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Journal articles on the topic 'Pyran - Synthesis'

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Published: 4 June 2021

Last updated: 9 February 2022

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1

Marchalín, Štefan, Dušan Ilavský, Jaroslav Kováč, and Milan Bruncko. "Synthesis and reactions of 5-acetyl-2-amino-3-cyano-4-(5-X-2-furyl)-6-methyl-4H-pyrans." Collection of Czechoslovak Chemical Communications 55, no. 3 (1990): 718–27. http://dx.doi.org/10.1135/cccc19900718.

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Substituted 2-amino-4-(5-X-2-furyl)-4H-pyrans IIIa-IIIe have been prepared by a cyclization reaction of 5-X-2-furylmethylenepropanedinitriles IIa-IIe with 2,4-pentanedione. In reaction of 3-(5-X-2-furyl)-methylene-2,4-pentanediones Ia-Ie with propanedinitrile the formation of 4H-pyrans IIIa-IIIe is accompanied, depending on the catalyst type, by the formation of 5-X-2-furylmethylenepropanedinitriles IIa-IIe. 2-(4-Methylbenzylideneamino)-4H-pyran (V), 2-formylamino-4H-pyran (VI), and 3H, 5H-pyrano[2,3-d]pyrimidine-4-one (VII) have been synthesized by functional modifications of the amino group in 4H-pyran IIIa. The transformation of 4H-pyran ring into pyridine ring gives - from 4H-pyran IIIa - 5-acetyl-3-cyano-4-(2-furyl)-6-methyl-3,4-dihydro-2(1H)-pyridone (VIII) and 5-acetyl-2-amino-3-cyano-4-(2-furyl)-6-methylpyridine (IX). The structure of synthesized compounds III-IX has been proved by means of IR, UV, and NMR spectra.

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2

Elinson, Michail N., Fedor V. Ryzhkov, Victor A. Korolev, and Mikhail P. Egorov. "Pot, atom and step-economic (PASE) synthesis of medicinally relevant spiro[oxindole-3,4′-pyrano[4,3-b]pyran] scaffold." Heterocyclic Communications 22, no. 1 (2016): 11–15. http://dx.doi.org/10.1515/hc-2015-0232.

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AbstractFast (3 min) pot, atom and step economics (PASE) potassium fluoride catalyzed multicomponent reaction of isatins, malononitrile and 4-hydroxy-6-methyl-2H-pyran-2-one results in efficient formation of substituted spirooxindole-3,4′-pyrano[4,3-b]pyrans in 92–96% yields. The developed ‘on-solvent’ approach to the substituted spirooxindole-3,4′-pyrano[4,3-b]pyrans – the pharmacologically perspective substances with known antiviral, antileishmanial, anticonvulsant and anti-HIV activities – is beneficial from the viewpoint of diversity-oriented large-scale processes and represents fast and environmentally benign synthetic concept for the multicomponent reactions strategy.

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3

Marchalín, Štefan, Františka Pavlíková, and Dušan Ilavský. "Synthesis and spectral properties of pyrrolo[3',4':5,6]-4H-pyrano[2,3-d]pyrimidine derivatives." Collection of Czechoslovak Chemical Communications 54, no. 5 (1989): 1336–45. http://dx.doi.org/10.1135/cccc19891336.

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The starting 2-amino-5-ethoxycarbonyl-6-chloromethyl-4-(2-furyl)-3-cyano-4H-pyran (I) afforded on condensation with triethoxymethane 2-ethoxymethylenamino-4H-pyran II; treatment of the latter with ammonia yielded 2-formamidino-3-cyano-4H-pyran III, which, when heated in dilute ethanol, cyclized to 4-amino-6-ethoxycarbonyl-5-(2-furyl)-7-chloromethyl-4H-pyrano[2,3-d]pyrimidine (IV). Compound IV reacted with alkyl- or arylamines to give substituted 5H,6H,8H-pyrrolo[3',4':5,6]-4H-pyrano[2,3-d]pyrimidines VI, one of which (VIb, R = p-CH3C6H4) was alternatively obtained from 2-formamidino-4H-pyrano derivative III. The structures of new tricyclic heterocycles were corroborated by analysis of the NMR spectral data.

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4

Pandit, Kapil S., Pramod V. Chavan, Uday V. Desai, Makarand A. Kulkarni, and Prakash P. Wadgaonkar. "Tris-hydroxymethylaminomethane (THAM): a novel organocatalyst for a environmentally benign synthesis of medicinally important tetrahydrobenzo[b]pyrans and pyran-annulated heterocycles." New Journal of Chemistry 39, no. 6 (2015): 4452–63. http://dx.doi.org/10.1039/c4nj02346c.

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5

Vlachou, Evangelia-Eirini N., and Konstantinos E. Litinas. "An Overview on Pyranocoumarins: Synthesis and Biological Activities." Current Organic Chemistry 23, no. 24 (2020): 2679–721. http://dx.doi.org/10.2174/1385272823666191025151236.

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Pyrano- and dipyranocoumarins are classes of naturally occurring organic compounds with very interesting biological activities. This review focuses on the synthetic strategies for the synthesis of pyranocoumarins and dipyranocoumarins and the biological properties of those compounds. The synthesis involves the formation of the pyran ring, at first, from a coumarin or the formation of pyranone moiety from an existing pyran. Pyranocoumarins and dipyranocoumarins present anti-HIV, anti-cancer, neuroprotective, antidiabetic, antibacterial, antifungal, anti-inflammatory activities. Especially khellactones and calanolides are usually potent and selective in anti-HIV activity. Decursin and decursinol derivatives are effective as anticancer, neuroprotective, antidiabetic, antibacterial, and antifungal agents.

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6

Ilavský, Dušan, Milan Bruncko, Štefan Marchalín, and Lubomír Zalibera. "Synthesis of New 2-Substituted 4-(2-Furyl)-4H-pyrans." Collection of Czechoslovak Chemical Communications 59, no. 6 (1994): 1458–62. http://dx.doi.org/10.1135/cccc19941458.

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Substituted 2-amino-3-cyano-4H-pyrans represent important precursors in syntheses of condensed heterocycles containing a 4H-pyran nucleus. In the context of studies of reactivity of 2-amino-5-acetyl-4-(5-X-2-furyl)-3-cyano-6-methyl-4H-pyrans we were interested in the possibility of preparing 2-aryl(heteroaryl)methyleneamino-4H-pyrans III.

