- Palladium Complexes of Thio/Seleno-Ether Containing N-Heterocyclic Carbenes: Efficient and Reusable Catalyst for Regioselective C-H Bond Arylation
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The synthesis of the novel S,CNHC type half-pincer ligand precursors (L1 and L2) is described herein by using the atom economy reactions of 1-(2-(phenylthio)ethyl)-1H-imidazole with benzyl bromide and bromodiphenylmethane, respectively. The analogous reaction of 1-(2-(phenylselanyl)ethyl)-1H-imidazole with 2-bromoethyl phenyl sulfide has also resulted in a imidazolium bromide (L3) which is a precursor of novel S,CNHC,Se type pincer ligand. The route of silver-NHC transmetalation was employed to get the palladium complexes [Pd(L1/L2–HBr)Cl2] (C1 and C2) and [Pd(L3–HBr)Cl]BF4 (C3). The imidazolium bromide (L1–L3) and palladium complexes (C1–C3) were characterized by using multinuclear NMR and HR-MS. The structure and bonding in the complexes C1 and C2 were validated by X-ray crystallography. Thermally robust and moisture/air insensitive palladium complexes C1–C3 have been explored in the catalysis of C–H bond arylation of imidazoles. The protocol operates under mild reaction conditions in air with an excellent regioselective C–H bond arylation at C-5 position in imidazoles. All the complexes were found to be efficient (yield up to 97 % in 12 h) in the catalysis; however, the activating pincer ligand framework containing Pd catalyst C3, was found to be utmost effective among the three catalysts. Only 0.5 mol-% catalyst loading is required to achieve admirable yield of the desired cross-coupled products. A wide range of substrates was examined, and the developed protocol was applicable to all derivatives with high functional group tolerance and greater efficiency. More importantly, the catalyst C3 has also been found recyclable up to five cycles with minor decrease in efficiency which is highly desirable feature for the development of economical and sustainable industrial reaction processes. The PPh3 and Hg poisoning tests have established the complete homogeneous nature of the catalysis.
- Bhatt, Ramprasad,Bhuvanesh, Nattamai,Sharma, Kamal Nayan,Joshi, Hemant
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- Regioselective C-H arylation of imidazoles employing macrocyclic palladium(II) complex of organoselenium ligand
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In this report we have presented synthesis of a new air stable bidentate selenium ligand (L1) by the reaction of 1,8-bis(2-(chloromethyl)phenoxy)octane with sodium salt of diphenyl diselenide. The reaction of bidentate selenium ligand (L1) with Pd(CH
- Gadwal, Jitendra,Joshi, Hemant,Kumar, Sunil,Makar, Parvesh,Singh, Sohan
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- Palladium-Based Catalysts Supported by Unsymmetrical XYC–1 Type Pincer Ligands: C5 Arylation of Imidazoles and Synthesis of Octinoxate Utilizing the Mizoroki–Heck Reaction
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A series of new unsymmetrical (XYC–1 type) palladacycles (C1–C4) were designed and synthesized with simple anchoring ligands L1–4H (L1H = 2-((2-(4-methoxybenzylidene)-1-phenylhydrazinyl)methyl)pyridine, L2H = N,N-dimethyl-4-((2-phenyl-2-(pyridin-2-ylmethyl)hydrazono)methyl)aniline, L3H = N,N-diethyl-4-((2-phenyl-2-(pyridin-2-ylmethyl)hydrazono)methyl) aniline and L4H = 4-(4-((2-phenyl-2-(pyridin-2-ylmethyl)hydrazono) methyl)phenyl)morpholine H = dissociable proton). Molecular structure of catalysts (C1–C4) were further established by single X-ray crystallographic studies. The catalytic performance of palladacycles (C1–C4) was explored with the direct Csp2–H arylation of imidazoles with aryl halide derivatives. These palladacycles were also applied for investigating of Mizoroki–Heck reactions with aryl halides and acrylate derivatives. During catalytic cycle in situ generated Pd(0) nanoparticles were characterized by XPS, SEM and TEM analysis and possible reaction pathways were proposed. The catalyst was employed as a pre-catalyst for the gram-scale synthesis of octinoxate, which is utilized as a UV-B sunscreen agent.
- Maji, Ankur,Singh, Ovender,Singh, Sain,Mohanty, Aurobinda,Maji, Pradip K.,Ghosh, Kaushik
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p. 1596 - 1611
(2020/04/29)
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- Palladium complexes of chalcogenoethanamine (S/Se) bidentate ligands: Applications in catalytic arylation of C[sbnd]H and O[sbnd]H bonds
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This report describes the syntheses of N,E (E = S, Se) coordinated bidentate palladium complexes, by the reaction of N-(2-bromobenzyl)-2-(phenylthio/selanyl)ethanamine (3, 4) with [PdCl2(CH3CN)2]. The new ligands and palladium complexes were characterized by techniques like 1H, 13C{1H} NMR, IR, and elemental analysis. The coordination modes of ligand with palladium precursor in complexes 5 and 6 were authenticated by single crystal X-ray diffraction. The complexes possess distorted square planar geometry around palladium center. Thermally robust and air stable complexes 5 and 6 were used as catalyst for regioselective arylation of imidazole and O-arylation of phenol. In case of regioselective arylation of imidazole, the reaction proceeds smoothly under mild reaction conditions, only 2.0 mol% of catalyst loading is required to achieve high yield (76–92%). This protocol is applicable to a broad substrate scope showing excellent tolerance towards different functional groups. Whereas for O-arylation of phenol also only 2.0 mol% catalyst loading is sufficient to give good yield (71–92%) with excellent tolerance towards a broad range of functional groups. Among sulfur and selenium coordinated ligands, selenium ligand coordinated complex, was found to outperform the catalytic reactions in both cases as compare to sulfur ligand. The mercury and triphenylphosphine poisoning tests suggest homogeneous nature of catalysis.
