Search results for "ALK"
showing 10 items of 4314 documents
Asymmetric synthesis of polycyclic 3-fluoroalkylproline derivatives by intramolecular azomethine ylide cycloaddition
2019
The asymmetric synthesis of polycyclic fluorinated proline derivatives has been accomplished by means of an intramolecular azomethine ylide cycloaddition with fluorinated dipolarophiles. Thus, the reaction of benzaldehydes bearing a trifluoromethyl alkene in ortho position with an azomethine ylide precursor derived from chiral 2-amino indanol takes place with excellent levels of diastereoselectivity, with simultaneous generation of four stereocenters. In order to determine the influence of the fluorine moiety in the process, starting material bearing non-fluorinated alkenes were synthesised. In this case, a dramatic drop of selectivity occurred, which indicates that the role of the fluorine…
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.
Bis[(trimethylsilyl)methyl]manganese: Structural Variations of Its Solvent-Free and TMEDA-, Pyridine-, and Dioxane-Complexed Forms
2009
First synthesized in 1976 and recently taking on a new significance as a key precursor to heterobimetallic alkali-metal-manganese(II) complexes, bis[(trimethylsilyl)methyl] manganese has been structurally characterized by X-ray crystallography. It forms a polymeric chain structure of formula [{Mn(CH2SiMe3)(2)}(infinity)], 1, in which distorted tetrahedral, spiro Mn atoms are linked together via mu(2)-bonding alkyl ligands. The structure is notable for displaying two distinct categories of Mn-C bond lengths with a mean size differential of 0.225 angstrom and for being the first fully crystallographically characterized polymeric manganese(II) dialkyl compound. Magnetic measurements of 1 indic…
An efficient synthesis of uracil derivatives from 2-alkyl-Δ2-oxazolines and nitriles
2008
An efficient and convenient synthesis of new fluorinated and non-fluorinated uracils is described herein. The condensation of nitriles with enolates generated from 2-alkyl-Δ 2 -oxazolines (I) affords fluorinated β-enamino acid derivatives, which react with triphosgene to give an isomeric mixture of oxazolopyrimidinones. These can then be easily transformed into a single C-6 pyrimidindione derivative through reaction with a suitable nucleophile.
Reactions of Tris(ethanediolato)tungsten and Tungsten Oxytetrachloride with Aminotris(phenol)s: Alkoxide, Chloro, and Alkyl Derivatives of Oxotungst…
2005
Trisdiolatotungsten(VI) complex [W(eg)3] (eg = 1,2-ethanediolato dianion) reacts in refluxing toluene solution with phenolic ligand precursors tris(2-hydroxy-3,5-dimethylbenzyl)amine (H3LMe) and tris(2-hydroxy-3,5-di-tert-butylbenzyl)amine (H3LtBu) to form monomeric oxotungsten(VI) complexes [WO(LMe)(Heg)] and [WO(LtBu)(Heg)], respectively. These complexes undergo chloride-for-alkoxide substitution when treated with SOCl2 in CH2Cl2, which leads to the formation of corresponding chloro complexes [WO(LMe)Cl] and [WO(LtBu)Cl]. Identical chloro complexes are also formed in the reaction between these phenolic ligand precursors and [WOCl4]. The reaction of [WO(LR)Cl] complexes with Grignard reage…
Mono(cyclopentadienyl) Complexes of the Rare-Earth Metals
2002
I. Introduction 1953II. Overview of Synthesis, Structure, and Properties 1954A. Synthetic Methods 1954B. Ligands and Structures 1955III. Halo Complexes 1956A. General 1956B. Divalent Halo Complexes 1956C. Trivalent Halo Complexes 1957IV. Chalcogenido Complexes 1958A. General 1958B. Divalent Chalcogenido Complexes 1958C. Trivalent Chalcogenido Complexes 1959V. Pnicogenido Complexes 1960A. General 1960B. Divalent Amido and Phosphido Complexes 1960C. Trivalent Pnicogenido Complexes 19611. Bis(amido) Complexes 19612. Mixed Halo and Chalcogenido Complexes 1962VI. Hydrocarbyl and Silyl Complexes 1963A. General 1963B. Divalent Complexes 19631. Metallacarbaboranes 19632. Bimetallic Naphthalene Comp…
Zirconium and hafnium mono(alkyl) complexes containing a tridentate linked amido-tetramethylcyclopentadienyl ligand. Molecular structure of Hf(η5:η1:…
1998
Abstract Zirconium and hafnium complexes M( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)Cl 2 (M=Zr, Hf) containing the tridentate 2-methoxyethylamido-functionalized tetramethylcyclopentadienyl ligand C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe have been synthesized by the reaction of the dilithium derivative Li 2 [C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe] with MCl 4 (THF) 2 . Selective monoalkylation of the dichloro complexes gave complexes of the type M( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)(R)Cl (R=CH 2 Ph, o -C 6 H 4 CH 2 NMe 2 ). The crystal structure of the hafnium dichloro complex Hf( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)Cl 2 has been determined by X-ray crystal diffraction and sho…
Enantioselective Synthesis of Substituted Indoles Through Zirconium(IV)-Catalyzed Friedel–Crafts Alkylation
2012
The chiral complex of ( R )-3,3′-Br 2 -BINOL and zirconium tert -butoxide catalyzes the Friedel–Crafts alkylation of indoles with enones bearing an alkyl or fluorinated group at the β-position to give indoles having a side chain at the C3 position with a tertiary stereogenic center in good yields and with excellent enantioselectivities.
Pyrrolide-imine benzyl complexes of zirconium and hafnium: synthesis, structures, and efficient ethylene polymerization catalysis
2004
Abstract A series of pyrrolyl-imines HL1–6 was prepared by the condensation of pyrrole-2-carboxyaldehyde with different amines. The reaction of 2 equiv of pyrrolyl-imine with tetrabenzyl complexes of hafnium and zirconium M(CH2Ph)4 (M=Hf or Zr) gave dibenzyl complexes (L3–6)2M(CH2Ph)2, which were characterized by NMR spectroscopy and crystal structure analysis. NMR spectra of the complexes with secondary alkyl substituents at the imine nitrogen (isopropyl: 3a, 4-tert-butylcyclohexyl: 4a and 4b) suggest that rapid racemization between Δ and Λ configurations occurs in solution on the NMR time scale. The complexes with pyrrolide-imine ligands with a tertiary alkyl group such as tert-butyl (5a …
Guest-Induced Folding and Self-Assembly of Conformationally Adaptive Macrocycles into Nanosheets and Nanotubes
2017
A conformationally adaptive macrocycle is presented, namely zorb[4]arene, which exists in multiple conformations in the uncomplexed state. The binding cavity of zorb[4]arene is concealed, either due to a collapsed conformation or by self-inclusion. The zorb[4]arene with long alkyl chains manifests itself with surprisingly low melting point and thus exist as an oil at room temperature. Binding of a guest molecule induces the folding and conformational rigidity of zorb[4]arene and leads to well-defined three-dimensional structures, which can further self-assemble into nanosheets or nanotubes upon solvent evaporation, depending on guest molecules and the conformations they can induce.