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7

Brütting, Christian, Arndt Schmidt, Olga Kataeva, and Hans-Joachim Knölker. "First Total Synthesis of 7-Isovaleryloxy-8-methoxygirinimbine." Synthesis 50, no. 13 (2018): 2516–22. http://dx.doi.org/10.1055/s-0037-1609717.

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We describe the first total synthesis of the pyrano[3,2-a]carbazole alkaloid 7-isovaleryloxy-8-methoxygirinimbine, using a palladium(II)-catalyzed double C–H-bond activation for construction of the carbazole framework and a phenylboronic acid catalyzed annulation of the pyran ring as key steps.

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8

Sharma, Himani, and Suman Srivastava. "Anion–cation co-operative catalysis by artificial sweetener saccharine-based ionic liquid for sustainable synthesis of 3,4-dihydropyrano[c]chromenes, 4,5-dihydropyrano[4,3-b]pyran and tetrahydrobenzo[b]pyrans in aqueous medium." RSC Advances 8, no. 68 (2018): 38974–79. http://dx.doi.org/10.1039/c8ra06889e.

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Artificial sweetener saccharine based ionic for sustainable synthesis of 3,4-dihydropyrano[c]chromenes, 4,5-dihydropyrano[4,3-b]pyran and tetrahydrobenzo[b]pyrans in aqueous medium scaffolds through Domino Knoevenagel–Michael reaction.

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9

Mosaddegh, Elaheh, Asadollah Hassankhani, Sadegh Pourahmadi, and Dadkhoda Ghazanfari. "Ball Mill–assisted Preparation of Nano-CaCO3 as a Novel and Green Catalyst–based Eggshell Waste." International Journal of Green Nanotechnology 1 (January 1, 2013): 194308921350716. http://dx.doi.org/10.1177/1943089213507160.

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Ball mill–assisted preparation of nano-bio Calcite (CaCO3) based on avian shell and its application as a novel, biodegradable, and heterogeneous catalyst with high catalytic activity and reusability in the green and high efficient synthesis of pyrano[4,3- b]pyrans via a condensation reaction of different aromatic aldehydes, malononitrile, and 4-hydroxy-6-methyl-2 H-pyran-2-one at 120°C under solvent-free conditions is reported. The reaction proceeds to completion within 5–30 min in 90–98% yield. The nanocatalyst was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), elemental analysis, and laser particle sizer.

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10

Bodhak, Chandan, Ashis Kundu, and Animesh Pramanik. "ZrO2 nanoparticles as a reusable solid dual acid–base catalyst for facile one-pot synthesis of multi-functionalized spirooxindole derivatives under solvent free condition." RSC Advances 5, no. 104 (2015): 85202–13. http://dx.doi.org/10.1039/c5ra16259a.

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A two-step one-pot protocol for the facile synthesis of biologically important spirooxindole derivatives such as spiro[4H-pyran-3,3′-oxindoles] and spiro[indoline-3,4′(1H′)-pyrano-[2,3-c]pyrazol-2-ones has been developed.

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11

He, Haitao, Chaorong Qi, Yanglu Ou та ін. "Base-promoted annulation of α-hydroxy ketones and dimethyl but-2-ynedioate: straightforward access to pyrano[4,3-a]quinolizine-1,4,6(2H)-triones and 2H-pyran-2,5(6H)-diones". Org. Biomol. Chem. 12, № 41 (2014): 8128–31. http://dx.doi.org/10.1039/c4ob01858c.

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A novel direct synthesis of pyrano[4,3-a]quinolizine-1,4,6(2H)-triones and 2H-pyran-2,5(6H)-diones from α-hydroxy ketones and dimethyl but-2-ynedioate via a base-promoted cascade annulation has been developed.

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12

Suresh, Lingala, Y. Poornachandra, S. Kanakaraju, C. Ganesh Kumar, and G. V. P. Chandramouli. "One-pot three-component domino protocol for the synthesis of novel pyrano[2,3-d]pyrimidines as antimicrobial and anti-biofilm agents." Organic & Biomolecular Chemistry 13, no. 26 (2015): 7294–306. http://dx.doi.org/10.1039/c5ob00693g.

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A simple and facile synthesis of a series of novel pyrano[2,3-d]pyrimidines have been achieved successfullyviaone-pot three-component reaction of 2-amino-7-methyl-5-oxo-4-phenyl-4,5-dihydropyrano[4,3-b]pyran-3-carbonitriles, DMF-DMA and arylamines.

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13

Someswarao, B., Rasvan Khan P., B. Jagan Mohan Reddy, Sridhar B., and V. Subba Reddy B. "Tandem Prins-type cyclization for the stereoselective construction of fused polycyclic ring systems." Organic Chemistry Frontiers 5, no. 8 (2018): 1320–24. http://dx.doi.org/10.1039/c7qo01164d.

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A novel strategy has been developed for the synthesis of fused tetrahydrofuro[3,2-c]pyrano[2,3-b]chromene derivatives through the condensation of 2-hydroxybenzaldehydes with 2-(3,4-dihydro-2H-pyran-5-yl)ethan-1-ol in the presence of 20 mol% TMSOTf.

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14

Teimuri-mofrad, Reza, and Fatemeh Abrishami. "An efficient synthesis of carboxaldehyde derivatives of 4H-pyran-4-one." Canadian Journal of Chemistry 85, no. 5 (2007): 352–57. http://dx.doi.org/10.1139/v07-034.

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We developed a general method for the synthesis of various 2-mono- and 2,6-di-carboxaldehyde substituted derivatives of 3,5-diphenyl-4H-pyran-4-one and 4H-pyran-4-one. 3,5-Diphenyl-6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4a), 6-methyl-4-oxo-4H-pyran-2-carboxaldehyde (4b), 3,5-diphenyl-4-oxo-4H-pyran-2,6-dicarboxaldehyde (5a), 4-oxo-4H-pyran-2,6-dicarboxaldehyde (5b), 3,5-diphenyl-6-hydroxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (10a), and 6-hydroxymethyl-4-oxo-4H-pyran-2-carboxaldehyde (10b) were obtained from the corresponding di-, tri-, and tetra-bromo derivatives of 2,6-dimethyl-3,5-diphenyl-4H-pyran-4-one (1a) and 2,6-dimethyl-4H-pyran-4-one (1b) by treatment with silver acetate followed by hydrolysis. Compounds 4a and 4b were also obtained by the oxidation of 10a and 10b with barium manganate.Key words: 4H-pyran-4-one, hydroxymethyl and carboxaldehyde derivatives, acetoxylation, hydrolysis, oxidation.