- Bhatt, Ramprasad,Bhuvanesh, Nattamai,Himanshi,Joshi, Hemant,Sharma, Alpesh K.
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- Developing Bis(imino)acenaphthene-Supported N-Heterocyclic Carbene Palladium Precatalysts for Direct Arylation of Azoles
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On the basis of the strategy of developing highly efficient protocol for Pd-catalyzed cross-coupling reactions, a series of bulky bis(imino)acenaphthene (BIAN)-supported Pd-PEPPSI complexes were synthesized, characterized, and applied in direct arylation
- Hu, Li-Qun,Deng, Rong-Li,Li, Yan-Fen,Zeng, Cui-Jin,Shen, Dong-Sheng,Liu, Feng-Shou
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p. 214 - 226
(2018/02/06)
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- Palladium(II) Complexes of N-Heterocyclic Carbene Amidates Derived from Chalcogenated Acetamide-Functionalized 1 H-Benzimidazolium Salts: Recyclable Catalyst for Regioselective Arylation of Imidazoles under Aerobic Conditions
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The chalcogenated acetamide-functionalized 1H-benzimidazolium salt precursors [1-(CH2C(O)NH(CH2)2S/SePh)-3-R-C7H5N2]+ X (L1-L4; R = Me, CH2Ph; X = Br, I) to C,N,S/Se l
- Bhaskar, Renu,Sharma, Alpesh K.,Singh, Ajai K.
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p. 2669 - 2681
(2018/09/10)
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- Sterically Encumbered Tetraarylimidazolium Carbene Pd-PEPPSI Complexes: Highly Efficient Direct Arylation of Imidazoles with Aryl Bromides under Aerobic Conditions
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A series of sterically encumbered tetraarylimidazolium carbene Pd-PEPPSI complexes were conveniently prepared and fully characterized. These sterically encumbered Pd-PEPPSI complexes act as active precatalysts for the direct arylation of imidazoles with aryl bromides under aerobic conditions. The catalytic performance of Pd-PEPPSI complexes in cross-coupling processes is investigated. Under the optimal protocols, the cross-coupling reactions regioselectively produced C5-arylation products in moderate to excellent yields, which could tolerate a wide range of functional aryl bromides.
- He, Xu-Xian,Li, Yinwu,Ma, Bei-Bei,Ke, Zhuofeng,Liu, Feng-Shou
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supporting information
p. 2655 - 2663
(2016/09/04)
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- One pot Pd(OAc)2-catalysed 2,5-diarylation of imidazoles derivatives
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The regioselective 2- or 5-arylation of imidazole derivatives with aryl halides using palladium catalysts has been described in recent years; whereas the arylation at both C2 and C5 carbons of imidazoles in high yields has not been performed. We found con
- Takfaoui, Abdelilah,Zhao, Liqin,Touzani, Rachid,Soulé, Jean-Fran?ois,Dixneuf, Pierre H.,Doucet, Henri
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p. 8316 - 8323
(2015/03/04)
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- 5-MEMBERED HETEROARYLS AND THEIR USE AS ANTIVIRAL AGENTS
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Compounds of formula (I): or salts thereof are disclosed. Also disclosed are pharmaceutical compositions comprising a compound of formula I, processes for preparing compounds of formula I, intermediates useful for preparing compounds of formula I and therapeutic methods for treating a Retroviridae viral infection including an infection caused by the HIV virus.
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Paragraph 0236; 0237
(2014/07/23)
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- Regioselective synthesis of 4,5-diaryl-1-methyl-1H-imidazoles including highly cytotoxic derivatives by Pd-catalyzed direct C-5 arylation of 1-methyl-1H-imidazole with aryl bromides
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A general and efficient three-step procedure for the highly regioselective synthesis of 1-methyl-1H-imidazoles possessing electron-rich, electron-neutral, and/or electron-deficient aryl moieties at their 4- and 5-positions is described. The first step involves the Pd-catalyzed direct C-5 arylation of commercially available 1-methyl-1H-imidazole with aryl bromides, and the second and third steps of the sequence involve the selective C-4 bromination of the resulting 5-aryl-1-methyl-1H-imidazoles with NBS, followed by a PdCl 2(dppf)-catalyzed Suzuki-type reaction between 5-aryl-4-bromo-1- methyl-1H-imidazoles and arylboronic acids under phase-transfer conditions. Two 4,5-diaryl-1-methyl-1H-imidazoles so prepared, which can be regarded as Z-restricted analogues of naturally occurring combretastatin A-4 (CA-4), proved to be highly cytotoxic against a variety of human tumor cell lines, and one of these derivatives has been shown to be more cytotoxic than CA-4 and all of the imidazole derivatives investigated in the literature thus far. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Bellina, Fabio,Cauteruccio, Silvia,Di Fiore, Annarita,Rossi, Renzo
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supporting information; experimental part
p. 5436 - 5445
(2009/05/07)
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