- Highly selective tetrahydropyranylation/dehydropyranylation of alcohols and phenols using porous phenolsulfonic acid-formaldehyde resin catalyst under solvent-free condition
-
An efficient protocol for solvent-free chemoselective tetrahydropyranylation/depyranylation of alcohols and phenols is reported herein using mesoporous Phenolsulfonic Acid Formaldehyde Resins as a heterogeneous acid catalyst. The catalyst successfully performed chemoselective protection and deprotection reactions of a wide range of substrates ranging from primary to secondary and tertiary alcohols and also phenols. The reactions were carried out at ambient temperature under solvent-free condition (SolFC) which resulted in high yields within a very short time. FT-IR, TEM, SEM, EDS and TG-DSC analysis techniques were employed to characterize the synthesized polymeric catalyst. The chemoselective nature of our method was confirmed using 13C DEPT-135 NMR studies. The polymer catalyst was found to be recoverable even after 10th catalytic cycle without much depreciation in its activity. The heterogeneity of the catalyst was verified by hot filtration method. Good yield, energy and cost- effective method, solvent-free protocol, mild reaction conditions, no inert atmosphere, metal-free heterogeneous polymer catalyst and excellent recoverability of the catalyst are notable milestones of the reported protocol.
- Rajkumari, Kalyani,Laskar, Ikbal Bahar,Kumari, Anupama,Kalita, Bandita,Rokhum, Lalthazuala
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- The kinetics and mechanism of the homogeneous, unimolecular gas-phase elimination of 2-(4-substituted-phenoxy)tetrahydro-2H-pyranes
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The gas-phase elimination kinetics of tetrahydropyranyl phenoxy ethers: 2-phenoxytetrahydro-2H-pyran, 2-(4-methoxyphenoxy)tetrahydro-2H-pyran, and 2-(4-tert-butylphenoxy)tetrahydro-2H-pyran were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor toluene. The working temperature and pressure were 330 to 390°C and 25 to 89?Torr, respectively. The reactions yielded DHP and the corresponding 4-substituted phenol. The eliminations are homogeneous, unimolecular, and satisfy a first-order rate law. The Arrhenius equations for decompositions were found as follows: 2-phenoxytetrahydro-2H-pyran log k1 (s?1)?=?(14.18?±?0.21)???(211.6?±?0.4)?kJ?mol?1 (2.303 RT)?1 2-(4-methoxyphenoxy)tetrahydro-2H-pyran log k1 (s?1)?=?(14.11?±?0.18)???(203.6?±?0.3)?kJ?mol?1 (2.303 RT)?1 2-(4-tert-butylphenoxy)tetrahydro-2H-pyran log k1 (s?1)?=?(14.08?±?0.08)???(205.9?±?1.0)?kJ?mol?1 (2.303 RT)?1. The analysis of kinetic and thermodynamic parameters for thermal elimination of 2-(4-substituted-phenoxy)tetrahydro-2H-pyranes suggests that the reaction proceeds via 4-member cyclic transition state. The results obtained confirm a slight increase of rate constant with increasing electron donating ability groups in the phenoxy ring. The pyran hydrogen abstraction by the oxygen of the phenoxy group appears to be the determinant factor in the reaction rate.
- Alvarez-Aular, Alvaro,Cartaya, Loriett,Maldonado, Alexis,Coll, David Santiago,Chuchani, Gabriel
-
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- Cyclopropenium Enhanced Thiourea Catalysis
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An integral part of modern organocatalysis is the development and application of thiourea catalysts. Here, as part of our program aimed at developing cyclopropenium catalysts, the synthesis of a thiourea-cyclopropenium organocatalyst with both cationic hydrogen-bond donor and electrostatic character is reported. The utility of the this thiourea organocatalyst is showcased in pyranylation reactions employing phenols, primary, secondary, and tertiary alcohols under operationally simple and mild reaction conditions for a broad substrate scope. The addition of benzoic acid as a co-catalyst facilitating cooperative Br?nsted acid catalysis was found to be valuable for reactions involving phenols and higher substituted alcohols. Mechanistic investigations, including kinetic and 1H NMR binding studies in conjunction with density function theory calculations, are described that collectively support a Br?nsted acid mode of catalysis.