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15

Leutbecher, Heiko, Sylvia Rieg, Jürgen Conrad, Sabine Mika, Iris Klaiber та Uwe Beifuss. "Synthesis of Phenylsubstituted 2H,5H-Pyrano[ 4,3-b] pyran-5-ones and Related Heterocycles via a Domino Knoevenagel Condensation/ 6π-Electron Electrocyclization of 4-Hydroxy-6-phenyl-2H-pyran-2-one with Cyclic and Acyclic α, β-Unsaturated Aldehydes under Different Conditions Synthesis and Crystal Structure of the High-pressure Iron Borate β-FeB2O4 Synthesis and Crystal Structure of the High-pressure Iron Borate β-FeB2O4 Synthesis and Crystal Structure of the High-pressure Iron Borate β-FeB2O4 Synthesis and Crystal Structure of the High-pressure Iron Borate β-FeB2O4 Synthesis and Crystal Structure of the High-pressure Iron Borate β-FeB2O4". Zeitschrift für Naturforschung B 64, № 8 (2009): 1–10. http://dx.doi.org/10.1515/znb-2009-0801.

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A range of new 7-phenyl-2H,5H-pyrano[4,3-b]pyran-5-ones and related tricyclic heterocycles was prepared in a single step by means of a domino Knoevenagel condensation/6π-electron electrocyclization under different reaction conditions, including thermal and microwave conditions. The influence of several ionic liquids as solvents was also studied

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16

Mukherjee, Prasun, and Asish R. Das. "Facile synthesis of functionalized 6-cyano-2-oxa-7-azabicyclo[4.1.0]hept-3-en-1-yl acetates: a catalyst free approach to access the pyran fused 2-acetoxy-NH-aziridines." RSC Advances 6, no. 1 (2016): 132–39. http://dx.doi.org/10.1039/c5ra24510a.

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17

Knölker, Hans-Joachim, Valerie Lösle, and Olga Kataeva. "First Total Synthesis and Investigation of the X-ray Crystal Structure of the Pyrano[3,2-a]carbazole Alkaloid Clausenalansine A." Synthesis 53, no. 02 (2020): 359–64. http://dx.doi.org/10.1055/s-0040-1706551.

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AbstractWe describe the first total synthesis of the recently discovered pyrano[3,2-a]carbazole alkaloid clausenalansine A. The synthetic strategy for the construction of this formylpyrano[3,2-a]carbazole is based on a sequence of Buchwald–Hartwig coupling, palladium(II)-catalyzed oxidative cyclization, Lewis acid promoted annulation of the pyran ring, and chemoselective oxidation of a methyl to a formyl group.

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18

Shi, Da-Qing, Li-Hui Niu, Xiang-Shan Wang, Qi-Ya Zhuang, and Yong Zhang. "Synthesis of 4H,5H-pyrano[3,2-c]pyrano-5-ones in aqueous media." Journal of Chemical Research 2005, no. 11 (2005): 724–26. http://dx.doi.org/10.3184/030823405774909379.

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The reaction of 4-hydroxy-6-methylpyran-2-one with substituted cinnamonitriles in water in the presence of triethylbenzylammonium chloride (TEBA) provide an efficient route to 2-amino-4-aryl-4H,5H-pyrano[3,2-c]pyran-5-one derivatives. The products were characterised by IR, 1H NMR, elemental analysis and were further confirmed by the X-ray crystal structure analysis.

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19

Abed, Nosrat Mustafa, Nadia Sobhy Ibrahim, and Mohamed Helmy Elnagdi. "Studies on Heterocyclic Enamines: New Synthesis of Pyrano[2,3-b]pyndine, Pyrano[2,3-d]pyrimidine and Pyrano[2,3-c]pyrazole Derivatives." Zeitschrift für Naturforschung B 41, no. 7 (1986): 925–28. http://dx.doi.org/10.1515/znb-1986-0721.

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AbstractA variety of novel pyrano[2,3-d]pyrimidines could be obtained via reaction of ethyl 2-amino- 3-cyano-6-methylpyran-4-carboxylate with a variety of reagents. Evidence for the existance of this pyran derivative as a ring chain tautom er is presented.

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20

Sharma, Sakshi, Goutam Brahmachari, Rajni Kant, and Vivek K. Gupta. "One-pot green synthesis of biologically relevant novel spiro[indolin-2-one-3,4′-pyrano[2,3-c]pyrazoles] and studies on their spectral and X-ray crystallographic behaviors." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 72, no. 3 (2016): 335–43. http://dx.doi.org/10.1107/s2052520616005060.

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Synthesesviagreen route and single-crystal X-ray structural investigations have been carried out for three spiro[indolin-2-one-3,4′-pyrano[2,3-c]pyrazole] derivatives, 6′-amino-2-oxo-3′-propyl-2′H-spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-5′-carbonitrile dimethyl sulfoxide monosolvate (5a), 6′-amino-5-fluoro-2-oxo-3′-propyl-2′H-spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-5′-carbonitrile dimethyl sulfoxide monosolvate (5b) and methyl 6′-amino-5-cyano-1-methyl-2-oxo-3′-propyl-2′H-spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-3′-carboxylate 0.25 hydrate (5c), respectively. Compounds (5a) and (5b) crystallize in the triclinic space group P\bar 1, whereas compound (5c) crystallizes in the monoclinic space groupC2/c. In molecules (5a) and (5b) all the rings are practically flat, while in (5c), the heterocyclic pyran ring adopts a flattened-boat conformation. In (5a) and (5b) the cyanide group is oriented in a (−ap)conformation, while the amino group is oriented in a (+ap)conformation with a pyran ring, but in (5c) both the cyanide and amino groups are oriented in a (−ap) conformation with the pyran ring. In the crystal structure of (5a) and (5b), the molecules are linked by an elaborate system of N—H...O and N—H...N hydrogen bonds to generate a zigzag-like construct. In (5c) molecules are linked by N—H...O hydrogen bonds, thereby generating extended chains. The present communication focuses on the detailed and comparative information about spectral behaviors, single-crystal X-ray crystallographic properties and solid-state supramolecular architectures of these synthesized compounds of potential biological interests.

