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showing 10 items of 533 documents
ChemInform Abstract: Tandem Asymmetric Michael Reaction-Intramolecular Michael Addition. An Easy Entry to Chiral Fluorinated 1,4-Dihydropyridines.
2010
The sequential treatment of optically active sulfoxide (I) with fluorinated nitriles and alkyl propiolates affords (sulfinylmethyl)dihydropyridines of type (IV) as single diastereomers in most cases.
Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid
1997
The reaction mechanism for the decomposition of 2-chloropropionic acid in the gas phase to form hydrogen chloride, carbon monoxide, and acetaldehyde has been theoretically characterized. Analytical gradients have been used by means of AM1 and PM3 semiempirical procedures and ab initio methods at HF and DFT (BLYP) levels with the 6-31G** basis set. The correlation effects were also included by using the perturbational approach at the MP2 level with the 6-31G** and 6-31++G** basis sets and the variational approach at the CISD/6-31G** level and by means of MCSCF wave functions with a (6,6) complete active space and the 6-31G** basis set. The global potential energy surface has been studied, an…
Theoretical Studies of the Electronic Spectra of Organic Molecules
1995
The complete active space (CAS) SCF method in conjunction with multiconfigurational second-order perturbation theory (CASPT2) has been used to study the electronic spectra of a large number of molecules. The wave functions and the transition properties are computed at the CASSCF level, while dynamic correlation contributions to the excitation energies are obtained through the perturbation treatment. The methods yield energies, which are accurate to at least 0.2 eV, except in a few cases, where the CASSCF reference function does not characterize the electronic state with sufficient accuracy. The applications comprise: the polyenes from ethene to octatetraene (cis- and trans-forms); a number …
1,2-Asymmetric Induction in Diastereoselective Zwitterionic Aza-Claisen Rearrangements: Key Steps in Optically Active Alkaloid Synthesis
2013
The zwitterionic aza-Claisen rearrangement of optically active N-allylpyrrolidines and α-phenoxyacetyl fluorides proceeds with complete simple diastereoselectivity (internal asymmetric induction) and complete 1,2-asymmetric induction to generate a new C–C bond adjacent to a chiral C-N-Boc functionality. The resulting γ,δ-unsaturated amides were cyclised to give the corresponding pyrrolizidinones, which enabled the determination of the relative configuration of the stereotriads. Vinyl group degradation and a final lactam reduction gave an optically active analogue of (+)-petasinine (a pyrrolizidine alkaloid). Furthermore, the stereotriad-containing amides should be useful key intermediates f…
ChemInform Abstract: A New Tandem Cross Metathesis-Intramolecular Aza-Michael Reaction for the Synthesis of α,α-Difluorinated Lactams.
2012
Difluorinated amides are treated with methyl vinyl ketone or analogous esters to produce the desired γ- and δ-lactam units including optically active versions.
Kinetische Racematspaltungen ausgehend vonrac-Alkoholen oderrac-Carbonsäurehalogeniden unter Mitwirkung optisch aktiver Induktorbasen
1989
Bei der Umsetzung eines Molaquivalents achiraler Carbonsaurehalogenide mit zwei Molaquivalenten rac-Alkoholen entstehen unter Mitwirkung von einem Molaquivalent einer optisch aktiven Induktorbase (tertiares Amin) partiell optisch aktive Ester sowie partiell optisch aktive Alkohole in zum Teil hoher optischer Reinheit (60 – 70%). Der im Ester gebundene Anteil an Alkohol sowie der nicht umgesetzte Alkohol haben entgegengesetzte Konfiguration. Der Induktionsgrad ist ahnlich hoch, wenn man zwei Molaquivalente eines rac-Carbonsaurehalogenids mit je einem Molaquivalent eines achiralen Alkohols und einer Induktorbase umsetzt. Der Carbonsaureanteil im Ester und die freie Saure haben entgegengesetzt…
An efficient entry to optically active anti- and syn-beta-amino-alpha-trifluoromethyl alcohols.
2008
The reaction of chiral 5,6-dihydro-2H-1,4-oxazin-2-ones with TMSCF3 in the presence of a suitable activator leads to trifluoromethyl lactols, which can be selectively reduced to anti-beta-amino-alpha-trifluoromethyl alcohols. The corresponding syn diastereoisomers are obtained when the starting imines are reduced and the nitrogen atom is conveniently protected. In addition, a novel rearrangement of the CF3 group in the lactol intermediates has been observed. This represents a formal CF3 addition to the imine function in the starting substrates.
Studien zum Vorgang der Wasserstoffübertragung, 41. Elektroreduktion von Acetophenon unter Mitwirkung optisch aktiver Leitsalze
1977
Die Anderung des Carbinol/Pinakol-Verhaltnisses2) (C/P) und der optischen Induktion bei der Elektroreduktion von Acetophenon mit (1 R, 2S)-N-(3-Cyanpropyl)-N-methylephedriniumbromid (1) und (1 R, 2 S)-N,N-Dimethylephedriniumbromid (2) als Leitsalze wird untersucht in Abhangigkeit: a) vom Potential (Tabelle 1), b) von der Stromdichte (Tabelle 2), c) von Pulsbedingungen (Tabelle 3), d) vom pH (Tabelle 4), e) von der Anwesenheit anderer Kationen (Tabelle 5), f) vom Losungsmittel (Tabelle 6), g) von der Temperatur (Tabelle 7) und h) von der Art des Elektrodenmaterials (Tabelle 8). — Es werden tensammetrische und cyclovoltammetrische Messungen durchgefuhrt. Die in trockenem Dimethylformamid erha…
Racemattrennung, Kristallstruktur und histaminartige Wirkung von 4-[1-(2-Aminoethylthio)ethyl]-5-methylimidazol
1983
Es wird die Racemattrennung von 4-[1-(2-Aminoethylthio)ethyl]-5-methylimidazol (1) mittels optisch aktiver Di-O-(p-toluoyl)weinsaure sowie die histaminartige Wirksamkeit der Enantiomeren beschrieben. Von (+)-1 · 2HCl · H2O wurde die Kristallstruktur bestimmt und bis zu einem R-Wert von 0.0483 verfeinert. Danach ist (+)-1R-konfiguriert. Von den beiden Enantiomeren besitzt nur (S)-(−)-1 H1-agonistische Aktivitat. Resolution, Crystal Structure, and Histamine-like Activity of 4-[1-(2-Aminoethylthio)ethyl]-5-methylimidazole The resolution of racemic 4-[1-(2-aminoethylthio)ethyl]-5-methylimidazole (1) using optically active Di-O-(P-toluoyl)tartaric acid as well as the histamine-like activity of t…
Evaluation of remote sensing of vegetation fluorescence by the analysis of diurnal cycles
2008
Chlorophyll fluorescence (ChF) emission is a direct indicator of the photosynthetic activity of vegetation, which is a key parameter of the carbon cycle. This paper analyses chlorophyll fluorescence evolution at leaf level during a complete diurnal cycle in simulated and natural conditions, for two species under different stress conditions. Absolute spectral radiance of the ChF emission is obtained allowing a quantitative derivation of the fluorescence yield of the ChF, which correlates well with established fluorescence instruments. The studied cases show that the ChF emission is mainly driven by the photosynthetic active radiation during the whole cycle, but the fluorescence yield is seve…