- Smajlagic, Ivor,Durán, Rocio,Pilkington, Melanie,Dudding, Travis
-
supporting information
p. 13973 - 13980
(2018/11/21)
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- Magnetic nanoparticle-supported DABCO tribromide: A versatile nanocatalyst for the synthesis of quinazolinones and benzimidazoles and protection/deprotection of hydroxyl groups
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1,4-Diazabicyclo[2.2.2]octane tribromide supported on magnetic Fe3O4 nanoparticles (MNPs-DABCO tribromide) as a novel heterogeneous tribromide type compound was found to be an efficient and reusable nanocatalyst for the one-pot synthesis of 2-arylquinazolin-4(3H)-ones and 2-aryl-1H-benzo[d]imidazoles through oxidative cyclization of aldehydes with 2-aminobenzamides and 1,2-phenylenediamine, respectively. Also, MNPs-DABCO tribromide catalyzed trimethylsilylation/tetrahydropyranylation and desilylation/depyranylation of a wide variety of alcohols and phenols through changing the solvent medium at room temperature.
- Rostami, Amin,Pourshiani, Omid,Navasi, Yahya,Darvishi, Neda,Saadati, Shaghayegh
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p. 9033 - 9040
(2017/08/29)
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- Zwitterionic imidazolium salt: An efficient organocatalyst for tetrahydropyranylation of alcohols
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An aprotic imidazole based zwitterionic-salt, 4-(3-methylimidazolium)-butane sulfonate has been found to be an efficient organocatalyst for tetrahydropyranylation by the reaction of 3,4-dihydro-2H-pyran (DHP) and different aliphatic alcohols as well as various phenolic compounds. The notable advantages of the present method are general applicability to various alcohols, clean reaction, production of no hazardous waste, open air reaction conditions and high yields. The catalyst can be reused without the loss of significant catalytic activity.
- Mahato, Sachinta,Chatterjee, Rana,Chakraborty Ghosal, Nirnita,Majee, Adinath
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supporting information
p. 1905 - 1915
(2017/10/07)
-
- Croconamides: A new dual hydrogen bond donating motif for anion recognition and organocatalysis
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We introduce bis-aryl croconamides as a new member in the family of dual hydrogen bonding anion receptors. In this study a series of croconamides are synthesised, and the selectivity for anion binding is investigated (Cl- > Br- > I- in CH2Cl2). The croconamides exhibit different structures in the crystal phase depending on the substituents on the aromatic rings, and furthermore, the crystal structure revealed the presence of tautomers. DFT calculations elucidated the complex structures formed upon addition of anion to the croconamides, confirming the order of association constants towards the halogen anions. The use of croconamides as organocatalysts in a proof-of-concept study is demonstrated in the formation of THP ethers. In addition to this, construction of a Hammet plot further elucidates the mechanism in action on formation of THP ethers.
- Jeppesen, Anne,Nielsen, Bjarne E.,Larsen, Dennis,Akselsen, Olivia M.,S?lling, Theis I.,Brock-Nannestad, Theis,Pittelkow, Michael
-
supporting information
p. 2784 - 2790
(2017/04/03)
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- Thiosemicarbazone organocatalysis: Tetrahydropyranylation and 2-deoxygalactosylation reactions and kinetics-based mechanistic investigation
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The first use of thiosemicarbazone-based organocatalysis was demonstrated on both tetrahydropyranylation and 2-deoxygalactosylation reactions. The organocatalysts were optimised using kinetics-based selection. The best catalyst outperformed previously reported thiourea catalysts for tetrahydropyranylation by 50-fold. Hammett investigations of both the organocatalyst and the substrate indicate an oxyanion hole-like reaction mechanism.
- Larsen, Dennis,Langhorn, Line M.,Akselsen, Olivia M.,Nielsen, Bjarne E.,Pittelkow, Michael
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p. 7978 - 7982
(2017/11/28)
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- Supported N-propylsulfamic acid onto Fe3O4 magnetic nanoparticles as a reusable and efficient nanocatalyst for the protection/deprotection of hydroxyl groups and protection of aldehydes
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N-propylsulfamic acid supported onto Fe3O4 magnetic nanoparticles (MNPs-PSA) as an efficient and magnetically reusable nanocatalyst has been reported for the tetrahydropyranylation/depyranylation of a wide variety of alcohols and phenols by changing the solvent medium. Also, the protection of aldehydes as acylals using Ac2O in the presence of catalytic amount MNPs-PSA in good to high yields at room temperature under solvent-free conditions is described. After completing the reaction, the catalyst was easily separated from the reaction mixture with the assistance of an external magnetic field and reused for several consecutive runs without significant loss of their catalytic efficiency.
