Search results for "stereo"
showing 10 items of 6147 documents
Enantiospecific Brook Rearrangement of Tertiary Benzylic α-Hydroxysilanes
2018
The Brook rearrangement of simple, chiral tertiary benzylic -hydroxysilanes is presented. The rearrangement followed by proton trapping is enantiospecific and proceeds with inversion of the configuration at the carbon center. Importantly, the [1,2]-Brook rearrangement can be followed by trapping of methyl or allyl electrophiles even in the protic environment, although with minimal retention of chirality.
Reaktionen von elektronenreichen Heterocyclen mit Orthocarbonsäure-Derivaten, 9. Acylierungsreaktionen von Indol und Methylindolen mit Dialkoxycarben…
1986
Indol und einige Methylderivate 1 lassen sich unter milden Bedingungen mit den Dialkoxycarbenium-tetrafluoroboraten 2 in meist guten Ausbeuten regioselektive acylieren. Mit dem Formylkation-Aquivalent 2a′ werden mit uberschussigem 1 auch die Bisindolycarbenium-tetrafluoroborate 13a – d erhalten. Reactions of Electron-rich Heterocycles with Orthocarboxylic Acid Derivatives, 9. – Acylation of Indole and Methylindoles with Dialkoxycarbenium Tetrafluoroborates Indole and some methylindoles 1 were acylated regioselectively with dialkoxycarbenium tetrafluoroborates 2 under mild conditions. The formyl cation equivalent 2a′ reacts with excess of indoles 1 to give the bisindolylcarbenium tetrafluoro…
Derivatisation of Pyrogallarenes
2005
Derivatisation of upper-rim hydroxy groups of pyrogallarenes produced completely acylated and tosylated pyrogallarene derivatives. Mesitylation of pyrogallarene, however, resulted in a regioselective derivatisation of hydroxy groups, i.e. eight OH groups out of 12 were mesitylated. Crystal structures of the synthesised pyrogallarene derivatives indicate that completely substituted pyrogallarenes exist in a distorted crown conformation despite of the lack of stabilising intramolecular hydrogen bonds. In contrast, the partially substituted pyrogallarene adopts a boat conformation and has an open cavity for the inclusion of small guest molecules. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinh…
Antikonvulsiva, 1. Mitt. Thiocarbamoylbutyroguanamine
1986
Durch Anlagerung von Butyroguanamin (1) an die Isothiocyanate 2a-c sind die Thiocarbamoylbutyroguanamine 3a-c zuganglich. Auf dem Wege der Acylierung von 3 sind unsymmetrisch substituierte Butyroguanamine 4 erhaltlich. Unter den neu entwickelten Verbindungen zeichnet sich insbesondere 3c durch antikonvulsive, fungizide und die Magensauresekretion hemmende Wirkungen aus. Anticonvulsivic Agents, I: Thiocarbamoylbutyroguanamines The thiocarbamoylbutyroguanamines 3a-c are accessible by addition of butyroguanamine (1) to the isothiocyanates 2a-c. Unsymmetrically substituted butyroguanamines 4 are obtainable by acylation of 3. Among the newly prepared compounds, 3c in particular exhibits anticonv…
The identification of vicinally substituted cyclohexane isomers in their mixtures by 1H and 13C NMR spectroscopy.
2000
The radical addition reactions of organobromine compounds, XBr (X = CH2COOMe, PhCH2, CHBr2 and CCl3) with cyclohexene afforded mixtures of cis/trans isomer pairs of 1-X-2-Br-cyclohexanes. In addition to benzyl benzoyloxy derivatives are formed also, when benzoyl peroxide is used as an initiator. Owing to the great difficulties in separating these cis/trans isomer pairs, they are identified directly in their mixtures by NMR spectroscopy. In addition to one-dimensional (ID) 1H, proton decoupled 13C and DEPT-135, also two-dimensional (2D) 13C-13C INADEQUATE as well as 1H-13C HMQC experiments have been used in assigning the signals of each compound in their mixtures. The identification of each …
ChemInform Abstract: One-Pot Synthesis of Polysubstituted Indolizines by an Addition/Cycloaromatization Sequence.
2013
Indolizines carrying various substituents in positions 5-8 were obtained from readily available 2-(1H-pyrrol-1-yl)nitriles and α,β-unsaturated ketones or aldehydes in a one-pot procedure. Michael addition of the deprotonated aminonitriles to the acceptors followed by acid-catalyzed electrophilic cyclization produces 5,6-dihydroindolizine-5-carbonitriles. From these stable intermediates, substituted indolizines were obtained via base-induced dehydrocyanation.
ChemInform Abstract: First Reactions of 2,2′-Bisindolyls with Electrophilic Azo Compounds and Diethyl Mesoxalate.
2010
Conformations and some electronic properties of the 2,2′-bisindolyls 6 were calculated for the prediction of probable Diels-Alder reactivity, in analogy to previous work on 2-vinylindoles. First reactions with dienophiles revealed that compounds 6 did not participate in [4 + 2]cycloadditions but rather underwent simple electrophilic substitutions at the enamine function with, above all, some heterodienophiles. Erste Reaktionen von 2,2′-Bisindolylen mit elektrophilen Azoverbindungen und Diethylmesoxalat Zur Vorhersage moglicher Diels-Alder-Reaktionen an 2,2′-Bisindolylen 6 werden Berechnungen zur Konformation und uber elektronische Eigenschaften durchgefuhrt. Die erstmals durchgefuhrten Reak…
ChemInform Abstract: Stereoselective Nucleophilic Addition Reactions of Reactive Pseudopeptides.
2010
Ferrocenylbis(ylene) phosphoranes
1997
The ferrocenylbis(methylene)phosphorane Fc-P(=CTms 2 ) 2 ( 1 ) (Fc = −C 5 H 4 FeC 5 H 5 ) can be synthesized starting from ferrocenyldichlorophosphane FcPCl 2 or ferrocenyldilithiophosphane FcPLl 2 . The X-ray structure of ( 1 ) shows some unusual structural features, which indicate considerable electronic interaction of the ferrocenyl group and the σ 3 λ 5 -phosphorane unit. As a consequence of this interaction, the rotational barrier of the methylene bonds is extraordinary low. Therefore, in contrast to other bis(methylene)phosphoranes, the endo - and exo -Tms groups are indistinguishable on the NMR time scale even at −100°C. The analogous ferrocenylbis(imino)phosphorane Fc-P(=NTms) 2 ( 9…