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21

Azimi, Razieh, Zahra Lasemi, and Ayemeh Bagheri Hashkavayi. "Gold Nanoparticle Functionalized Mesoporous Silica-Chitosan as Efficient and Recyclable Catalyst for the Green One-Pot Synthesis of 4H-pyran Derivatives in Aqueous Medium." Letters in Organic Chemistry 17, no. 4 (2020): 268–80. http://dx.doi.org/10.2174/1570178616666190618113635.

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Gold nanoparticle functionalized mesoporous silica-chitosan (Au NPs/silica-chitosan) as an environmentally benign and heterogeneous nanocatalyst was prepared and its properties were characterized using field emission scanning electron microscopy (FE-SEM) and fourier transform infrared (FT-IR). The catalytic activity of Au NPs/silica-chitosan was studied in the synthesis of biologically important 4H-pyran derivatives. In these reactions, efficient and green syntheses of 4H-pyrans were carried out using isatins or aldehydes, active methylene compounds, and 1,3-dicarbonyl compounds in the presence of a catalytic amount of Au NPs/silica-chitosan in water in excellent yields. Au NPs/silica-chitosan can be recovered easily and reused without any significant loss of the catalytic activity. 4H-pyran derivatives were synthesized using Au NPs/silica-chitosan as catalyst in three component reaction of isatins/aldehydes, active methylene, and 1,3-dicarbonyl compounds in water. Au NPs/Silica-Chitosan was prepared by reaction of aqueous solution of HAuCl4 (1 wt.%) and solution chitosan in deionized water and acetic acid with tetraethyl ortho silicate (TEOS) at 100ºC for 24 h. Gold nanoparticle functionalized mesoporous silica-chitosan was prepared and its catalytic activity was investigated for forming 4H-pyran derivatives. In this study, active methylene and 1,3-dicarbonyl compounds reacted with various isatins and aldehydes which afforded the corresponding spirooxindoles with 88-98% yields. This method includes the environmentally friendly reaction conditions, short reaction time, simple work-up, excellent yield, broad scope of usable substrates, recovery and reusability of heterogeneous catalyst.

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22

Eldin, Sanaa M. "Reactions of Cyanothioacetamide Derivatives with 2-Hydrazinothiazol-4(5H)-one: Synthesis, Cyclization and Biological Evaluation of Several New Annelated Pyran, Thiazole, 1,2,4-Triazole and 1,2,4-Triazine Derivatives." Zeitschrift für Naturforschung B 54, no. 12 (1999): 1589–97. http://dx.doi.org/10.1515/znb-1999-1218.

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The thiocarboxamidocinnamonitriles (2) reacted with 2-hydrazinothiazol-4(5H)-one (3) to afford the corresponding pyrano[2,3-d]thiazoles (6). Compounds 6 were used for the synthesis of several new annelated pyran, thiazole, 1,2,4-triazole and 1,2,4-triazine derivatives via their reactions with chloroacetic acid, ethyl chloroformate, diethyl oxalate and acetylacetone. Structures were established based on elemental and spectral data studies. Some of the newly synthesized heterocyclic derivatives were tested for their antimicrobial activity.

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23

Gharib, Ali, and Manouchehr Jahangir. "Catalytic Synthesis of Pyrano- and Furoquinolines Using Nano Silica Chromic Acid at Room Temperature." Organic Chemistry International 2013 (June 17, 2013): 1–7. http://dx.doi.org/10.1155/2013/693763.

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Nano silica chromic acid (nano-SCA) is found to catalyze efficiently the three component-coupling reactions of aldehydes, amines, and cyclic enol ethers such as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild conditions to afford the corresponding pyrano- and furanoquinolines in excellent yields with high endoselectivity. Interestingly, 2,3-dihydrofuran afforded selectively endoproducts under the similar reaction conditions. Heterogeneous reaction conditions, easy procedure, short reaction time, and high yields are some important advantages of this method.

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24

Al-Sheikh, Ahmed, Masuma Begum, Bian Zhang, et al. "Molecular Diversity via Tetrasubstituted Alkenes Containing a Barbiturate Motif: Synthesis and Biological Activity." Molecules 25, no. 24 (2020): 5868. http://dx.doi.org/10.3390/molecules25245868.

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The synthesis of a molecularly diverse library of tetrasubstituted alkenes containing a barbiturate motif is described. Base-induced condensation of N1-substituted pyrimidine-2,4,6(1H,3H,5H)-triones with 5-(bis(methylthio)methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione gave 3-substituted 5-(methylthio)-2H-pyrano[2,3-d]pyrimidine-2,4,7(1H,3H)-triones (‘pyranopyrimidinones’), regioselectively. A sequence of reactions involving ring-opening of the pyran moiety, displacement of the methylthio group with an amine, re-formation of the pyran ring, and after its final cleavage with an amine, gave tetrasubstituted alkenes (3-amino-3-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)propanamides) with a diversity of substituents. Cleavage of the pyranopyrimidinones with an aniline was facilitated in 2,2,2-trifluoroethanol under microwave irradiation. Compounds were tested against Escherichia coli, Staphylococcus aureus, the yeast Schizosaccharomyces pombe, and the pathogenic fungus Candida albicans. No compounds exhibited activity against E. coli, whilst one compound was weakly active against S. aureus. Three compounds were strongly active against S. pombe, but none was active against C. albicans.

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25

Vázquez, Miguel, Fernando Hernández-Borja, Leticia Contreras, et al. "Synthesis of Novel Hybrid 4H-Pyran-lipoic and 4H-Pyran-azetidine Derivatives." Synthesis 50, no. 05 (2017): 1020–26. http://dx.doi.org/10.1055/s-0036-1591730.

