Showing papers on "Pyran published in 2015"

A green one-pot three-component synthesis of tetrahydrobenzo[b]pyran and 3,4-dihydropyrano[c]chromene derivatives using a Fe3O4@SiO2–imid–PMAn magnetic nanocatalyst under ultrasonic irradiation or reflux conditions

Abstract: An efficient and environmentally benign procedure for the synthesis of tetrahydrobenzo[b]pyran and 3,4-dihydropyrano[c]chromene derivatives has been developed by a one-pot three-component reaction of various aldehydes, malononitrile, and dimedone or hydroxycoumarin in the presence of Fe3O4@SiO2–imid–PMAn nanoparticles as magnetic catalysts under ultrasonic irradiation or reflux conditions in water. This new procedure has notable advantages such as operational simplicity, excellent yields, short reaction time, and absence of any tedious workup or purification. In addition, the excellent catalytic performance in a water medium and the easy preparation, thermal stability and separation of the catalyst make it a good heterogeneous system and a useful alternative to other heterogeneous catalysts. Also, the catalyst can be easily recovered by a magnetic field and reused for eight consecutive reaction cycles without significant loss of activity.

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

Abstract: 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.

Total syntheses of murrayamine E, I, and K.

Abstract: We describe efficient synthetic routes to murrayamine A (mukoenine C), O-methylmurrayamine A, mahanine, O-methylmahanine, and murrayamine D and the first total syntheses of murrayamine E, I, and K. Key steps are a palladium-catalyzed construction of the carbazole framework and an annulation of the pyran ring, which is either catalyzed by phenylboronic acid or promoted by a Lewis acid.

N,2-Dibromo-6-chloro-3,4-dihydro-2H-benzo[e][1,2,4]thiadiazine-7-sulfonamide 1,1-dioxide: an efficient and homogeneous catalyst for one-pot synthesis of 4H-pyran, pyranopyrazole and pyrazolo[1,2-b]phthalazine derivatives under aqueous media

Abstract: N,2-Dibromo-6-chloro-3,4-dihydro-2H-benzo[e][1,2,4]thiadiazine-7-sulfonamide 1,1-dioxide (DCDBTSD) as a highly efficient and homogeneous catalyst was successfully applied for the synthesis of 4H-pyran, pyranopyrazole and pyrazolo[1,2-b]phthalazine derivatives by a one-pot multi-component reaction (MCR) in water. The described method has some advantages such as mild and neutral reaction media, high yields, short reaction times, cleaner and easier reaction profiles and compliance with green chemistry protocols.

Enantioselective Amine-Catalyzed [4 + 2] Annulations of Allene Ketones and 2,3-Dioxopyrrolidine Derivatives: Synthesis of 4H-Pyran Derivatives

Abstract: An efficient cinchona alkaloid-derived amine catalyzed asymmetric [4 + 2] cycloaddition is successfully developed. 4H-Pyran fused pyrrolin-2-one products are readily obtained in moderate to high yields with good enantioselectivites by employing allene ketones and 2,3-dioxopyrrolidine derivatives as substrates.

On water synthesis of pyran–chromenes via a multicomponent reactions catalyzed by fluorescent t-ZrO2 nanoparticles

Abstract: Here, we have demonstrated fluorescent tetragonal ZrO2 nanoparticle (t-ZrO2 NP) catalyzed green one-pot multicomponent protocol for the synthesis of diverse pyran-fused chromene analogues such as 2-aminochromene, dihydropyrano[3,2-c]chromene, and chromeno[4,3-b]chromene derivatives in water. The rate of the reactions and yields of the products increased significantly in water. In addition, t-ZrO2 NPs showed a higher reactivity than monoclinic ZrO2 NPs. The t-ZrO2 NPs were recycled and the gradual decrease in yield of the product using recycled catalyst could possibly be due to the decrease in Zr-content associated with a decrease in the oxygen vacancies which was evident from fluorescence and atomic absorption studies. However, the tetragonal phase of the catalyst remained intact even at the 10th cycle.

Enzymology of Pyran Ring A Formation in Salinomycin Biosynthesis.