- Rostami, Amin,Tahmasbi, Bahman,Abedi, Fatemeh
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p. 3689 - 3701
(2016/04/05)
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- 3,5-Dinitrobenzoic acid catalyzed synthesis of 2,3-unsaturated O- and S-glycosides and tetrahydropyranylation of alcohols and phenols
-
A simple procedure for the synthesis of 2,3-unsaturated glycosides in acetonitrile and tetrahydropyranylation of alcohols and phenols in dichloromethane in the presence of 3,5-dinitrobenzoic acid is described. A variety of alcohols and thiols are reacted with glycals to give the desired products in high yields with high α-selectivity.
- Bodipati, Naganjaneyulu,Palla, Srinivasa Rao,Komera, Venkateshwarlu,Peddinti, Rama Krishna
-
supporting information
p. 6878 - 6881
(2015/02/02)
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- Cobalt-salen complex-catalyzed oxidative generation of alkyl radicals from aldehydes for the preparation of hydroperoxides
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Catalytic generation of alkyl radicals from aldehydes via oxidative deformylation was realized using a cobalt-salen complex with H2O 2. The deformylation was thought to proceed through homolytic cleavage of peroxohemiacetal intermediates to provide even primary alkyl radicals under mild conditions. Variously substituted and functionalized hydroperoxides were obtained from corresponding aldehydes in good yield.
- Watanabe, Eiichi,Kaiho, Atsushi,Kusama, Hiroyuki,Iwasawa, Nobuharu
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supporting information
p. 11744 - 11747
(2013/09/02)
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- Solvent-free NaHSO4-SiO2-catalyzed efficient tetrahydropyranylation of alcohols and phenols
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A simple and efficient tetrahydropyranylation of alcohols and phenols has been developed using NaHSO4-SiO2 (0.5 mol%) as a catalyst under solvent-free conditions to yield corresponding tetrahydropyranyl ethers in excellent yields.
- Kinfe, Henok H.,Mebrahtu, Fanuel M.,Moshapo, Paseka T.
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p. 1237 - 1242
(2013/04/10)
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- Short communication: Catalytic tetrahydropyranylation of phenols and alcohols using vanadium(V)-substituted polyoxomolybdates
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Alcohols and phenols were tetrahydropyranylated in the presence of H 7[PMo8V4O40] in good to excellent yields in acetonitrile and under solventfree reaction conditions. A mild and convenient method for the formation and deprotection of ethers (THP ethers) is described. The formation of THP ethers from the corresponding alcohols was accomplished in the presence of acid-sensitive functional groups.
- Gharib, Ali,Jahangir, Manouchehr
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experimental part
p. 287 - 296
(2012/05/20)
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- Polystyrene-supported GaCl3: A new, highly efficient and recyclable heterogeneous Lewis acid catalyst for tetrahydropyranylation of alcohols and phenols
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A new, simple and highly chemoselective method for tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) in the presence of polystyrene-supported gallium trichloride (PS/GaCl3) as a highly active and reusable heterogeneous Lewis acid catalyst at room temperature is presented.
- Rahmatpour, Ali
-
p. 66 - 71,6
(2012/12/11)
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- Tetrahydropyranylation of alcohols and phenols using polystyrene supported lewis acids as catalysts
-
Polystyrene supported TiCl4 (Ps-TiCl4) and polystyrene supported FeCl3(Ps-FeCl3) were prepared by coordinating Lewis acids with polystyrene. The catalysts were characterized by TGA, BET, SEM, IR and pyridine-adsorbed IR. The loading of Ps-TiCl4 and Ps-FeCl3 were 0.35 and 0.3 mmol·g-1 respectively. Both catalysts were found to be efficient for the tetrahydropyranylation and detetrahydropyranylation of various alcohols and phenols in different solvents. Two catalysts can be recovered and reused for five times with good activity. Polystyrene supported TiCl4 (Ps-TiCl4) and polystyrene supported FeCl3(Ps-FeCl 3) were prepared by coordinating Lewis acids with polystyrene. The catalysts were characterized by TGA, BET, SEM, IR and pyridine-adsorbed IR. The loading of Ps-TiCl4 and Ps-FeCl3 were 0.35 and 0.3 mmol·g-1 respectively. Both catalysts were found to be efficient for the tetrahydropyranylation and detetrahydropyranylation of various alcohols and phenols in different solvents. Two catalysts can be recovered and reused for five times with good activity. Copyright
- Zhang, Yi,Dou, Qianqian,Liu, Yuan,Dai, Liyan,Wang, Xiaozhong,Chen, Yingqi
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p. 2567 - 2572
(2013/01/15)
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- PROCESS FOR SELECTIVELY POLYMERIZING ETHYLENE AND CATALYST THEREFOR
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The present invention generally relates to a process that selectively polymerizes ethylene in the presence of an alpha-olefin, and to a metal-ligand complex (precatalyst) and catalyst useful in such processes, and to related compositions. The present invention also generally relates to ligands and intermediates useful for preparing the metal-ligand complex and to processes of their preparation.
