A new direction in the alkylation of 5‐acetyl‐2‐amino‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile with active methylene reagents

In this paper, we report a new synthesis route to 4H‐pyran derivatives and a plausible reaction mechanism. The interaction of 5‐acetyl‐2‐amino‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile with different active methylene reagents gives rise to the cleavage and subsequent recyclization of the pyran ring to afford the corresponding 4H‐pyran derivatives.     

Recent trends in synthetic strategies using magnetic nanostructures as green catalysts in synthesis of pyran analogues

In recent years, magnetic nanoparticles and nanocomposites play an important role as a nanocatalyst in the creation of a wide range of bioactive heterocycles with extraordinarily high activity and selectivity, low energy consumption, and extended life. Among all heterocycles, many natural products, pharmaceuticals, and bioactive compounds contain pyran scaffolds which have a wide range of uses in biomedical research, industry, and medicine. Additionally, these are also widely used in the synthesis of novel heterocyclic systems as precursors. This study focused on recent advances in the last 5 years in using various magnetic recoverable and recycled nanoparticles and nanocomposites to synthesize pyran derivatives and their pharmacological activity. This article has been classified into three subsections: (i) MNPs-metal nanocomposite catalyzed reactions, (ii) MNPs-organic based nanocomposite catalyzed reactions, and (iii) MNPs-ionic liquid nanocomposite catalyzed reactions and (iv) MNPs-acid based nanocomposite to describe catalytic efficiency of magnetic nanocomposites for the synthesis of pyran derivatives. A comparative study of nanocomposites and different approaches for green synthesis of pyrans by highlighting the advantages and disadvantages along with catalyst recovery and recyclability has been mentioned, which will help scientists to probe and stimulate the study of these scaffolds.     

New chemical access for pyran core embedded derivatives from bisalkenylated 1,3-diketones and 1,3-diketoesters via tandem C-dealkenylation and cyclization

New chemical access has been developed for the synthesis of pyran core embedded derivatives from 1,3-diketones and 1,3-diketoesters, in which the active methylene group of 1,3-diketone or 1,3-diketoester was alkenylated with three equivalents of alkenyl bromides in presence NaH to give bisalkenyl 1,3-diketones or 1,3-diketoesters and the resultant bisalkenyl 1,3-diketones or 1,3-diketoesters were reacted with AlCl₃ at room temperature to furnish pyran core embedded derivatives in good to excellent yields.     

New approach to the synthesis of substituted 7H‐furo[3,2‐b]pyran‐7‐ones based on 5‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one derivatives

A convenient approach to the synthesis of the previously unknown 7H‐furo[3,2‐b]pyran‐7‐ones based on the intramolecular cyclization of carbonyl derivatives of 5‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one has been elaborated. Key intermediates in the synthesis of the target 7H‐furo[3,2‐b]pyran‐7‐ones are 3‐hydroxy‐6‐methyl‐2‐(2‐oxo‐2‐arylethyl)‐4H‐pyran‐4‐ones. They are formed as a result of multicomponent condensation of 5‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one with arylglyoxals and 4‐methoxyaniline.     

Microwave Promoted,Sodium Acetate Catalyzed One Pot Synthesis of Poly Functionalized 4H‐Pyrans

A clean and efficient one pot synthesis of 4H‐pyran derivatives through condensation of aromatic aldehydes, malononitrile and dicarbonyl compounds under microwave irradiation in presence of Sodium acetate as a catalyst is described.     

Multi‐wall carbon nanotube supported Co (II) Schiff base complex: an efficient and highly reusable catalyst for synthesis of 1‐amidoalkyl‐2‐naphthol and tetrahydrobenzo[b]pyran derivatives

An immobilized Co (II) Schiff base complex supported on multi‐wall carbon nanotubes was synthesized and characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy , thermogravimetric analysis and inductively coupled plasma mass spectrometry. It was shown that the supported complex is a facile, eco‐friendly, recyclable, reusable and green catalyst for three‐component condensation of 2‐naphthol and acetamide with various aldehydes for the synthesis of 1‐amidoalkyl‐2‐naphthol derivatives under solvent‐free conditions. Also, in a further study, the catalytic application was studied in the synthesis of tetrahydrobenzo[b ]pyran derivatives via the condensation reaction of malononitrile and dimedone with several aromatic aldehydes. The procedures suggested here for the synthesis of 1‐amidoalkyl‐2‐naphthol and tetrahydrobenzo[b ]pyran derivatives offer several advantages, such as stability, recyclability and eco‐friendliness of the catalyst, simple experimental conditions, short reaction times, high to excellent yields and easy work‐up.     

