Search results for "synthesis"
showing 10 items of 2844 documents
ChemInform Abstract: Enzymatic Biosynthesis of Raumacline
2010
Carbohydrates as Polyfunctional Scaffolds in Combinatorial Synthesis
2006
Carbohydrates are inexpensive, polyfunctional molecules which contain a high density of stereogenic centers. Taking advantage of these particular properties monosaccharides like glucose or mannose have been used for the construction of peptidomimetics which simulate recognition sites of somatostatin or RGD ligands of integrins. Due to their poly functionality, carbohydrates are considered promising scaffolds for combinatorial syntheses either in solution or on solid phase. The application of carbohydrate scaffolds, however, requires sets of orthogonally stable, selectively removable protecting groups, and the challenge in this combinatorial strategy increases with increasing number of hydro…
Ring Expansion of 1,2,3,4-Tetrahydroisoquinolines to Dibenzo[c,f]azonines. An Unexpected [1,4]-Sigmatropic Rearrangement of Nitrile-Stabilized Ammoni…
2014
When the products of a Strecker reaction of 1,2,3,4-tetrahydroisoquinolines with aromatic aldehydes are quaternized with alkyl triflates and subsequently treated with base, a ring expansion to 6,7,8,13-tetrahydro-5H-dibenzo[c,f]azonine-5-carbonitriles takes place. The nine-membered cyclic products can be obtained in good yields (78-89%) in a process involving the [1,4]-sigmatropic rearrangement of a nitrile-stabilized ammonium ylide. The reaction sequence provides a new, simple, and efficient method for the synthesis of these unusual N-heterocycles.
Structure elucidation of benzopyran-2-ol in solution and in solid state following the reduction of coumarin by DIBAL-H
2001
Lactols are compounds of increasing interest in the synthesis of active pharmaceutical derivatives. Nevertheless, the product obtained by the reduction of the carbonyl group of coumarin has been described only twice, and without definition of its precise chemical structure. Since these studies, doubts have been raised about the existence of a monomeric or dimeric form. Our study has led us to conclude definitely that the single dimeric form exists and to precisely define the spectral properties of the two diastereoisomers.
Enantioselective addition of sodium bisulfite to nitroalkenes. A convenient approach to chiral sulfonic acids
2021
An enantioselective organocatalytic addition of sodium bisulfite to (E)-nitroalkenes has been developed by using a chiral bifunctional organocatalyst. The present methodology provides a variety of chiral β-nitroethanesulfonic acid compounds (17 examples) with excellent results: up to 99% yield and excellent enantioselectivity (up to 96% ee). The reaction tolerates (hetero)aryl and alkyl substituents on the β-nitroalkenes, and β,β-disubstituted nitroalkenes.
ChemInform Abstract: A Catalyst Designed for the Enantioselective Construction of Methyl- and Alkyl-Substituted Tertiary Stereocenters.
2016
Tertiary methyl-substituted stereocenters are present in numerous biologically active natural products. Reported herein is a catalytic enantioselective method for accessing these chiral building blocks using the Mukaiyama-Michael reaction between silyl ketene thioacetals and acrolein. To enable remote enantioface control on the nucleophile, a new iminium catalyst, optimized by three-parameter tuning and by identifying substituent effects on enantioselectivity, was designed. The catalytic process allows rapid access to chiral thioesters, amides, aldehydes, and ketones bearing an α-methyl stereocenter with excellent enantioselectivities, and allowed rapid access to the C4-C13 segment of (-)-b…
ChemInform Abstract: Applications and Stereoselective Syntheses of P-Chirogenic Phosphorus Compounds
2016
Phosphorus compounds bearing chirality on the P-center are usually qualified as P-chirogenic or P-stereogenic. This chemical class concerns natural products, agrochemistry, molecular materials, biology and pharmacy, although it is certainly in coordination chemistry and in asymmetric catalysis using chiral transition metal complexes that P-chirogenic phosphorus compounds are the most used. The chiral phosphine ligands and their uses in asymmetric metal-catalyzed reactions have been widely reviewed in literature. However, an overview covering the applications as well as the stereoselective syntheses of all classes of phosphorus compounds has not yet been provided. This review reports the bes…
ChemInform Abstract: Enantioselective Syntheses of 2-Alkyl-, 2,6-Dialkylpiperidines and Indolizidine Alkaloids Through Diastereoselective Mannich-Mic…
2010
Die 2-(Triphenylphosphonio)isopropyloxycarbonyl-(Ppoc-)-Gruppe und am Phosphoniumzentrum modizifierte analoge Reste als Aminoschutzgruppen bei der Pe…
1985
Die Einfuhrung in Aminosauren, die Stabilitat bei Peptidsynthesen und die selektive Abspaltung der 2-(Triphenylphosphonio)isopropyloxycarbonyl-(Ppoc-)-Aminoschutzgruppe sowie ihrer Varianten mit (Methyl)(diphenyl)phosphonium- und (Dimethyl)(phenyl)phosphoniumkopfen werden beschrieben. Der Ppoc-Rest ist in etwa um den Faktor 4 basenstabiler als der entsprechende 2-(Triphenylphosphonio)ethoxycarbonyl-(Peoc-)Rest. Er kann dennoch bereits bei pH = 8 in wasrig-methanolischer Hydrogencarbonatlosung von der blockierten Aminofunktion abgelost werden. Im Gegensatz zur Peoc-Abspaltung treten dabei keine storenden Nebenreaktionen des entstehenden Propenylphosphoniumsalzes mit der freigesetzten Aminofu…
Phase selective synthesis of ZnS nanoparticles from structurally new dithiocarbamate precursor
2015
Abstract A phase selective solvothermal synthesis of ZnS (wurzite) nanoparticles with a flower-like morphology using a dithiocarbamate precursor, [Zn(4-dpmpzdtc)2(dpmpz)] (1) (where, dpmpz=(diphenylmethyl)piperazine), is described. The nanoparticles were identified as ZnS (wurzite) with the particle size of about 3 to 10 nm by scanning and transmission electron microscopy as well as powder X-ray diffraction (XRD). In addition, the precursor complex 1 was characterized using single crystal X-ray diffraction.