Search results for "Cinchona"
showing 10 items of 11 documents
CCDC 1522088: Experimental Crystal Structure Determination
2017
Related Article: Mikk Kaasik, Sandra Kaabel, Kadri Kriis, Ivar Järving, Riina Aav, Kari Rissanen, Tönis Kanger|2017|Chem.-Eur.J.|23|7337|doi:10.1002/chem.201700618
Microwave-Assisted Organocatalytic Enantioselective Intramolecular aza-Michael Reaction with α,β-Unsaturated Ketones
2011
An organocatalytic enantioselective intramolecular aza-Michael reaction of carbamates bearing conjugated ketones as Michael acceptors is described. By using 9-amino-9-deoxy-epi-hydroquinine as the catalyst and pentafluoropropionic acid as a co-catalyst, a series of piperidines, pyrrolidines, and the corresponding benzo-fused derivatives (indolines, isoindolines, tetrahydroquinolines, and tetrahydroisoquinolines) can be obtained in excellent yields and enantioselectivities. In addition, the use of microwave irradiation at 60 °C improves the efficiency of the process giving rise to the final products with comparable yields and enantiomeric excesses. Some mechanistic insights are also consider…
High-performance liquid chromatographic enantiomer separation and determination of absolute configurations of phosphinic acid analogues of dipeptides…
2003
The enantiomers of N-benzyloxycarbonyl-phosphinic pseudodipeptides and their N-benzyloxycarbonyl-α-aminophosphinic acid precursors as well as various other structural analogues were separated on a set of cinchona alkaloid-derived chiral anion-exchangers by HPLC in the reversed-phase mode. Semi-preparative scale chromatography provided single enantiomers in 100 mg quantities. The configurations of the enantiomers were assigned indirectly by enantioselective chromatography on the basis of the elution order and was confirmed by enantiomeric reference compounds.
Organocatalytic Enantioselective Friedel–Crafts Aminoalkylation of Indoles in the Carbocyclic Ring
2016
The first general catalytic method for the, so far elusive, enantioselective Friedel−Crafts functionalization of indoles in the carbocyclic ring is presented. This transformation contrasts with the usual tendency of these heterocycles to react at the azole ring. For this purpose, the four regioisomeric hydroxy carbocyclic-substituted indoles were reacted with several isatinderived ketimines, using a Cinchona alkaloid-based squaramide, in a low 0.5−5 mol % catalyst loading, as a bifunctional catalyst. This methodology allows the functionalization of indoles in every position of the carbocyclic ring in a regio- and enantioselective fashion, by switching only the position of the hydroxy group …
Organocatalytic Enantioselective Synthesis of α-Hydroxyketones through a Friedel−Crafts Reaction of Naphthols and Activated Phenols with Aryl- and Al…
2016
[EN] An efficient organocatalytic asymmetric synthesis of alpha-hydroxyketones has been developed. Quinine-derived thiourea catalyzed the enantioselective Friedel Crafts alkylation of naphthols and activated phenols with aryl- and alkylglyoxal hydrates, providing the corresponding chiral alpha-hydroxyketones with high yields (up to 97%) and excellent enantioselectivities (up to 99% ee).
A combined NMR, DFT, and X-ray investigation of some cinchona alkaloid O-ethers.
2008
Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of sign…
CCDC 1522081: Experimental Crystal Structure Determination
2017
Related Article: Mikk Kaasik, Sandra Kaabel, Kadri Kriis, Ivar Järving, Riina Aav, Kari Rissanen, Tönis Kanger|2017|Chem.-Eur.J.|23|7337|doi:10.1002/chem.201700618
CCDC 880528: Experimental Crystal Structure Determination
2013
Related Article: N.Probst, A.Madarasz, A.Valkonen, I.Papai, K.Rissanen, A.Neuvonen, P.M.Pihko|2012|Angew.Chem.,Int.Ed.|51|8495|doi:10.1002/anie.201203852
CCDC 1522082: Experimental Crystal Structure Determination
2017
Related Article: Mikk Kaasik, Sandra Kaabel, Kadri Kriis, Ivar Järving, Riina Aav, Kari Rissanen, Tönis Kanger|2017|Chem.-Eur.J.|23|7337|doi:10.1002/chem.201700618
CCDC 685194: Experimental Crystal Structure Determination
2009
Related Article: O.Bassas, J.Huuskonen, K.Rissanen, A.M.P.Koskinen|2009|Eur.J.Org.Chem.|2009|1340|doi:10.1002/ejoc.200801220