Green synthesis of tetrahydrobenzo[b]Pyrans by microwave assisted multi-component one-pot reactions in PEG-400

Polyethylene glycol is found to be a nontoxic and recyclable reaction medium for the microwave-assisted, multi-component one-pot reactions of aromatic aldehydes with ethyl-2-cyanoacetate and 1,3-cyclohexanedione or 5,5- dimethyl-1,3-cyclohexanedione in the presence of piperidine. This environmentally friendly microwave protocol offers ease of operation and enables recyclability of reaction medium and synthesis of a variety of substituted tetrahydrobenzo[b]pyran derivatives. It is an efficient, promising, and green synthetic strategy to construct tetrahydrobenzo[b]pyran skeleton.     

Synthesis of chiral oxa- and azacycle-fused anthraquinone derivatives

A convenient protocol for the synthesis of chiral pyran and piperidine ring-fused anthraquinone derivatives has been developed from (R)-2,3-O-cyclohexylidene-glyceraldehyde using sequential applications of enyne metathesis, Diels–Alder reaction and aromatization as key steps.     

Uses of ethyl benzoyl acetate for the synthesis of thiophene,pyran, and pyridine derivatives with antitumor activities

The N-(arly)propanamide derivatives 3a,b were used for a series of heterocyclization reactions to give thiophene, pyran, and pyridine derivatives. Thus, these compounds underwent the Gewald's thiophene synthesis through their reactions with either malononitrile or ethyl cyanoacetate and elemental sulfur to afford compounds 6a-f , respectively. In addition, they were subjected through a series of multicomponent reactions (MCRs) to give pyran and fused derivatives. The reactions of 3a,b with either malononitrile or ethyl cyanoacetate gave pyridine derivatives 14a-d , respectively. The latter compounds afforded arylhydrazone derivatives 15a-m through their reactions with any of the aromatic diazonium salts 15a-c . The antitumor of the synthesized compounds against A549 (nonsmall cell lung cancer), H460 (human lung cancer), HT-29 (human colon cancer), and MKN-45 (human gastric cancer cancer) cancer cell lines together with foretinib as the positive control by a MTT assay was measured, and the results obtained showed that many compounds exhibited high potency against the six cancer cell lines.     

Synthesis of pyran derivatives under ultrasound irradiation using Ni nanoparticles as reusable catalysts in aqueous medium

Ni nanoparticles (NPs)-catalysed synthesis of pyran derivatives was achieved by one-pot three-component reactions of aryl aldehydes/ketone, malononitrile and C–H activated compounds in aqueous medium under ultrasound irradiation. The present approach offer several advantages, such as shorter reaction time, higher yields, and environmental friendliness.     

InCl3-promoted a novel Prins cyclization for the synthesis of hexahydro-1H-furo[3,4-c]pyran derivatives

(2-(4-Methoxyphenyl)-4-methylenetetrahydrofuran-3-yl)methanol reacts smoothly with different aldehydes in the presence of InCl₃ at an ambient temperature to afford a novel series of cis-fused 7a,3,6-trisubstituted hexahydro-1H-furo[3,4-c]pyran derivatives in good yields with high selectivity. This is the first Letter on the synthesis of cis-fused hexahydro-1H-furo[3,4-c]pyran derivatives via the Prins cyclization.     

Two‐Step Novel Synthesis of 2‐Amino‐6‐(1,3‐dioxo‐2,3‐dihydro‐1H‐inden‐2‐yl)‐4,7‐diphenyloxepine‐3‐carbonitrile and 5‐(1,3‐Dioxo‐2,3‐dihydro‐1H‐inden‐2‐yl)‐2‐imino‐6‐phenyl‐2H‐pyran‐3‐carbonitrile

Starting from indan‐1,3‐dione, a novel two‐step synthesis of the oxepine derivatives 5a,b and the pyran derivatives 7 and 8 under very simple reaction conditions is described.     

Sulfur-Functionalized Allyl Anions as Synthetic Building-Blocks

Abstract

Ring-opening of epoxides by functionalized allyl anions 1,7,9 is used in the synthesis of furan and pyran derivatives.     

