Search results for "stereochemistry"
showing 10 items of 4831 documents
Exploiting the CNC Side Chain in Heterocyclic Rearrangements: Synthesis of 4(5)-Acylamino-imidazoles
2010
A new variation on the Boulton-Katritzky reaction is reported, namely, involving use of a CNC side chain. A novel Montmorillonite-K10 catalyzed nonreductive transamination of a 3-benzoyl-1,2,4-oxadiazole afforded a 3-(alpha-aminobenzyl)-1,2,4-oxadiazole, which was condensed with benzaldehydes to afford the corresponding imines. In the presence of strong base, these imines underwent Boulton-Katritzky-type rearrangement to afford novel 4(5)-acylaminoimidazoles.
Pyrrolo[3,4-e][1,2,3]triazolo[1,5-a]pyrimidine and pyrrolo[3,4-d] [1,2,3]triazolo[1,5-a]pyrimidine. New tricyclic ring systems of biological interest
2000
Derivatives of the new ring system pyrrolo[3,4-e][1,2,3] triazolo[1,5-a]pyrimidine 6 were prepared in high yields in one step by reaction of 3-azidopyrrole 3 and substituted acetonitriles. Compound 6b rearranged, upon heating in dimethyl sulfoxide in the presence of water, to pyrrolo[3,4-d][1,2,3]triazolo-[1,5-a]pyrimidine 7.
ChemInform Abstract: Pyrrolo[3,4-e][1,2,3]triazolo[1,5-a]pyrimidine and Pyrrolo[3,4-d][1,2,3]triazolo[1,5-a]pyrimidine. New Tricyclic Ring Systems of…
2001
Derivatives of the new ring system pyrrolo[3,4-e][1,2,3] triazolo[1,5-a]pyrimidine 6 were prepared in high yields in one step by reaction of 3-azidopyrrole 3 and substituted acetonitriles. Compound 6b rearranged, upon heating in dimethyl sulfoxide in the presence of water, to pyrrolo[3,4-d][1,2,3]triazolo-[1,5-a]pyrimidine 7.
Arabinosylamine in Asymmetric Syntheses of Chiral Piperidine Alkaloids.
2004
The stereodifferentiating potential of arabinosyl aldimines was utilized in stereoselective syntheses of 2-substituted dehydropiperidinones and their further transformation to 2,6-cis-substituted piperidinones. The absolute configuration was proven by X-ray analysis and by the synthesis of the enantiomerically pure alkaloid (+)-dihydropinidine. The presented method offers the possibility to synthesize piperidine derivatives enantiomeric to those obtained by the application of the corresponding galactosylamine auxiliary.
ChemInform Abstract: A Stereoselective Synthesis of (+)-Malyngolide via a Ring-Closing Olefin Metathesis.
2000
Abstract A very short and stereoselective synthesis of the non-natural enantiomer of malyngolide from l -erythrulose is described. Key features of the synthesis are the Felkin–Anh diastereoselective allylation of a polyoxygenated ketone and the allylation/metathesis/allylic oxidation protocol recently described by our group.
Novel Porphyrin-Cholic Acid Conjugates as Receptors for Biologically Important Anions
2005
A series of novel receptors showing high binding affinity in aqueous media for biologically important anions are reported. These naturally chromophoric porphyrin-based receptors contain cholic acids connected via quaternary alkyl ammonium amido linkages.
An Uncommon Pathway in the Biosynthesis of Acetylenic Fatty Acids in Mosses
1995
Although more than 600 acetylenic compounds of various structures have been found in plants [1], hardly anything is known about the formation of the triple bonds. The acetylenes so far known from Bryophytes, have been identified as long chain fatty acids with a characteristic arrangement of one triple bond and one to three double bonds.
The Synthesis of Bioactive Sesquiterpenes from Santonin
2000
Abstract This article reviews the literature published in the last decade dealing with the transformation of α-santonin into bioactive or potentially bioactive sesquiterpenes. A number of syntheses starting from 8α-hydroxysantonin (artemisin) have also been included. Special emphasis has been placed on synthesized products that show biological activity. Major advances in this field include the application of new reagents and methodologies for the structural modification of the santonin skeleton and functionality, and its transformation into other sesquiterpenes, especially sesquiterpene lactones. The review has been organised into five parts: 1. Introduction: An overview of the structure an…
Mukaiyama-type, eight-membered ring closure: Access to a tricyclic system related to taxanes
1998
Abstract Addition of Me2CuLi, with in situ trapping by TMSCl, to Hagemann's ester derivative 13, furnished silyl enol ether 14. Mukaiyama-type cyclization of the latter compound gave the tricyclic derivative 15, structurally related to the taxane core.
Über einige niedermolekulare modellverbindungen für polyacroleine. Polymere acroleine. 24. mitt.
1962
Fur die in Redoxpolymerisaten des Acroleins diskutierten Grundbausteine konnen folgende Verbindungen als niedermolekulare Modellsubstanzen betrachtet werden: Isobutyraldehyd, Glutardialdehyd, 2-Hydroxy-tetrahydropyran, 2-(2-Tetrahydropyranyloxy)-tetrahydropyran und 2,6-Dialkoxytetrahydropyrane. An diesen Modellverbindungen werden die mit Polyacroleinen durchgefuhrten Umsetzungen diskutiert. Es ergeben sich Aussagen uber den Reaktionsverlauf, die erzielbaren Umsetzungsgrade und die Zuordnung von IR-Absorptionsbanden. Die Reaktionen der Polyacroleine fuhren danach entweder zu Tetrahydropyran-Derivaten oder zu acyclischen Aldehyd-Derivaten. For the discussed basic units in the redoxpolymer of …