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In this study, a molecular hybridization strategy was used to design and synthesize two novel series of hybrid compounds: 4H-pyran-lipoic and 4H-pyran-azetidine, employing ammonium hydroxide and involving the participation of aldehydes, malononitrile, and compounds derived from β-ketoesters to obtain the products with good yields.

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26

Mohamadpour, Farzaneh, Mojtaba Lashkari, and Nourallah Hazeri. "One-Pot Eco-Safe Saccharin-Catalyzed Procedure for Expedient and Convenient Synthesis of Dihydropyrano[2,3-c]pyrazole, Tetrahydrobenzo[b]pyran and Pyrano[2,3-d]pyrimidinone Scaffolds as a Green and Versatile Catalyst." Indonesian Journal of Chemistry 18, no. 1 (2018): 7. http://dx.doi.org/10.22146/ijc.28450.

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A green and facile saccharin-catalyzed procedure is developed for the one-pot convenient synthesis of dihydropyrano[2,3-c]pyrazole, tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone scaffolds via multi-component tandem Knoevenagel cyclocondensation reaction. This procedure has the chief advantages of green, inexpensive and readily available catalyst, high atom-economy, high to quantitative yields and the reaction procedure is mild and involves facile workup procedure to obtain the desired products in short reaction times.

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27

Hussain, Hidayat, Shahid Aziz, Barbara Schulz, and Karsten Krohn. "Synthesis of a 4H-anthra[1,2-b]pyran Derivative and its Antimicrobial activity." Natural Product Communications 6, no. 6 (2011): 1934578X1100600. http://dx.doi.org/10.1177/1934578x1100600621.

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The five-step synthesis of the new 4 H-anthra[1,2- b]pyran derivative 1 is reported. The key steps in this approach included a Marschalk alkylation of 1,4-dihydroxyanthraquinone followed by a Baker–Venkataraman reaction and then an acid-catalyzed cyclization of ring A to form the 4H-anthra[1,2-b]pyran system. Two compounds, the 4H-anthra[1,2-b]pyran 1 and the anthraquinone derivative 6 were evaluated for antimicrobial activity and showed moderate antialgal, antifungal, and antibacterial activities.

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28

Abo Elsoud, Fatma Ahmed, Mohamed Abd-Elmonem, Mohamed Abo Elsebaa, and Kamal Usef Sadek. "Zn(L-proline)2: An efficient and reusable organocatalyst for the synthesis of polyfunctionally substituted pyrans and 2-amino-4-aryl-8-oxo-4,8-dihydropyrano[3,2-b]pyran derivatives." European Journal of Chemistry 10, no. 2 (2019): 166–70. http://dx.doi.org/10.5155/eurjchem.10.2.166-170.1851.

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Efficient synthesis of non-annulated 2-amino-4H-pyrans and 2-amino-8-oxo-4,8-dihydropyrano[3,2-b]pyran derivatives, which are biologically relevant heterocycles is achieved, utilizing a domino three-component reaction of ethyl acetoacetate or kojic acid with aromatic aldehydes and malononitrile catalyzed by Zn(L-proline)2 as reusable organometallic catalyst. The process exhibits high atom economy, short reaction time, simple work up, high yields and environmentally friendly nature. Excellent yields of the targeted molecules have been obtained.

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29

Diac, Andreea Petronela, Ana-Maria Ţepeş, Albert Soran, et al. "Indenopyrans – synthesis and photoluminescence properties." Beilstein Journal of Organic Chemistry 12 (April 27, 2016): 825–34. http://dx.doi.org/10.3762/bjoc.12.81.

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New indeno[1,2-c]pyran-3-ones bearing different substituents at the pyran moiety were synthesized and their photophysical properties were investigated. In solution all compounds were found to be blue emitters and the trans isomers exhibited significantly higher fluorescence quantum yields (relative to 9,10-diphenylanthracene) as compared to the corresponding cis isomers. The solid-state fluorescence spectra revealed an important red shift of λmax due to intermolecular interactions in the lattice, along with an emission-band broadening, as compared to the solution fluorescence spectra.

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30

Khan, Tabassum, and Zeba N. Siddiqui. "Perchloric acid modified-cellulose: a versatile, novel and biodegradable heterogeneous solid acid catalyst for single-pot synthesis of novel bis-pyran annulated heterocyclic scaffolds under solvent-free conditions." New J. Chem. 38, no. 10 (2014): 4847–58. http://dx.doi.org/10.1039/c4nj00529e.

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An eco-friendly synthesis of novel bis-pyran annulated heterocyclic scaffolds (4a–r) and pyran annulated heterocyclic scaffolds (4s–u) using cellulose-HClO<sub>4</sub>as a biodegradable catalyst is described.

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31

Pratap, Ramendra, Brijesh Kumar, and Vishnu Ji Ram. "Substituent-induced regioselective synthesis of 1,2-teraryls and pyrano[3,4-c]pyran-4,5-diones from 2H-pyran-2-ones." Tetrahedron 62, no. 34 (2006): 8158–63. http://dx.doi.org/10.1016/j.tet.2006.06.007.

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32

Li, Shihang, Aimin Yu, Jianfa Li, and Xiangtai Meng. "Synthesis of Benzothiophene-Fused Pyran Derivatives via Piperidine Promoted Domino Reaction." Heteroatom Chemistry 2019 (May 2, 2019): 1–6. http://dx.doi.org/10.1155/2019/4361410.

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A new domino reaction between thioaurones and malononitrile has been reported. This reaction allows efficient access to benzothiophene-fused pyran derivatives in good yields under mild reaction conditions. The substrate scope is broad; a series of benzothiophene-fused pyran derivatives have been synthesized.

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33

Yang, Wei, Shan Wang, Qian Zhang, Qun Liu, and Xianxiu Xu. "Rh(iii)-catalyzed oxidative C–H bond arylation with hydroquinones: sustainable synthesis of dibenzo[b,d]pyran-6-ones and benzo[d]naphtho[1,2-b]pyran-6-ones." Chemical Communications 51, no. 4 (2015): 661–64. http://dx.doi.org/10.1039/c4cc08260e.

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34

Hou, Fang, Wei Zheng, and Nasser Yousefi. "Design, Characterization and Application of The SCMNPs@PC/VB1-Zn as A Green and Recyclable Biocatalyst for Synthesis of Pyrano[2,3-c]pyrazole and 4H-benzo-[b]-pyran Derivatives." Bulletin of Chemical Reaction Engineering & Catalysis 15, no. 1 (2020): 199–212. http://dx.doi.org/10.9767/bcrec.15.1.6179.199-212.