Abstract: Tetrahydropyran rings are a common feature of complex polyketide natural products, but much remains to be learned about the enzymology of their formation. The enzyme SalBIII from the salinomycin biosynthetic pathway resembles other polyether epoxide hydrolases/cyclases of the MonB family, but SalBIII plays no role in the conventional cascade of ring opening/closing. Mutation in the salBIII gene gave a metabolite in which ring A is not formed. Using this metabolite in vitro as a substrate analogue, SalBIII has been shown to form pyran ring A. We have determined the X-ray crystal structure of SalBIII, and structure-guided mutagenesis of putative active-site residues has identified Asp38 and Asp104 as an essential catalytic dyad. The demonstrated pyran synthase activity of SalBIII further extends the impressive catalytic versatility of α+β barrel fold proteins.

Nanocatalytic one-pot, four-component synthesis of some new triheterocyclic compounds consisting of pyrazole, pyran, and pyrimidinone rings

Abstract: A new series of triheterocyclic compounds containing pyrazole, pyran, and pyrimidinone rings was synthesized via a one-pot condensation of ethylacetoacetate, hydrazine hydrate, barbituric acid, and aromatic aldehydes in the presence of catalytic amounts of titanium dioxide nanowires. Various functional groups were well tolerated under the optimized reaction conditions.

Using magnetic nanoparticles Fe3O4 as a reusable catalyst for the synthesis of pyran and pyridine derivatives via one-pot multicomponent reaction

Abstract: An atom-economical, efficient and mild protocol is described for the synthesis of 2-amino-3-cyanopyridine and 2-amino-3-cyano-4H-pyran derivatives in the presence of high surface area Fe3O4 as a highly effective heterogeneous catalyst via one-pot multicomponent cyclo-condensation reaction.

ZnI2-Catalyzed Diastereoselective [4 + 2] Cycloadditions of β,γ-Unsaturated α-Ketothioesters with Olefins

Abstract: The potential of β,γ-unsaturated α-ketothioesters participating in hetero-Diels–Alder reaction has remained unexplored. We report herein the first study of a ZnI2-catalyzed highly diastereoselective inverse electron demand hetero-Diels–Alder reaction of β,γ-unsaturated α-ketothioesters with olefins to access highly substituted 3,4-dihydro-2H-pyrans. All the reactions proceed with cis-selectivity in moderate to excellent yields. Under similar reaction conditions, terminal alkynes undergo direct conjugate 1,4-addition to yield δ,e-acetylenic α-ketothioesters. Furthermore, the utility of these cycloadducts has been demonstrated by an NBS-MeOH mediated stereospecific efficient access to fully substituted pyran rings. The product bromoethers undergo E2 elimination with DBU, resulting in substituted 3,6-dihydro-2H-pyrans. In addition, the thioester moiety of the products has been used for further transformations, such as amidations and Fukuyama coupling reactions.

Enantioselective Organocatalyzed Synthesis of 2-Amino-3-cyano-4H-chromene Derivatives

Abstract: The structural motif that results from the fusion of a benzene ring to a heterocyclic pyran ring, known as chromene, is broadly found in nature and it has been reported to be associated with a wide range of biological activity. Moreover, asymmetric organocatalysis is a discipline in expansion that is already recognized as a well-established tool for obtaining enantiomerically enriched compounds. This review covers the particular case of the asymmetric synthesis of 2-amino-3-cyano-4H-chromenes using organocatalysis. Herein, we show the most illustrative examples of the methods developed by diverse research groups, following a classification based on these five different approaches: (1) addition of naphthol compounds to substituted α,α-dicyanoolefins; (2) addition of malononitrile to substituted o-vinylphenols; (3) addition of malononitrile to N-protected o-iminophenols; (4) Michael addition of nucleophiles to 2-iminochromene derivatives; and (5) organocatalyzed formal (4+2) cycloaddition reaction. In most cases, chiral thioureas have been found to be effective catalysts to promote the synthetic processes, and generally a bifunctional mode of action has been envisioned for them. In addition, squaramides and cinchona derivatives have been occasionally used as suitable catalysts for the substrates activation.

Synthesis of Spiro Pyran by using Silica-Bonded N-Propyldiethylenetriamine as Recyclable Basic Catalyst

Abstract: In some natural products isatin and its derivatives used as a precursors due to the wonderful biological characteristics. In the biological research, we can raise the biocidal activity with the entity of two or more various heterocyclic moieties in one molecule. In continuation of our work to develop new catalysts for organic transformations, here we are reported the preparation of spirooxindole derivatives. Basis of our method, using of the isatin reaction and malononitrie. Also, in this method, impressible and recyclable catalysts are silica-bonded N-propyldiethylenetriamine and silica-bonded N-propyl diethylenetriamine sulfamic acid. Result showed that, this method has many advantages like as simple work-up method, clean and facile procedure, and environment friendly circumstance.

