Search results for "Elimination"
showing 10 items of 123 documents
Etherification of Functionalized Phenols with Chloroheteroarenes at Low Palladium Loading: Theoretical Assessment of the Role of Triphosphane Ligands…
2011
The present study highlights the potential of robust tridentate ferrocenylphosphanes with controlled conformation as catalytic auxiliaries in CO bond formation reactions. Air-stable palladium triphosphane systems are efficient for selective heteroaryl ether synthesis by using as little as 0.2 mol% of catalyst. These findings represent an economically attractive and clean etherification of functionalized phenols, electron-rich, electron-poor and para-, meta- or ortho-substituted substrates, with heteroaryl chlorides, including pyridines, hydroxylated pyridine, pyrimidines and thiazole. The etherification tolerates very important functions in various positions, such as cyano, methoxy, amino, …
Diastereoselective Synthesis of Dialkylated Bis(phosphino)ferrocenes: Their Use in Promoting Silver-Mediated Nucleophilic Fluorination of Chloroquino…
2017
International audience; The diastereoselective synthesis of dialkylated ferrocenyl bis(phosphane)s bearing aryl, alkyl, and hetero- or polycyclic substituents on the phosphino groups is reported, together with their characterization in the solid state by X-ray structure analysis and in solution by multinuclear NMR spectroscopy. Introduction of various alkyl groups on the ferrocene backbone, namely, tert-butyl, isopropyl, and trimethylsilyl, has a significant influence on the stereoselectivity of the ensuing lithiation/phosphination reactions. Only the introduction of the tert-butyl groups ensures both a high yield and perfect diastereoselectivity, which leads to the exclusive formation of t…
Exploring species-level taxonomy in the Cryptocephalus flavipes species complex (Coleoptera: Chrysomelidae)
2016
In insects, morphological species identification is often challenging. The discrimination of closely related species may be hampered when only subtle differences in phenotypic characters or a continuum in their variability are present. This is exemplified in the Cryptocephalus flavipes species complex (Coleoptera; Chrysomelidae) where, until now, the species have been discriminated only by the yellow pattern on frons, pronotum, and epipleurae. In the present study, the phylogeny of the C. flavipes species complex was resolved through a multi-locus sequence approach, and the inclusion in the group of the phenotypically similar Cryptocephalus quadripustulatus Gyllenhal, 1813 was evaluated. Su…
PHOSPHORORGANISCHE VERBINDUNGEN 1121REAKTIVITÄT UND SELEKTIVITÄT VON VINYLPHOSPHONIUMSALZEN UND VINYLPHOSPHINOXIDEN GEGENÜBER NUCLEOPHILEN
1984
Abstract As a result of competition reactions triphenylvinylphosphonium bromide 1 is SH-selective. But the reactivity is significantly reduced in comparison to the vinyl sulfones. The elimination reaction (b) is also slowed down compared with the cleavage of the corresponding sulfones. In diphenylvinylphosphine oxide 2 the SH-selectivity is preserved. The rate of the reactions (a) and (b) is so extremely slow that 2 has no chance as a SH-protective reagent. Triphenyl-vinylphosphoniumbromid 1 reagiert in Konkurrenzversuchen mit RXH (X=O, S, NH) SH-selektiv bei deutlich reduzierter Reaktivitat im Vergleich zu den Vinylsulfonen. Auch die Eliminierung nach (b) verlauft langsamer als bei analoge…
On the mechanism of imine elimination from Fischer tungsten carbene complexes
2016
(Aminoferrocenyl)(ferrocenyl)carbene(pentacarbonyl)tungsten(0) (CO)5W=C(NHFc)Fc (W(CO)5(E-2)) is synthesized by nucleophilic substitution of the ethoxy group of (CO)5W=C(OEt)Fc (M(CO)5(1Et)) by ferrocenyl amide Fc-NH– (Fc = ferrocenyl). W(CO)5(E-2) thermally and photochemically eliminates bulky E-1,2-diferrocenylimine (E-3) via a formal 1,2-H shift from the N to the carbene C atom. Kinetic and mechanistic studies to the formation of imine E-3 are performed by NMR, IR and UV–vis spectroscopy and liquid injection field desorption ionization (LIFDI) mass spectrometry as well as by trapping experiments for low-coordinate tungsten complexes with triphenylphosphane. W(CO)5(E-2) decays thermally i…