Synthesis of Naphtho[1,8‐bc]pyran Derivatives and Related Compounds through Hydroxy Group Directed C?H Bond Cleavage under Rhodium Catalysis

The straightforward and efficient synthesis of naphtho[1,8‐bc]pyran derivatives and related polycyclic compounds is achieved by the rhodium‐catalyzed oxidative coupling of 1‐naphthols or other phenolic and alcoholic substrates with alkynes. In these annulation reactions, the hydroxy groups effectively act as the key function for the regioselective C? H bond cleavage.     

An Efficient,Multicomponent, One‐pot Synthesis of Tetra Substituted Pyrans in Water

A new and environmentally benign multi‐component synthesis of tetra substituted 4H‐pyran derivatives is developed via the one‐pot reaction of an aromatic aldehyde, malononitrile, and 1,3‐diketone in the presence of NaOH with water as the solvent at RT. The reaction is efficient and affords excellent yields of the products.     

Stereoselective Total Synthesis of Decytospolides A and B Starting from D‐Mannitol

The stereoselective total synthesis of decytospolides A and B, two naturally occurring pyran derivatives, has been achieved using D ‐mannitol as the starting material. The intramolecular oxa‐Michael reaction has been employed to construct the tetrahydropyran ring of the molecules and Weinreb amide formation to generate their side chain with a keto function.     

Thiourea/proline derivative-catalyzed synthesis of tetrahydrofuran derivatives: a mechanistic view

A thiourea/proline derivative-catalyzed synthesis of linear α-substituted tetrahydrofuran/pyran derivatives starting with lactol substrates is presented. This study demonstrates the utility and potential complications of using (thio)urea/proline cocatalysis as each of these catalysts is necessary to provide the observed reactivity, but a time-dependent decrease in enantioselectivity is observed. New mechanistic insights into (thio)urea/proline cocatalysis are presented.     

Diammonium Hydrogen Phosphate: An Efficient and Versatile Catalyst for the One‐Pot Synthesis of Tetrahydrobenzo[b]pyran Derivatives in Aqueous Media

Diammonium hydrogen phosphate was used as a mild, efficient, neutral, and cheap catalyst for the synthesis of various 4H‐benzo[b]pyran derivatives via a one‐pot, three‐component condensation of aromatic aldehydes, active methylene compounds, and dimedone in aqueous media.     

Diversity‐Oriented Synthesis of Novel 2′‐Aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] Derivatives via a One‐Pot Four‐Component Reaction

A sequential one‐pot four‐component reaction for the efficient synthesis of novel 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] derivatives 5 in the presence of AcONH₄ as a neutral, inexpensive, and dually activating catalyst is described (Scheme 1). The syntheses are achieved by reacting ninhydrin ( 1 ) with benzene‐1,2‐diamines 2 to give indenoquinoxalines, which are trapped in situ by malono derivatives 2 and various α‐methylenecarbonyl compounds 4 through cyclization, providing the multifunctionalized 2′‐aminospiro[11H‐indeno[1,2‐b]quinoxaline‐11,4′‐[4H]pyran] analogs 5 . This chemistry provides an efficient and promising synthetic way of proceeding for the diversity‐oriented construction of the spiro[indenoquinoxalino‐pyran] skeleton.     

Synthèse d'oxaphénalènes substitués en position 2 par un groupement électro-attractif

Up to now, little is known about naphtho[1,8-bc]pyran (oxaphenalene) derivatives, although some of them have been detected in the vegetable kingdom. However, very recently [6], 2-nitronaphtho[1,8-bc]pyran and 6-methoxy-2-nitronaphtho[1,8-bc]pyran proved to be powerful mutagenic agents (the most efficient on mammal cells in culture hitherto known). This fact prompted us to investigate further this class of products by studying compounds bearing an electron-withdrawing group in the 2-position. We report in the present paper that, in certain cases, this synthesis can be achieved by the yet unattempted péri-heterocyclization of 8-hydroxy-1-naphthaldehydes with an halogenated active methylene compound in acetone in the presence of potassium carbonate. Thus, among others, 2-acetyl, 2-benzoyl and (4-methoxybenzoyl)naphtho[1,8-bc]pyrans, as well as the corresponding derivatives bearing a methoxy group in the 6-position have been prepared. Nevertheless, such a condensation according to Rap [1] cannot be carried out in certain cases, particularly with acetonitrile.