Search results for "Reaction"

Synthesis of new polymers via Diels–Alder reaction. III. Biscyclohexadienephthalimides as dienes

1993

Difunctional cyclohexadienes with dihydrophthalimide central unitsand phenyl side groups to increase solubility are used as bisdienes in repetitive Diels-Alder polyadditions with bis(4-(1,2,4,-triazoline-3,5-dione-4-yl)phenyl)methane as a difunctional dienophile. The polymers show good solubility in CH 2 Cl 2 and CHCl 3 . Non-stoichiometric Diels-Alder polyaddition with slight excess of the bistriazolinedione provides the possibility of synthesizing telechelics with highly reactive triazolinedione end groups

ChemInform Abstract: Carbohydrates as Chiral Templates: Diastereoselective Ugi Synthesis of (S)-Amino Acids Using O-Acylated D-Arabinopyranosylamine …

1990

Abstract Enantiomerically pure (S)-amino acids are synthesized via a highly diastereoselective Ugi reaction using 2,3,4-tri-O-pivaloyl-α-D-arabinopyranosylamine as the chiral template.

Carbohydrates as Stereodifferentiating Auxiliaries

2017

Carbohydrates are inexpensive natural products. Although they contain numerous functional groups and stereogenic centers in one molecule, carbohydrates were recognized as stereodifferentiating auxiliaries much later than other classes of natural products as for example amino acids or terpenes. Apart from their polyfunctional nature carbohydrates are characterized by the anomeric and exo-anomeric effects which have distinct influence of the spatial orientation of substituents linked to the anomeric position. Based on these stereochemical properties carbohydrates were used as stereodifferentiating auxiliaries in numerous diastereoselective reactions, such as aldol addition, alkylation reactio…

ChemInform Abstract: Eco-Friendly Functionalization of Natural Halloysite Clay Nanotube with Ionic Liquids by Microwave Irradiation for Suzuki Coupli…

2014

Abstract Microwave assisted halloysite (HNT) external surface functionalization with ionic liquids is described. HNTs modification was achieved in two steps: a) grafting of 3-mercaptopropyl trimethoxysilane on the external surface of HNT by a microwave irradiation; b) anchorage of vinylimidazolium ionic liquids by a thiol-ene reaction. MW irradiation allowed us to obtain high loading onto the HNT surface compared to those obtained through conventional synthesis. Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed that the grafting has occurred only on the external surface of HNT. Turbidimetric and dynamic light scattering analyses showed that the introduction of…

Eco-friendly functionalization of natural halloysite clay nanotube with ionic liquids by microwave irradiation for Suzuki coupling reaction

2014

Abstract Microwave assisted halloysite (HNT) external surface functionalization with ionic liquids is described. HNTs modification was achieved in two steps: a) grafting of 3-mercaptopropyl trimethoxysilane on the external surface of HNT by a microwave irradiation; b) anchorage of vinylimidazolium ionic liquids by a thiol-ene reaction. MW irradiation allowed us to obtain high loading onto the HNT surface compared to those obtained through conventional synthesis. Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed that the grafting has occurred only on the external surface of HNT. Turbidimetric and dynamic light scattering analyses showed that the introduction of…

Synthesis of new soluble polybenzyls by Friedel-Crafts reactions

1999

Soluble polybenzyls were prepared by a catalytic electrophilic Friedel-Crafts type polycondensation between α,α'-dichloro-p-xylene and substituted (by an alkyl or an alkoxy side-chain) mesitylene. The influence of the length of the side-chain on the solubility of the polymer was examined. The polymers were found to be soluble in common organic solvents. Polymer characterizations were made by 13 C nuclear magnetic resonance spectroscopy (NMR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and elemental analysis.

Cyclodextrin–calixarene co-polymers as a new class of nanosponges

2014

Hyper-reticulated co-polymers jointly formed by cyclodextrin and calixarene units, which can be considered as a new class of nanosponges, were easily obtained by means of a click chemistry approach. In particular, we succeeded in preparing our materials by exploiting the copper-catalyzed 1,3-dipolar cycloaddition (CuAAC) reaction between heptakis-(6-deoxy)-(6-azido)-beta-cyclodextrin and (5,11,17,23-tetra-tert-butyl)-(25,26,27,28-tetra-propargyloxy)-calix-[4]-arene, mixed in different proportions. These materials were fully characterized by means of combined FT-IR, thermogravimetric, C-13 {H-1} CP-MAS NMR and nitrogen adsorption/desorption techniques. In particular, C-13 {H-1} CP-MAS spectr…

1991

The thermal degradation mechanisms of amphiphilic acrylic copolymers containing mesogenic pyrimidine side chains and hydrophilic 2-hydroxyethyl acrylate (HEA) main-chain spacer units were investigated by thermogravimetry (TG) and pyrolysis-field ionization mass spectrometry (Py-FIMS). The degradation behaviour of these polymers depends on the amount of HEA incorporated. Thermogravimetry revealed that the main decomposition occurs in a single step for the pyrimidine homopolymer, whereas with increasing HEA content a two-step process evolves. The major products identified by Py-FIMS are two alcohols and one olefin split from the aromatic side chains. Depolymerization is only a minor degradati…

Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions.

2012

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with subs…

Selective Formal Transesterification of Fluorinated 2-(Trimethylsilyl)ethyl α-Imino Esters Mediated by TBAF

2008

The scope of the transesterification reaction between beta-fluorinated alpha-imino esters and various electrophiles in the presence of TBAF as fluorine source is described. The reaction is highly selective for alkyl iodides, bromides, and mesylates, while alkyl chlorides react at a significantly slower rate and tosylates do not react under the reaction conditions. This methodology represents a simple and useful alternative for the preparation of a wide variety of fluorinated alpha-imino esters.