- -
-
Page/Page column
(2013/03/26)
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- Synthesis of sulfonic acid functionalized carbon catalyst from glycerol pitch and its application for tetrahydropyranyl protection/deprotection of alcohols and phenols
-
A novel carbon catalyst with -SO3H, -OH and -COOH functional groups was prepared from glycerol pitch by in situ partial carbonization and sulfonation with sulfuric acid. The activity of the catalyst was investigated through tetrahydropyranylation and dehydropyranylation of a wide variety of alcohols and phenols at room temperature by changing the solvent medium from dichloromethane to methanol. Excellent yields, short reaction times, easy and quick isolation of the products and reusability of the catalyst are the main attractions of this method. The novel carbon catalyst holds great potential in the green chemical processes.
- Prabhavathi Devi,Gangadhar,Siva Kumar,Shiva Shanker,Prasad,Sai Prasad
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experimental part
p. 96 - 100
(2011/10/05)
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- Acid-washed bentonite: A new reagent for the deprotection of tetrahydropyranyl ethers
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Acid-washed (pH 4 and pH 6) bentonite earth cleaves the tetrahydropyranyl ethers to the corresponding alcohols in good yield under mild conditions.
- Poon, Po.S.,Banerjee, Ajoy K.,Bedoya, Liadis,Sanchez, Jennifer,Laya, Manuel S.
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experimental part
p. 477 - 479
(2011/10/18)
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- A highly efficient and ecofriendly procedure for tetrahydropyranylation of alcohols and phenols in the presence of in-situ generated I2 under heterogeneous and neutral conditions
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Molecular iodine generated in situ from Fe(NO3) 3?9H2O/NaI acts as a highly efficient catalyst for tetrahydropyranylation of various alcohols and phenols with 3,4-dihydro-2H-pyran in almost quantitative yields. The reaction occurs rapidly in dichloromethane at room temperature, and use of toxic molecular iodine is avoided.
- Rostami, Amin,Rahmati, Sadegh,Khazaei, Ardeshir
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experimental part
p. 663 - 667
(2010/05/18)
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- Copper p-toluenesulfonate/acetic acid: A recyclable synergistic catalytic system for the tetrahydropyranylation of alcohols and phenols
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Copper p-toluenesulfonate/acetic acid was found to be an efficient, chemoselective synergistic catalytic system, with catalyst loading as low as 0.3 mol% leading to clean, high-yielding tetrahydropyranylation of a variety of alcohols and phenols. By simple phase-separation, copper p-toluenesulfonate can be easily recovered and reused for several times without deterioration in catalytic activity.
- Wang, Min,Song, Zhi-Guo,Jiang, Heng,Gong, Hong
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experimental part
p. 601 - 604
(2009/08/07)
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- Generally applicable organocatalytic tetrahydropyranylation of hydroxy functionalities with very low catalyst loading
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This paper presents the first acid-free, organocatalytic tetrahydropyran and 2-methoxypropene protection of alcohols, phenols, and other ROH derivatives utilizing privileged N,N′-bis[3,5-bis(trifluoromethyl)phenyl]thiourea and a polystyrene-bound analogue. The reactions are broadly applicably (also on preparative scale), in particular, to acid-sensitive substrates such as aldol products, hydroxy esters, acetals, silyl-protected alcohols, and cyanohydrins. The catalytic efficiency is truly remarkably with turnover numbers of 100,000 and turnover frequencies of up to 5700 h-1 at catalyst loadings down to 0.001 mol%. The computationally supported mechanistic interpretation emphasizes the hydrogen bond assisted heterolysis of the alcohol and concomitant preferential stabilization of the oxyanion hole in the transition state. Georg Thieme Verlag Stuttgart.
