- Catalytic Enantio- and Diastereoselective Mannich Addition of TosMIC to Ketimines
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Chiral amines bearing a stereocenter in the α position are ubiquitous compounds with many applications in the pharmaceutical and agrochemical sectors, as well as in catalysis. Catalytic asymmetric Mannich additions represent a valuable method to access such compounds in enantioenriched form. This work reports the first enantio- and diastereoselective addition of commercially available p-toluenesulfonylmethyl isocyanide (TosMIC) to ketimines, affording 2-imidazolines bearing two contiguous stereocenters, one of which is fully-substituted, with high yields and excellent stereocontrol. The reaction, catalyzed by silver oxide and a dihydroquinine-derived N,P-ligand, is broad in scope, operationally simple, and scalable. Derivatization of the products provides enantioenriched vicinal diamines, precursors to NHC ligands and sp3-rich heterocyclic scaffolds. Computations are used to understand catalysis and rationalize stereoselectivity.
- Franchino, Allegra,Chapman, Jack,Funes-Ardoiz, Ignacio,Paton, Robert S.,Dixon, Darren J.
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supporting information
p. 17660 - 17664
(2018/11/10)
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- Synthesis of Quinuclidines by Intramolecular Silver-Catalysed Amine Additions to Alkynes
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A new method has been developed for the synthesis of 2-alkylidenequinuclidines based on a silver triflate catalysed intramolecular hydroamination of 4-(prop-2-ynyl)piperidines. Monosubstituted piperidines reacted less efficiently than cis-disubstituted piperidines, and the reaction was selective for an alkyne moiety, even in the presence of a vinyl group at the 3-position. The hydroamination occurred readily with a terminal alkyne, as well as with an internal alkyne bearing an aliphatic or aromatic group at the terminal carbon atom. Using this silver-catalysed cyclization, a short procedure was developed for the relay synthesis of the cinchona alkaloids dihydroquinidine and dihydroquinine. We report the synthesis of (enantiomerically pure) 2-alkylidenequinuclidines by an intramolecular hydroamination reaction catalysed by silver triflate. After cyclization to the appropriate quinuclidines, the cinchona alkaloids dihydroquinidine and dihydroquinine were obtained in a two-step procedure.
- Breman, Arjen C.,Ruiz-Olalla, Andrea,Van Maarseveen, Jan H.,Ingemann, Steen,Hiemstra, Henk
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p. 7413 - 7425
(2016/02/20)
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- Organocatalytic asymmetric direct vinylogous Michael addition of α,β-unsaturated γ-butyrolactam to nitroolefins
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The first organocatalytic enantioselective direct vinylogous Michael reaction of α,β-unsaturated γ-butyrolactam to nitroolefins is developed using cinchona alkaloids as the catalysts. Both product enantiomers are accessible with moderate to good enantioselectivity.
- Choudhury, Abhijnan Ray,Mukherjee, Santanu
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supporting information; experimental part
p. 7313 - 7320
(2012/10/07)
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- Simple enantiospecific synthesis of sulfides of Cinchona alkaloids
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The native and epi-Cinchona alkaloids were reacted with (ArS) 2/Bu3P in toluene at 65 °C to give the corresponding arylsulfanyl derivatives (15 examples, 31-75%) with complete inversion of configuration at 9-C stereogenic centers. Similar products were also obtained in the enantiospecific nucleophilic substitution of the 9-mesylates of alkaloids with sodium thiolates (4 examples, 73-84%) and no cinchona rearrangement was observed. The chiral thioethers obtained were preliminarily tested as N(sp 3), S-donating chiral ligands in the Pd-catalyzed allylic alkylation of dimethyl malonate with rac-1,3-diphenylprop-2-enyl acetate and gave the product with up to 78% ee. Georg Thieme Verlag Stuttgart.
- Zielinska-Blajet, Mariola,Kucharska, Malgorzata,Skarzewski, Jacek
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p. 1176 - 1182
(2007/10/03)
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- Heterogeneous enantioselective hydrogenation of ethyl pyruvate catalyzed by cinchona-modified Pt catalysts: Effect of modifier structure
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The effect of the structure of chiral modifiers derived from natural cinchona alkaloids on the enantioselectivity and rate of the Pt/Al2O3-catalyzed hydrogenation of ethyl pyruvate was investigated. The influence of the following structural elements was studied: The cinchonidine versus the cinchonine backbone; effect of the nature and the size of substituents attached to C9; effect of partial hydrogenation of the quinoline ring; effects of changes of the substituent at the quinuclidine moiety. The strongest effects on ee and somewhat less on rate were observed for changes in the O-C9-C8-N part of the cinchona alkaloid and for partial or total hydrogenation of the quinoline rings. The nature of the substituents in the quinuclidine part had a comparably minor influence. The solvent was found to have a significant effect on enantioselectivity and rate. In acetic acid, the best results were obtained with O-methyl-10,11-diydrocinchonidine (ee's up to 93%), whereas dihydrocinchonidine was the most effective modifier in toluene. In agreement with a basic model proposed by Pfaltz, it was concluded that the minimal-requirements for an efficient modifier for the hydrogenation of α-keto esters is the presence of a basic nitrogen center close to one or more stereogenic centers and connected to an aromatic system. The results are in qualitative agreement with mechanistic models based on hydrogen-bonding interactions between an adsorbed modifier molecule and adsorbed ethyl pyruvate or its half-hydrogenated intermediate.
- Blaser,Jalett,Lottenbach,Studer
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p. 12675 - 12682
(2007/10/03)
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