room temperature in the presence of (trimethylsilyl)diethylamine and lithium perchlorate under solvent-free conditions. Excellent yields of 3,5-bis(arylmethylidene)pyranones are achieved in a facile one-pot general procedure. [ABSTRACT FROM AUTHOR]

The addition of polyhalides to multiple bonds in the synthesis of various heterocyclic compounds is discussed. [ABSTRACT FROM AUTHOR]

Literature and characteristic experimental data correlated in the review concern the intramolecular cyclization by various means of substituted 1,5-diketones of the acyclic, semi-, and bicyclic series, proceeding to the formation of oxygen-containing heterocycles, such as pyrans, pyrylium salts, di- and tetrahydrofurans, and their condensed analogs, aroylfurans etc. [ABSTRACT FROM AUTHOR]

A one-pot synthesis of 4-alkyl-2-amino-4 H-chromene derivatives by base-initiated reactions of aliphatic aldehydes, malononitrile, and resorcinol in water is described. [ABSTRACT FROM AUTHOR]

The analogy goes further: Following the often‐studied donor–acceptor‐substituted cyclopropanes, the corresponding cyclobutane derivatives were employed for the ring‐strain‐driven stereoselective syntheses of carbo‐ and heterocycles. [ABSTRACT FROM AUTHOR]