- Kotke, Mike,Schreiner, Peter R.
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p. 779 - 790
(2008/01/03)
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- Tetrahydropyranylation of alcohols and phenols using the synergistic catalyst system, copper(II) chloride-acetic acid
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Copper(II) chloride-acetic acid was found to be an efficient synergistic catalytic system for the tetraphydropyranylation of various alcohols and phenols in high yields at room temperature in short reaction times. Springer-Verlag 2007.
- Wang, Min,Song, Zhi-Guo,Jiang, Heng,Gong, Hong
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p. 599 - 602
(2008/02/03)
-
- N-Bromosuccinimide (NBS): A mild and efficient catalyst for tetrahydropyranylation of alcohols and phenols under solvent-free conditions
-
Different types of alcohols and phenols are tetrahydropyranylated in the presence of NBS catalyst in good to excellent yields under mild, neutral and solvent-free conditions.
- Khazaei, Ardeshir,Rostami, Amin,Raiatzadeh, Ayeh
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p. 1029 - 1032
(2008/03/11)
-
- Reaction of tetrahydropyranyl ethers with triethylsilyl trifluoromethanesulfonate-2,4,6-collidine combination: Speculation on the intermediate, efficient deprotection, and application to efficient ring-closing metathesis as a tether
-
The reaction of tetrahydropyranyl (THP) ethers with triethylsilyl trifluoromethanesulfonate (TESOTf)-2,4,6-collidine proceeded via collidinium salt intermediates to give the alcohol and 4-triethylsiloxybutanal in good yields. The structure of the intermediate was confirmed by 1HNMR and FAB-MS studies and by trapping it with EtOH. The reaction was applied for mild, efficient, and highly chemoselective deprotection method of THP ethers. The characteristic feature of the reaction is that the reaction conditions are weakly basic. Then, the reaction can proceed without affecting acid-labile protecting groups. Furthermore, the intermediates from alkenol-THP ether were trapped with other alkenols to give acyclic mixed acetals, which were subjected to efficient ring-closing metathesis by using the tetrahydropyranyl unit as a tether.
- Fujioka, Hiromichi,Okitsu, Takashi,Ohnaka, Takuya,Sawama, Yoshinari,Kubo, Ozora,Okamoto, Kazuhisa,Kita, Yasuyuki
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p. 636 - 646
(2008/02/09)
-
- Solvent-free carbon-oxygen bond formation catalysed by CeCl 3·7H2O/NaI: Tetrahydropyranylation of hydroxy groups
-
An efficient and highly chemoselective method fo the protection of free hydroxy compounds with 3,4-dihydro-2H-pyran is reported. Since the deprotection of THP-ethers occurs very readily at room temperature, the successful use of this type of protecting group depends only upon how readily it can be introduced. For this we have examined the tetrahydropyranylation of alcohols and phenols catalysed by the CeCl3·7H2O/NaI system surface under solvent-free conditions. The reaction presents the advantage of being performable under extremely mild conditions by use of catalytic amounts of an interesting Lewis acidic system consisting of the CeCl3· 7H2O/NaI catalyst combination, which can be easily separated from the reaction mixture. The advantages of this procedure, which utilizes cheap and "lfriendly" reagents, over the previously reported ones are discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Bartoli, Giuseppe,Giovannini, Riccardo,Giuliani, Arianna,Marcantoni, Enrico,Massaccesi, Massimo,Melchiorre, Paolo,Paoletti, Melissa,Sambri, Letizia
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p. 1476 - 1482
(2007/10/03)
-
- Silica-gel-supported aluminium chloride: A stable, efficient, selective, and reusable catalyst for tetrahydropyranylation of alcohols and phenols
-
A simple, effective, and highly chemoselective method to form 2-tetrahydropyranyl ethers of alcohols and phenols in the presence of silica-gel-supported aluminium chloride as a heterogeneous Lewis acid catalyst is described. The catalyst can be easily recovered and reused without appreciable change in its efficiency. Copyright Taylor & Francis Group, LLC.
- Borujeni, Kaveh Parvanak
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p. 2705 - 2710
(2007/10/03)
-
- Silica-supported perchloric acid (HClO4-SiO2): A versatile catalyst for tetrahydropyranylation, oxathioacetalization and thioacetalization
-
A simple and convenient synthetic protocol for the protection of hydroxyl group as tetrahydropyranyl ether as well as carbonyl functionality as oxathioacetal and thioacetal has been achieved using a catalytic amount of silica-supported perchloric acid und
- Khan, Abu T.,Parvin, Tasneem,Choudhury, Lokman H.