Cyclometalated Au(III) Complexes for Cysteine Arylation in Zinc Finger Protein Domains: Towards Controlled Reductive Elimination
2019
With the aim of exploiting the use of organometallic species for the efficient modification of proteins through C-atom transfer, the gold-mediated cysteine arylation through a reductive elimination process occurring from the reaction of cyclometalated AuIII C^N complexes with a zinc finger peptide (Cys2His2 type) is here reported. Among the four selected AuIII cyclometalated compounds, the [Au(CCON)Cl2] complex featuring the 2-benzoylpyridine (CCON) scaffold was identified as the most prone to reductive elimination and Cys arylation in buffered aqueous solution (pH 7.4) at 37 °C by high-resolution LC electrospray ionization mass spectrometry. DFT and quantum mechanics/molecular mechanics (Q…
Multiple food hypersensitivity as a cause of refractory chronic constipation in adults
2006
Chronic constipation that is unresponsive to laxative treatment is a severe illness, but children unresponsive to laxatives have been successfully treated with an elimination diet. We report the first cases of refractory chronic constipation caused by food hypersensitivity in adults. Four patients with refractory constipation who were unresponsive to high doses of laxatives were put on an oligo-antigenic diet and underwent successive double-blind, placebo-controlled, food challenges (DBPFC). Routine laboratory tests, immunological assays, colonoscopy, esophago-gastroduodenoscopy and rectal and duodenal histology were performed. While on an elimination diet, bowel habits normalized in all pa…
Fecal assays detect hypersensitivity to cow's milk protein and gluten in adults with irritable bowel syndrome.
2011
Background & Aims Some patients with irritable bowel syndrome (IBS)-like symptoms suffer from food hypersensitivity (FH); their symptoms improve when they are placed on elimination diets. No assays identify patients with FH with satisfactory levels of sensitivity. We determined the frequency of FH among patients with symptoms of IBS and the ability of fecal assays for tryptase, eosinophil cationic protein (ECP), or calprotectin to diagnose FH. Methods The study included 160 patients with IBS, 40 patients with other gastrointestinal diseases, and 50 healthy individuals (controls). At the start of the study, patients completed a symptom severity questionnaire, fecal samples were assayed, and …
Reactions of m-Terphenyl-Stabilized Germylene and Stannylene with Water and Methanol: Oxidative Addition versus Arene Elimination and Different React…
2015
Reactions of the divalent germylene Ge(ArMe6)2 (ArMe6 = C6H3-2,6-{C6H2-2,4,6-(CH3)3}2) with water or methanol gave the Ge(IV) insertion product (ArMe6)2Ge(H)OH (1) or (ArMe6)2Ge(H)OMe (2), respectively. In contrast, its stannylene congener Sn(ArMe6)2 reacted with water or methanol to produce the Sn(II) species {ArMe6Sn(μ-OH)}2 (3) or {ArMe6Sn(μ-OMe)}2 (4), respectively, with elimination of ArMe6H. Compounds 1–4 were characterized by IR and NMR spectroscopy as well as by X-ray crystallography. Density functional theory calculations yielded mechanistic insight into the formation of (ArMe6)2Ge(H)OH and {ArMe6Sn(μ-OH)}2. The insertion of an m-terphenyl-stabilized germylene into the O–H bond was…
Food allergy in irritable bowel syndrome: The case of non-celiac wheat sensitivity
2015
Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders, having a prevalence of 12%-30% in the general population. Most patients with IBS attribute their symptoms to adverse food reactions. We review the role of diet in the pathogenesis of IBS and the importance of dietary factors in the management of these patients. The MEDLINE electronic database (1966 to Jan 2015) was searched using the following keywords: "food", "diet", "food allergy", "food hypersensitivity", "food intolerance", "IBS", "epidemiology", "pathogenesis", "pathophysiology", "diagnosis", "treatment". We found 153 eligible papers; 80 were excluded because: not written in English, exclusive biochem…