- Process intensification for the continuous flow hydrogenation of ethyl nicotinate
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Here we report a process intensification study for the selective, partial, and full hydrogenation of ethyl nicotinate using a trickle bed reactor for meso-flow transformations (HEL FlowCAT). The process achieved a throughput of 1219 g d-1 (78 g h-1 of product per g of active catalyst) for the partial hydrogenation to ethyl 1,4,5,6-tetrahydropyridine-3-carboxylate, whereas the productivity for the full hydrogenation process reached a 1959 g d-1 of throughput (408 g h-1 of product per g of active catalyst) on this laboratory-scale flow chemistry platform.
- Ouchi, Takashi,Battilocchio, Claudio,Hawkins, Joel M.,Ley, Steven V.
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- HMPA-catalyzed transfer hydrogenation of 3-carbonyl pyridines and other N-heteroarenes with trichlorosilane
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A method for the HMPA (hexamethylphosphoric triamide)-catalyzed metal-freetransfer hydrogenation of pyridines has been developed. The functional group tolerance of the existing reaction conditions provides easy access to various piperidines with ester or ketone groups at the C-3 site. The suitability of this method for the reduction of other N-heteroarenes has also been demonstrated. Thirty-three examples of different substrates have been reduced to designed products with 45–96% yields.
- Fu, Yun,Sun, Jian
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- Diboron-assisted palladium-catalyzed transfer hydrogenation of N-heteroaromatics with water as hydrogen donor and solvent
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A Pd-catalyzed transfer hydrogenation of various N-heteroaromatic compounds with B2pin2 as a mediator and environmentally benign water as both solvent and hydrogen donor has been disclosed. This reaction proceeded under ambient temperature with a broad range of N-heteroaromatic compounds among which imidazo[1,2-a]pyridine derivatives were for the first time selectively reduced to 5,6,7,8-tetrahydroimidazo[1,2-a]pyridines, which are the core structural motifs of an inhibitor of human O-GlcNAcase. Mechanistic studies suggested that the new protons in products are from water and Pd-H might be the key intermediate with B2pin2 as the H2O activator.
- Xuan, Qingqing,Song, Qiuling
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supporting information
p. 4250 - 4253
(2016/09/09)
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- Continuous flow hydrogenation of functionalized pyridines
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The heterogeneous hydrogenation of substituted pyridines has been accomplished by employing a continuous flow hydrogenation device that incorporates in situ hydrogen generation by electrolysis of H20 and pre-packed catalyst cartridges. In general, the hydrogenation reactions proceeded smoothly regardless of the supported precious metal catalyst (Pd/C, Pt/C, or Rh/C). By using 30-80 bar of hydrogen pressure at 60-80 °C full conversion was typically achieved in all cases at a flow rate of 0.5 mL min -1, providing the corresponding piperidines in high yields. For disubstituted pyr idines, variations in stereoselectivity were observed depending on both the metal catalyst and the temperature/ pressure of the hydrogenation reaction. For ethyl nicotinate the selectivity between partial and full hydrogenation could be tuned depending on the hydrogen pressure, solvent, and the choice of supported metal catalyst. Changing the hydrogen source from H20 to D2C) allowed the preparation of de-uteriated derivatives. Wiley-VCH Verlag GmbH & Co. KGaA.
- Irfan, Muhammed,Petricci, Elena,Glasnov, Toma N.,Taddei, Maurizio,Kappe, C. Oliver
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experimental part
p. 1327 - 1334
(2009/07/19)
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- Asymmetric hydrogenation of pyridines: Enantioselective synthesis of nipecotic acid derivatives
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An asymmetric hydrogenation process of 3-substituted pyridine derivatives has been developed with the use of a Rh-TangPhos complex as the catalyst. The whole process consists of an efficient partial hydrogenation of nicotinate and a subsequent highly enan
- Lei, Aiwen,Chen, Mao,He, Minsheng,Zhang, Xumu
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p. 4343 - 4347
(2007/10/03)
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- Enantioselective homogeneous hydrogenation of monosubstituted pyridines and furans
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The first case of an enantioselective hydrogenation of monosubstituted pyridines and furans with homogeneous rhodium diphosphine catalysts with low but significant enantioselectivities and catalyst activities is reported. Best enantioselectivities (ees of 24-27%) were obtained for the hydrogenation of 2-and 3-pyridine carboxylic acid ethyl ester and 2-furan carboxylic acid with catalysts prepared in situ from [Rh(nbd)2]BF4 and the chiral ligands diop, binap, or ferrocenyl diphosphines of the josiphos type. Turnover numbers (ton) were in the order of 10-20, turnover frequencies (tof) usually 1-2 h-1. Diphosphines giving 6-or 7-ring chelates led to higher ees than 1,2-diphosphines; otherwise, no clear correlation between ligand properties and catalytic performance was found. In some experiments black precipitates were observed at the end of the reaction, indicating the decomposition of the homogeneous catalysts for certain ligand/metal/ substrate combinations.
- Studer, Martin,Wedemeyer-Exl, Christina,Spindler, Felix,Blaser, Hans-Ulrich
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p. 1335 - 1343
(2007/10/03)
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