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Eco-friendly and reusable solid acid catalysts (SCMNPs@PC/VB1-Zn) were identified as one of the most effective basic catalysts for the composition of a pot, three-component pyrano[2,3-c]pyrazoles. Methyl-1-phenyl-1H-pyrazole-5(4H)-one, benzaldehyde and malononitrile in high yield at 80 °C. SCMNPs@ PC/VB1-Zn reports the simple and efficient catalysis of a three-component pot reaction of dimedone, aldehydes, and malononitrile to 4H-benzo-[b]-pyran derivatives. This magnetic nanocatalyst can be recycled more than 6 times without dramatically reducing performance with respect to reaction time and efficiency. Copyright © 2020 BCREC Group. All rights reserved

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35

Srinivas, Avula, Malladi Sunitha, and Sriramoju Shamili. "Synthesis and Biological Evaluation of Novel Pyrane Glycosides." Acta Chimica Slovenica 67, no. 4 (2020): 1061–71. http://dx.doi.org/10.17344/acsi.2019.5752.

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A series of novel (5R)-5-((2S,3S)-3-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3,6-dihydro-2H-pyran-2-yl)-3-(4-fluorophenyl)-2,6-diphenyl-3,3a,5,6-tetrahydro-2H-pyrazolo[3,4-d]thiazoles 11a–g and (5R)-5-((2S,3S)-3-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3,6-dihydro-2H-pyran-2-yl)-3-(4-fluorophenyl)-6-phenyl-3,3a,5,6-tetrahydroisoxazolo[3,4-d]thiazoles 12a–g were synthesized by the reaction of chalcone derivatives of (R,Z)-2-((2S,3S)-3-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3,6-dihydro-2H-pyran-2-yl)-5-(4-fluorobenzylidene)-3-phenylthiazolidin-4-ones 10a–g with phenylhydrazine and hydroxylamine hydrochloride. The chemical structures of newly synthesized compounds were elucidated by IR, NMR, MS and elemental analysis. The compounds 11a–g and 12a–g were evaluated for their antibacterial activity and antifungal activity.

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36

Sil, Diptesh, and Vishnu Ji Ram. "An efficient synthesis of 4H,5H-pyrano[3,4-c]pyran-4,5-diones from a suitably functionalized 2H-pyran-2-one." Tetrahedron Letters 45, no. 44 (2004): 8195–97. http://dx.doi.org/10.1016/j.tetlet.2004.09.045.

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37

Saha, Arijit, Soumen Payra, Archana Asatkar, Ashok Raj Patel, and Subhash Banerjee. "[AcMIM]FeCl4: A Magnetically Separable Organocatalyst for the Clean Synthesis of Tetrahydrobenzo[b]pyran Derivatives." Current Organocatalysis 6, no. 2 (2019): 177–82. http://dx.doi.org/10.2174/2213337206666181126114820.

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Background: Recently, organic synthesis using ionic liquids (ILs) via green approach has attracted considerable attention to address the problem associated with environmental pollution. Magnetization of ILs provides added advantages of separation by external magnet. This can be accomplished by incorporation of high-spin iron(III) in the form of tetrachloro or tetrabromoferrate( III). Thus, synthesis of novel magnetically separable ILs for organic transformations is highly desirable. Results: [AcMIm]FeCl4 ionic liquid showed excellent catalytic activity in the one pot threecomponent synthesis tetrahydrobenzo[b]pyran derivatives at room temperature in excellent yields (94-98 %) within short reaction time (15-20 min.). The ILs were recovered and reused for at least six times with the minimum loss of catalytic activity. Methods: Here, we have demonstrated the excellent catalytic activity of acid functionalized magnetic Ils, [AcMIm]FeCl4 in one-pot multicomponent reactions for the synthesis of biologically important tetrahydrobenzo[b]pyran derivatives. Conclusion: A facile and convenient methodology has been developed for the synthesis of bio-active tetrahydrobenzo[b]pyran derivatives using [AcMIm]FeCl4 ionic liquid as an sufficient and reusable catalyst under environment-benign conditions.

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38

Zarins, Elmars, Janis Jubels, and Valdis Kokars. "Synthesis of Red Luminescent Non Symmetric Styryl-4H-Pyran-4-Ylidene Fragment Containing Derivatives for Organic Light-Emitting Diodes." Advanced Materials Research 222 (April 2011): 271–74. http://dx.doi.org/10.4028/www.scientific.net/amr.222.271.

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New organic glassy non symmetric styryl- derivatives of 2(2,6-substituted-4H-pyran-4-ylidene)-malononitrile, 2(2,6-substituted-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione and 2(2,6-substituted-4H-pyran-4-ylidene)-pyrimidine-2,4,6(1H,3H,5H)-trione were synthesized. They form thin solid amorphous films from volatile organic solvents (DCM and chloroform). Their spectral properties have been studied.

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39

Roudbaraki, Seyyed Jalal, Sadaf Janghorban, and Majid Ghashang. "Green Chemistry Preparation of thiochromeno[4,3-b]pyran and benzo[h]thiazolo[2,3-b]quinazoline Derivatives using HSBM Technique over ZnAl2O4 Nano-Powders." Combinatorial Chemistry & High Throughput Screening 22, no. 6 (2019): 421–27. http://dx.doi.org/10.2174/1386207322666190617164617.

