- Aqueous CO2fixation: construction of pyridine skeletons in cooperation with ammonium cations
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A simple and green method is explored for the synthesis of fused pyridines by [2 + 2 + 1 + 1] the cycloaddition of ketones with an ammonium cation under a CO2atmosphere. The reactions employed ammonium cation as a nitrogen source and CO2gas as a carbon source in an aqueous solution. Monoethanolamine (MEA) was used as an additive to increase the solubility of CO2in an aqueous solution. The scope and versatility of the method are demonstrated with 38 examples. Products are found to be photosensitive and show potential applications as organic optoelectronic materials. A selectfluor-promoted reaction mechanism is proposed based on the experimental studies. Our work is superior as it is a metal-free system, uses CO2as a carbon source and MEA as an additive in aqueous synthesis.
- Fan, Weibin,Guo, Shiwei,Huang, Deguang,Li, Yinghua,Xiang, Shiqun,Zhang, Wei
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supporting information
p. 7950 - 7955
(2021/10/29)
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- Metal-Free Deoxygenation of Chiral Nitroalkanes: An Easy Entry to α-Substituted Enantiomerically Enriched Nitriles
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A metal-free, mild and chemodivergent transformation involving nitroalkanes has been developed. Under optimized reaction conditions, in the presence of trichlorosilane and a tertiary amine, aliphatic nitroalkanes were selectively converted into amines or nitriles. Furthermore, when chiral β-substituted nitro compounds were reacted, the stereochemical integrity of the stereocenter was maintained and α-functionalized nitriles were obtained with no loss of enantiomeric excess. The methodology was successfully applied to the synthesis of chiral β-cyano esters, α-aryl alkylnitriles, and TBS-protected cyanohydrins, including direct precursors of four active pharmaceutical ingredients (ibuprofen, tembamide, aegeline and denopamine).
- Pirola, Margherita,Faverio, Chiara,Orlandi, Manuel,Benaglia, Maurizio
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supporting information
p. 10247 - 10250
(2021/06/18)
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- Organocatalyzed biomimetic selective reduction of c=c double bonds of chalcones
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In this article, we reported a biomimetic approach for chemoselective reduction of C=C double bonds in chalcones under metal and acid free conditions, that relies on olefin activation by hydrogen bond formation. The process requires only catalytic amount of ephedrine as hydrogen bond donor and utilizes Hantzsch esters for transfer hydrogenation.
- Tripathi, Vishwa Deepak,Jha, Anand Mohan
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p. 2322 - 2324
(2018/09/09)
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- A Continuous-Flow, Two-Step, Metal-Free Process for the Synthesis of Differently Substituted Chiral 1,2-Diamino Derivatives
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The enantioselective organocatalytic reduction of aryl-substituted nitroenamines was successfully performed under continuous-flow conditions. After a preliminary screening with a 10-μL microreactor, to establish the best reaction conditions, the reduction was scaled up in a 0.5-mL mesoreactor, without appreciable loss of enantioselectivity, that remained constantly higher than 90%. The in-flow nitro reduction was also accomplished, either by Raney nickel catalyzed hydrogenation or by a metal-free methodology based on the use of the very inexpensive and readily available reducing agent trichlorosilane. The final aim is to develop a two-step, continuous-flow process for the stereoselective, metal-free, catalytic synthesis of differently functionalized chiral 1,2-diamines.
- Pirola, Margherita,Compostella, Maria Elena,Raimondi, Laura,Puglisi, Alessandra,Benaglia, Maurizio
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supporting information
p. 1430 - 1438
(2018/02/09)
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- Frustrated Lewis Pair Catalyzed Dehydrogenative Oxidation of Indolines and Other Heterocycles
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An acceptorless dehydrogenation of heterocycles catalyzed by frustrated Lewis pairs (FLPs) was developed. Oxidation with concomitant liberation of molecular hydrogen proceeded in high to excellent yields for N-protected indolines as well as four other substrate classes. The mechanism of this unprecedented FLP-catalyzed reaction was investigated by mechanistic studies, characterization of reaction intermediates by NMR spectroscopy and X-ray crystal analysis, and by quantum-mechanical calculations. Hydrogen liberation from the ammonium hydridoborate intermediate is the rate-determining step of the oxidation. The addition of a weaker Lewis acid as a hydride shuttle increased the reaction rate by a factor of 2.28 through a second catalytic cycle.