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p. 2497 - 2502
(2008/02/03)
-
- A mild and efficient tetrahydropyranylation and detetrahydropyranylation of alcohols and phenols by VCl3
-
Vanadium chloride is found to be an efficient catalyst for the tetrahydropyranylation and detetrahydropyranylation of various alcohols and phenols, giving good yields at room temperature and short reaction times. 2005 Springer Science+Business Media, Inc.
- Narsimha Reddy,Sunil Kumar,Kumar,Srinivasulu,Thirupathi Reddy,Rajitha
-
p. 1371 - 1373
(2007/10/03)
-
- A mild and efficient method for tetrahydropyranylation and detetrahydropyranylation of alcohols and phenols by BiOClO4.xH 2O (or) BiONO3
-
A mild and efficient method for the protection of alcohols and phenols as tetrahydropyranyl ethers 3a-k and their deprotection at room temperature using BiOClO4.xH2O (or) BiONO3 as catalyst is described.
- Thirupathi Reddy,Narsimha Reddy,Sunil Kumar,Srinivasulu,Rajitha
-
p. 2396 - 2398
(2007/10/03)
-
- Chemoselective tetrahydropyranylation of alcohols and phenols using polystyrene supported aluminium chloride as a catalyst
-
A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl3. The method is also highly selective for monoprotection of symmetrical diols.
- Tamami, Bahman,Parvanak Borujeny, Kaveh
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p. 715 - 718
(2007/10/03)
-
- A simple and efficient tetrahydropyranylation using N-bromosuccinamide
-
Tetrahydropyranylation of hydroxyl groups of alcohols and phenols has been achieved easily and efficiently using N-bromosuccinamide at room temperature.
- Das, Biswanath,Reddy, M. Ravinder,Ravindranath,Reddy, V. Saidi,Venkateshwarlu
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p. 1711 - 1712
(2007/10/03)
-
- Cupric sulfate pentahydrate (CuSO4·5H2O): A mild and efficient catalyst for tetrahydropyranylation/depyranylation of alcohols and phenols
-
Various alcohols and phenols can be smoothly converted to the corresponding THP ethers using 20 mol % CuSO4·5H2O under mild reaction conditions at room temperature. Some of the major advantages of this procedure are nonaqueous work-up, very good yields, less expensive catalyst and compatibility with other protecting groups.
- Khan, Abu T.,Choudhury, Lokman H.,Ghosh, Subrata
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p. 7891 - 7894
(2007/10/03)
-
- Palladium-catalyzed couplings to nucleophilic heteroarenes: The total synthesis of (-)-frondosin B
-
The total synthesis of (-)-frondosin B, the enantiomer of naturally-occuring (+)-frondosin B, is described, wherein a palladium-catalyzed cyclization is used to establish the tetracyclic ring system of the natural product. Graphical Abstract.
- Hughes, Chambers C.,Trauner, Dirk
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p. 9675 - 9686
(2007/10/03)
-
- Efficient tetrahydropyranylation of phenols and alcohols catalyzed by supported Mo and W Keggin heteropolyacids
-
The protection of phenols as tetrahydropyranyl acetals is studied using supported Keggin heteropolyacids as catalysts, specifically molybdophosphoric or tungstophosphoric acids supported on silica. Phenol tetrahydropyranyl acetals are obtained in short times at room temperature with excellent yields. Protection of alcohols is also performed under mild conditions using both supported heteropolyacids, with yields ranging between good and quantitative. The reactions are clean and their workup is very simple. The use of these solid catalysts allows replacing the usual soluble inorganic acids, contributing to waste reduction.
- Romanelli,Vazquez,Pizzio,Caceres,Blanco,Autino
-
p. 1359 - 1365
(2007/10/03)
-
- Facile Tetrahydropyranylation of Alcohols and Phenols Using Anhydrous Calcium Chloride under Mild and Neutral Conditions
-
Treatment of 3,4-dihydro-2H-pyran with various alcohols and phenols in the presence of a catalytic amount of anhydrous calcium chloride in dichloromethane furnished tetrahydropyranyl ethers under almost neutral conditions.