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Aim and Objective: The aim of this paper is to introduce HSBM as a green and environmentally friendly technique for the synthesis of thiochromeno[4,3-b]pyran and benzo[h]thiazolo[2,3-b]quinazoline derivatives over ZnAl2O4 nanopowders as an efficient catalyst. Materials and Methods: ZnAl2O4 nanopowders were synthesized via a co-precipitation of Zn(NO3)2 and Al(NO3)3 salts and were characterized by XRD, FE-SEM, TEM and DLS techniques. The as-prepared ZnAl2O4 nano-powders have been used as a catalyst on the synthesis of pyran nucleus using high-speed ball milling (HSBM) technique. The structure of products was confirmed with NMR analysis. Results: ZnAl2O4 exhibits a cubic crystal structure (Space group: Fd-3m) with the average crystallite size of 41 nm. The average particle size of ZnAl2O4 nano-powders determined by DLS technique is 55 nm. The catalytic activity of nano-powders was examined on the synthesis of 2- amino-4,5-dihydro-4-arylthiochromeno[4,3-b]pyran-3-carbonitriles, (8Z)-2-amino-8-arylidene-4,5, 7,8-tetrahydro-4-arylthiopyrano[4,3-b]pyran-3-carbonitriles, 4-aryl-3,4,5,6-tetrahydrobenzo[h]quinazoline- 2(1H)-thiones and 4-aryl-1,3,4,5-tetrahydro-2H-thiochromeno[4,3-d]pyrimidine-2-thione derivatives. All products were obtained in high yields with short reaction times. Conclusion: ZnAl2O4 nanopowders were prepared via a cost-effective co-precipitation method and showed good potential for the synthesis of 4H-pyran analogous in good yields. The salient advantages of HSBM technique include environmentally friendly with reduced solvents, is a simple technique and has low energy costs.

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40

Karpyak, Natalya, Galyna Marshalok, Yaroslav Kovalskyi, and Maria Fedevych. "Joint obtaining of 2,5-diethyl-3,4-dihydro-2H-pyran-2-methanol and sodium salt of 2,5-diethyl-3,4-dihydro-2H-pyran-2-carboxylic acid via CanniZZaro reaction." Chemistry & Chemical Technology 3, no. 2 (2009): 91–94. http://dx.doi.org/10.23939/chcht03.02.091.

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Kinetic regularities of joint obtaining of 2,5-diethyl-3,4-dihydro-2H-pyran-2-methanol and sodium salt of 2,5-diethyl-3,4-dihydro-2H-pyran-2-carboxylic acid have been investigated. Optimal synthesis conditions have been established and physico-chemical characteristics of the main products have been determined.

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41

Panwar, Rahul, Ranjay Shaw, Amr Elagamy, Chandan Shah, and Ramendra Pratap. "Substituent-Dependent Chemoselective Synthesis of Highly Functionalized Benzo[h]quinolines and 4-Benzylpyrans from 2-Methyl-5-nitro-benzonitrile." SynOpen 02, no. 04 (2018): 0276–84. http://dx.doi.org/10.1055/s-0037-1610665.

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A facile, efficient and atom-economic synthesis of highly substituted benzo[h]qninolines was established by reaction of 2-methyl-5-nitrobenzonitrile with suitably functionalized 2H-pyran-2-ones under basic conditions. We observed that the presence of a thiomethyl group at the C-4 position of pyran provides 6-aryl-4-(2-cyano-4-nitrobenzyl)-2-oxo-2H-pyran-3-carbonitrile exclusively without any trace of benzo[h]quinolines. Depending on the nature of the functional group at C-4 of the pyran ring, different products were achieved. To probe the mechanism, we performed control experiments and isolated 3-(1-amino-7-nitro-3-thiophen-2-yl-naphthalen-2-yl)-3-piperidin-1-yl-acrylonitrile, which, on further treatment with base, provided the benzo[h]quinolines. The structure of one the products was characterized by single-crystal X-ray diffraction.

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42

Bogdanowicz-Szwed, Krystyna, та Aleksandra Pałasz. "Synthesis of 3,4-Dihydro-2H-pyrans by Hetero-Diels-Alder Reactions of Functionalized α,β-Unsaturated Carbonyl Compounds with Styrenes". Zeitschrift für Naturforschung B 56, № 4-5 (2001): 416–22. http://dx.doi.org/10.1515/znb-2001-4-515.

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Abstract Cycloadditions of 3-aryl-2-benzoyl-2-propenenitriles 1a,b to styrene (2a) and its methyl or methoxy-substituted derivatives 2b-d proceed regio- and diastereoselectively yielding cis and trans diastereoisomers of 2,4,6-triaryl-3,4-dihydro-2H-pyran-5-carbonitriles 3 and 4 in 59-72% yield. Cycloadducts cis-3 were the major products. Reaction of 5-(4-nitrobenzylidene)-1,3-dimethylbarbituric acid (5) with styrenes 2a-d afforded diastereoisomeric mixtures of 2H-pyrano[2,3-d]pyrimidine-2,4(3H)-diones cis-6 and trans-7 in 71 - 78% yield.

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43

Zhou, Wei, Qi Huang, Hui Zhang, et al. "Facile Synthesis of 4-Perfluoroalkylated 2H-Pyran-2-ones Bearing Indole Skeleton via a Base-Promoted Cascade Process." Synlett 32, no. 12 (2021): 1197–200. http://dx.doi.org/10.1055/a-1525-3647.

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AbstractA protocol for the synthesis of 4-perfluoroalkylated 2H-pyran-2-ones bearing indole skeleton is reported. This efficient synthesis involves a Et3N-promoted Michael addition/enolization/cyclization cascade process at 40 °C in air, using 3-(1-methyl-1H-indol-3-yl)-3-oxopropanenitriles and methyl perfluoroalk-2-ynoates as the easily available starting materials. Various functionalized 6-(1-methyl-1H-indol-3-yl)-2-oxo-4-(perfluoroalkyl)-2H-pyran-5-carbonitrile derivatives were obtained in 44–99% yield.

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44

Wang, Xiang-Shan, Zhao-Sen Zeng, Yu-Ling Li, Da-Qing Shi, and Shu-Jiang Tu. "One-pot synthesis of pyrano[3,2-c]pyran derivatives catalyzed by KF/Al2O3." Arkivoc 2006, no. 11 (2006): 107–13. http://dx.doi.org/10.3998/ark.5550190.0007.b10.

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45

Kiyani, Hamzeh. "Recent Advances in Three-Component Cyclocondensation of Dimedone with Aldehydes and Malononitrile for Construction of Tetrahydrobenzo[b]pyrans Using Organocatalysts." Current Organic Synthesis 15, no. 8 (2018): 1043–72. http://dx.doi.org/10.2174/1570179415666181031124459.