- Maier, Alexander F. G.,Tussing, Sebastian,Schneider, Tobias,Fl?rke, Ulrich,Qu, Zheng -Wang,Grimme, Stefan,Paradies, Jan
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supporting information
p. 12219 - 12223
(2016/10/13)
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- Organocatalytic Enantioselective Transfer Hydrogenation of β-Amino Nitroolefins
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The asymmetric organocatalytic transfer hydrogenation of β-acylamino and β-tert-butyloxycarbonylamino nitroolefins has been successfully realised in excellent enantioselectivities and yields (up to >99% ee, 97% yield) with a simple thiourea catalyst and a Hantzsch ester as hydrogen source, giving a direct access to enantiomerically pure β-amino nitroalkanes. (Figure presented.).
- Ferraro, Antonino,Bernardi, Luca,Fochi, Mariafrancesca
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supporting information
p. 1561 - 1565
(2016/10/13)
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- Selective Debromination and α-Hydroxylation of α-Bromo Ketones Using Hantzsch Esters as Photoreductants
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Two transformations initiated by photoinduced one-electron transfer to α-bromo ketones have been demonstrated. Hantzsch esters donate one electron to α-bromo ketones under photoirradiation, promoting reductive debromination. Subsequent reactions of the resulting radical species of the ketones with molecular oxygen and Hantzsch esters lead to α-hydroxylation or debromination, respectively. The relative dominance of the two pathways depends profoundly on the reaction conditions, including solvent, O2 levels, and the concentration of the Hantzsch esters. The synthetic protocols feature advantages because they require the environmentally benign sources, molecular oxygen and visible light.
- Jung, Jaehun,Kim, Jun,Park, Gyurim,You, Youngmin,Cho, Eun Jin
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supporting information
p. 74 - 80
(2016/01/25)
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- Laccase-catalyzed oxidation of Hantzsch 1,4-dihydropyridines to pyridines and a new one pot synthesis of pyridines
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The laccase-catalyzed oxidation of 1,4-dihydropyridines to pyridines using aerial O2 as the oxidant exclusively delivers pyridines with yields up to 95% under mild reaction conditions. Combination of the Hantzsch 1,4-dihydropyridine synthesis with the newly developed laccase-catalyzed oxidation forms the basis of a facile and environmentally benign method for the synthesis of pyridines in one pot.
- Abdel-Mohsen, Heba T.,Conrad, Juergen,Beifuss, Uwe
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supporting information
p. 2686 - 2690,5
(2020/09/14)
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- Single nucleotide-catalyzed biomimetic reductive amination
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We have successfully developed a single nucleotide (adenosine 5'-diphosphate)-catalyzed enantioselective direct reductive amination of aldehydes and ketones using a Hantzsch ester as reducing agent. The process is a simple, efficient and a real mimic of the NADH reduction approach for the synthesis of structurally diverse amines. This reaction is the first report demonstrating the ability of a single nucleotide as catalyst and one of the most genuine biomimetic reactions of organic chemistry.
- Kumar, Atui,Sharma, Siddharth,Maurya, Ram Awatar
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supporting information; experimental part
p. 2227 - 2232
(2010/11/24)
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- Efficient synthesis of Hantzsch esters and polyhydroquinoline derivatives in aqueous micelles
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Hantzsch 1,4-dihydropyridine and polyhydroquinoline derivatives were synthesized in excellent yields in aqueous micelles. The reaction is catalyzed by PTSA and strongly accelerated by ultrasonic irradiation. Georg Thieme Verlag Stuttgart.
- Kumar, Atul,Maurya, Ram Awatar
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p. 883 - 885
(2008/12/22)
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- Hydrogen transfer from hantzsch 1,4-dihydropyridines to carbon-carbon double bonds under microwave irradiation
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1,4-Dihydropyridines (DHPs) have been used in the reduction of carbon-carbon double bonds under microwave irradiation without solvent. The efficiency of the reactions is dramatically dependent on the steric effects in the DHPs and on the electronic effects in the olefins.
- Torchy, Severine,Cordonnier, Guy,Barbry, Didier,Vanden Eynde, Jean Jacques
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p. 528 - 533
(2007/10/03)
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