- Bandgar, Babasaheb P.,Sadavarte, Vaibhav S.,Uppalla, Lavkumar S.,Patil, Suresh V.
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p. 425 - 428
(2007/10/03)
-
- Efficient method for tetrahydropyranylation/depyranylation of phenols and alcohols using a solid acid catalyst with Wells-Dawson structure
-
A simple and efficient procedure to form 2-tetrahydropyranyl acetals of phenols and alcohols is reported. Wells-Dawson heteropolyacid catalyst is used both in bulk form or supported on silica, reaction conditions include room temperature and toluene as solvent. Fast deprotection of THP-acetals can be attained by mere change of the solvent using THF-1% MeOH. In both reactions the supported catalyst is easily recoverable and reusable, and the yields are good to excellent.
- Romanelli, Gustavo P.,Baronetti, Graciela,Thomas, Horacio J.,Autino, Juan C.
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p. 7589 - 7591
(2007/10/03)
-
- A mild and efficient method for tetrahydropyranylation/depyranylation of alcohols and phenols under neutral conditions
-
Alcohols and phenols are tetrahydropyranylated rapidly in high yields in the presence of lithium bromide and dichloromethane at room temperature. Deprotection of these THP ethers can also be effected readily by mere change of the solvent to methanol and refluxing with excess lithium bromide. Due to neutral reaction conditions employed, the method is also compatible with compounds having acid sensitive functional groups.
- Reddy,Reddy,Bhanumathi,Rao
-
p. 4323 - 4328
(2007/10/03)
-
- Solvent free tetrahydropyranylation of alcohols and phenols over sulfuric acid adsorbed on silica gel
-
Alcohols and phenols are tetrahydropyranylated in the presence of sulfuric acid adsorbed on silica gel in high to excellent yields in solvent free conditions and is expedited by microwave irradiation. Addition of methanol performs the complete deprotection.
- Heravi, Majid M.,Ajami, Dariush,Ghassemzadeh, Mitra
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p. 1013 - 1016
(2007/10/03)
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- Solvent free tetrahydropyranylation of phenols and alcohols over zeolites HSZ as reusable catalysts
-
Phenols and alcohols are tetrahydropyranylated in the presence of zeolites HSZ in good to excellent yields and selectivities. Addition of methanol performs the complete deprotection.
- Ballini, Roberto,Bigi, Franca,Carloni, Silvia,Maggi, Raimondo,Sartori, Giovanni
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p. 4169 - 4172
(2007/10/03)
-
- SYNTHESIS OF 2H-1-BENZOPYRANS FROM ARYLLITHIUM AND α,β-UNSATURATED ALDEHYDES
-
The synthesis of 2,2-dialkyl-2H-1-benzopyrans (23), (25), (27), (30), (31) and (29) was performed employing the 1,2-addition reaction of aryllithium salts to cyclocitral, 3-methyl-2-butenal, citral and farnesal respectively.Subsequent deprotection with a
- Cruz-Almanza, Raymundo,Perez-Flores, Francisco,Lemini, Cristina
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p. 759 - 774
(2007/10/02)
-
- The conformational behaviour of 2-aryloxytetrahydropyrans and 2-acetoxytetrahydropyran, and barrier to ring inversion
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The 13C nuclear magnetic resonance data of a series of 2-(4-substituted-phenoxy)tetrahydropyrans at 156 K and in CF2Br2 and CHFCl2 solvents show that the axial preference increases with electron withdrawal in the aryloxy group: from 79 percent (ΔG0E->A = -0.4 kcal mol-1) (4-OCH3) to 90 percent (ΔG0E->A = -0.7 kcal mol-1) (4-NO2) in CF2Br2.The axial preference (anomeric effect) is smaller in the more polar CHFCl2 solvent, as expected, and the substituent effect is smaller also: change in ΔG0E->A from -0.3 (4-OCH3) to -0.5 (4-NO2) kcal mol-1.However, the axial preference of 2-acetoxytetrahydropyran is shown to be smaller than that of 2-phenoxytetrahydropyran in CF2Br2 solvent although the acetoxy group is expexted to be more electronegative than the phenoxy group.Furthermore, the polarity of the solvent has no effect on the conformational equilibrium of 2-acetoxytetrahydropyran.The results are interpreted in terms of both orbital and electrostatic interactions.The ring-inversion barrier of 2-alkoxy and 2-aryloxytetrahydropyrans, determined by the temperature-coalescence method, is lower than that of tetrahydropyran by about 1.5 kcal mol-1.