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Background: The majority of naturally occurring compounds, pharmaceuticals, and drug-candidate molecules possess heterocyclic scaffolds. In this context, tetrahydobenzo[b]pyrans are of considerable importance. In the line with the synthesis of these valuable heterocyclic compounds, the researchers tried to synthesize these molecules using different organocatalysts. The development of new strategies for three-component condensation of dimedone, various aldehydes and malononitrile for construction of tetrahydrobenzo[b]pyrans is of particular interest to organic chemists and pharmacologists. Objective: In this review, three-component catalyzed synthesis of tetrahydrobenzo[b]pyran compounds is introduced, focusing on the developments in the use of organocatalysts. Organocatalytic approaches were investigated for the synthesis of tetrahydrobenzo[b]pyrans. This contribution covers the literature concerning the synthesis of heterocycles referred to, in recent times. Conclusion: This review article is associated with the study of the three-component synthesis of tetrahydrobenzo[b]pyrans using organocatalysts. This review also provides an insight into the importance of these heterocycles. In the vast majority of these reactions, water and water-ethanol system have been used as green solvent media for implementation of them. The use of green solvents, the development of less toxic and promising reagents/catalysts as well as the design of inexpensive and reliable approaches are some of the principles of green chemistry, and most of the methods are benefited from them. Tetrahydrobenzo[b]pyrans and organocatalysts open avenue ofnew horizons. The recyclability of the many of these organocatalysts offers an additional merit for the use of these catalysts in 3-CR of aldehydes, dimedone, and malononitrile reactions.

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46

Bhuva, V. V., V. N. Bhadani, H. D. Purohit, and Dipak M. Purohit. "Synthesis and Antimicrobial Screening of 2"-Amino-4"-[2-(4'-Chlorophenyl)-6-Methyl Imidazo[1, 2-a]Pyridine -3-yl]-6"-Aryl-4"-H-Pyran-3"-Carbonitrile." International Letters of Chemistry, Physics and Astronomy 49 (April 2015): 149–54. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.49.149.

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3-Cyano-4,6-disubstituted 4H-pyrans are endowed with a variety of pharmacodynamic activities Looking to the interesting properties of cyanopyrans, it was considered worthwhile to synthesis some new 2"-amino-4"-[2-(4'-chlorophenyl) -6-methyl imidazo [1,2-a] pyridin-3-yl]-6"-aryl-4"-H-pyran-3"- carbonitrile ( 4a-4l ) have been synthesized. The products have been assayed for their biological activity against Gram +ve, Gram –ve bacteria and fungi. Some of the products showed moderate activity in concentration 50μg/mL. The structures of the products have been elucidated by IR, 1H-NMR, Mass spectral data, elemental analysis and thin layer chromatography.Keywords: Cyanopyrans; antibacterial activity; antifungal activity

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47

Cornforth, J., JE Hawes, and R. Mallaby. "A Stereospecific Synthesis of (±)-Abscisic Acid." Australian Journal of Chemistry 45, no. 1 (1992): 179. http://dx.doi.org/10.1071/ch9920179.

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A convenient separation of (E)- and (Z)-3-methylpent-2-enedioic acids was devised, and it was shown that with acetyl chloride or thionyl chloride the (Z)-acid yields the cyclic anhydride while the (E)-acid forms 6-chloro-4-methylpyran-2-one. The chloropyranone by conventional chemistry gave 4-methyl-6-(2′-oxopropyl)pyran-2-one which condensed with 4-methylpent-3-en-2-one in the presence of pyrrolidine, yielding 4-methyl-6-(2′,6′,6′-trimethyl-4′-oxocyclohex-2′-enyl)pyran-2-one. Oxidation with selenium dioxide or t-butyl chromate then gave 6-(1′-hydroxy-2′,6′,6′-trimethyl-4′-oxotyclohex-2′-enyl)-4-methylpyran-2-one, which on reduction by lithium aluminium hydride and reoxidation afforded (±)-abscisic acid stereospecifically.

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48

Samir, Nermin, Riham F. George, Eman Z. Elrazaz, et al. "Synthesis of some tropane-based compounds targeting colon cancer." Future Medicinal Chemistry 12, no. 23 (2020): 2123–40. http://dx.doi.org/10.4155/fmc-2020-0097.

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Background: In continuation of a previous work concerned with the anticancer activity of some 8-alkyl-2,4-bisarylidene-8-nortropan-3-ones, this work focuses on further modification to the tropane/pyran fused skeleton aiming to obtain improved anticancer activity. Methodology: Reaction of 8-alkyl-2,4-bisarylidene-8-nortropan-3-ones 1–21 with malononitrile under basic conditions afforded tropane/pyran hybrids 22–40 and tropane/pyridine hybrids 41, 42. X-ray crystallography for compounds 22 and 41 as representative examples confirmed their structures. They were tested for their anticancer activity in the HCT116 cell line. Results: Compounds 26 and 33 were the most active compounds with IC50 values of 3.39 and 0.01 μM against HCT116. Moreover, they revealed cyclin-dependent kinase-2 (CDK2) inhibition with IC50 = 104.91 and 49.13 nM, respectively. Furthermore, molecular docking of compounds 26 and 33 in the active site of CDK2 confirmed the obtained results. Conclusion: Tropane/pyran scaffold can be considered as a promising core for anticancer agents acting as CDK2 inhibitors.

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49

Esmaeilpour, Mohsen, Jaber Javidi, Farzaneh Dehghani, and Fatemeh Nowroozi Dodeji. "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." RSC Advances 5, no. 34 (2015): 26625–33. http://dx.doi.org/10.1039/c5ra01021g.

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50

Rachedi, Yahia, Oualid Talhi, Artur Silva, et al. "One-Pot Three-Component Synthesis of Bispyrazole-thiazole-pyran-2-one Heterocyclic Hybrids." Synlett 29, no. 13 (2018): 1776–80. http://dx.doi.org/10.1055/s-0037-1610183.

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A new series of some interesting bispyrazole-thiazole-pyran-2-one heterocyclic hybrids has been efficiently synthesized via a one-pot catalyst-free three-component reaction of α-bromoacetylated pyran-2-one derivatives, thiosemicarbazide, and polysubstituted-1-(1H-pyrazol-4-yl)butane-1,3-diones. This multicomponent procedure has been advantageously applied to prepare a structural diversity of heterocyclic hybrids characterized by extensive 1D and 2D NMR spectroscopic studies.

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