Multicomponent Reactions of Acetoacetanilide Derivatives with Aromatic Aldehydes and Cyanomethylene Reagents to Produce 4H-Pyran and 1,4-Dihydropyridine Derivatives with Antitumor Activities

Abstract: The multi-component reaction of either acetoacetanilide derivative 1a or b with any of the aldehyde derivatives 2a-d and malononitrile 3 in the presence of triethylamine as a catalyst gave the 4H-pyran derivatives 4a-g, respectively. Carrying the same reaction but using a catalytic amount of ammonium acetate gave the 1,4-dihydropyridine derivatives 5a-f, respectively. The use of ethyl cyanoacetate instead of malononitrile in the presence of a catalytic amount of triethylamine gave the 4H-pyran derivatives 7a-d, respectively. Compound 4e was used to synthesize 1,4-dihydropyridine 9a-c and arylhydraone 11a-e derivatives were synthesized from 4a and e. The anti-tumor evaluations of the newly synthesized products were tested against six human cancer and normal cell lines. The results showed that compounds 4a, b, f, 5d, f, 9 and 11a-d had optimal cytotoxic effect against cancer cell lines with IC50<550 nM. The toxicity of the most active compounds was further measured against shrimp larvae.

Stereoselective Synthesis of 1-Methyl-3',4',5',6'-tetrahydrospiro[indoline-3,2'-pyran]-2-one Derivatives via Prins Cyclization.

Abstract: A novel spirocyclization has been developed for the construction of functionalized spirooxindole pyran via Lewis acid promoted Prins cyclization. The reaction proceeds through formation of a single diastereoisomer with high stereoselectivity. This approach can be used to construct biologically important substituted spirooxindole as well as fluorinated pyran scaffolds.

Synthesis and Cytotoxic Evaluation of Pyran, Dihydropyridine and Thiophene Derivatives of 3-Acetylcoumarin

Abstract: A series of coumarin analogues bearing 4H-pyran rings 2a-d, 11a-d and 1,4-dihydropyridine rings 3a-d, 12a-d at position 3 were synthesized starting from either 3-acetyl coumarin (1) or the coumarin acetohydrazide derivative 4. Condensation of 3-acetylcoumarin (1) with 2-cyanoacetohydrazide afforded 2-cyano-N'-{1-[2-oxo-2H-chromen-3-yl]ethylidene}acetohydrazide (4). Reaction of compound 4 with elemental sulfur and either malononitrile or ethyl cyanoacetate afforded the thiophene derivatives 8 and 9, respectively. The structures of the newly synthesized compounds were confirmed on the basis of their spectral data and elemental analyses. All synthesized compounds were screened for their in vitro anticancer activity against six human cancer cell lines and normal fibroblasts. Several compounds showed potent inhibition with an IC50 value of ˂870 nM. Compound 3d exhibited equivalent cytotoxic effect as the standard CHS 828 against a breast cancer cell line (IC50 value=18 nM). Normal fibroblast cells (WI38) were affected to a much lesser extent (IC50 value >10000 nM).

A facile and efficient synthesis of tetrahydrobenzo[b]pyrans using lactose as a green catalyst

Abstract: Lactose has been used as a mild, efficient, green, and inexpensive catalyst for the synthesis of tetrahydrobenzo[b]pyran derivatives via a one-pot, three-component condensation between aryl aldehydes, malononitrile, and dimedone in H2O:EtOH at 60 °C. This method offers a considerable number of advantages including short reaction time, high to quantitative yields, low cost, easy accesses, and simple work-up.

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

Abstract: 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.

Stereoselective Synthesis of Hexahydro-1H-spiro[isoquinoline-4,4'-pyran] Scaffolds through an Intramolecular Prins Cascade Process.

Abstract: A novel tandem cyclization strategy has been developed for the synthesis of hexahydro-1H-spiro[isoquinoline-4,4′-pyran] derivatives through the condensation of 3-((benzylamino)methyl)but-3-en-1-ol with aldehydes using BF3·OEt2. The reaction proceeds in a highly stereoselective manner, leading to a single diastereoisomer. This approach is a simple and efficient alternative for the synthesis of pharmacologically important spiroisoquinoline scaffolds.