- Quedraogo, Adama,Lessard, Jean
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p. 474 - 480
(2007/10/02)
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- The Thermal ortho-Substitution of Phenols by Vinyl Ethers
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Pyrolysis of a mixture of phenol and 3,4-dihydro-2H-pyran (6) at 150-180 deg C resulted in the formation of 2-(tetrahydro-2H-pyran-2-yl)phenol (3a) in moderate yield.This selective ortho-substitution reaction has been investigated for a range of phenols and a number of vinyl ethers.While it was found to be a fairly general reaction for phenols, only with the vinyl ether (6) and 2,3-dihydrofuran (28a) was the reaction found to be regioselective.Aluminium phenylate strongly catalyses the reaction of phenol with (6), which proceeded under these conditions at room temperature.An ene-type mechanism is proposed for the reaction.
- Pinhey, John T.,Xuan, Phan Thanh
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- A New, Mild Heterogeneous Catalyst for the Tetrahydropyranylation of Alcohols and Phenols
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The hydrochloride salt of a cross-linked macroreticular poly(4-vinylpyridine) resin in bead form is an effective, yet mild acid catalyst for the tetrahydropyranylation of alcohols (primary, secondary, and tertiary) and phenols.The reaction is carried out in the presence of excess dihydropyran without the formation of troublesome oligomeric pyrans.High yields of the desired ethers are obtained even in reactions with alcohols having steric restrictions or acid sensitive amine functionalities.
- Johnston, Richard D.,Marston, Charles R.,Krieger, Paul E.,Goe, Gerald L.
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p. 393 - 394
(2007/10/02)
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- Syntheses d'aryltetrahydropyrannyl ethers
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L'addition de methoxyphenols 1 sur le dihydropyranne en milieu acide donne des produits C- et/ou O-tetrahydropyrannyles 3 et 4 dont le pourcentage est fonction du nombre de substituants methoxy et de la force du catalyseur acide.Les aryl tetrahydropyranny
- Cottet, Francoise,Cottier, Louis,Descotes, Gerard,Srivastava, Rajendra Mohan
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p. 1481 - 1486
(2007/10/02)
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- Catalysis by Acidic Clay of the Protective Tetrahydropyranylation of Alcohols and Phenols
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The K-10 montmorillonite, a readily available and inexpensive industrial catalyst, cleanly effects the title reaction.
- Hoyer, Susanne,Laszlo, Pierre,Orlovic, Mirko,Polla, Eugenio
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p. 656 - 657
(2007/10/02)
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- MIXED AROMATIC-ALIPHATIC ACETALS; THEIR PREPARATION, (1)H AND (13)C-NMR SPECTRA AND HYDROGENOLYSIS BY ETHEREAL SOLUTION OF CHLOROALANE
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The corresponding p-X-phenylisobutyl acetals of acetaldehyde (I), 2-(p-X-phenoxy)tetrahydropyrans (II), 2-(p-X-phenoxy)tetrahydrofurans (III), and cyclohexyl(p-X-phenyl)acetals of acetaldehyde (IV) were prepared by addition of p-X-substituted phenols to isobutyl vinyl ether, 2,3-dihydro-4H-pyran, 2,3-dihydrofuran, and cyclohexyl vinyl ether, respectively.The structures of acetals I-IV were confirmed by their (1)H and (13)C-NMR spectra.Diastereotopic protons of the methylene and geminal methyl groups are anisochronous in the (1)H-NMR spectra of acetals I. (13)C-NMR spectra of acetals IV demonstrate anisochronous behaviour of cyclohexane ring diastereotopic carbon atoms.The constants ?p+ for several groups calculated using (13)C-NMR spectra are: 1-isobutoxy-1-ethoxy- (-0.58), 2-tetrahydrofuryloxy- (-0.59), and 1-cyclohexyloxy-(1-ethoxy) (-0.57).Experimental relative rate constants of hydrogenolysis of acetals I and II by ethereal solution of chloroalane yield best correlations with ?p+ constants of the substituent X, providing the values ρ= -1.09 for compounds of the series I and II, respectively.The importance of these results for finding the rate determining step of the studied reaction is discussed.
- Dusek, Jiri,Sklenar, Vladimir,Jonas, Jaroslav
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p. 2912 - 2923
(2007/10/02)
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