Search results for "Moiety"
showing 10 items of 621 documents
Pauson–Khand reaction of fluorinated compounds
2020
The Pauson–Khand reaction (PKR) is one of the key methods for the construction of cyclopentenone derivatives, which can in turn undergo diverse chemical transformations to yield more complex biologically active molecules. Despite the increasing availability of fluorinated building blocks and methodologies to incorporate fluorine in compounds with biological interest, there have been few significant advances focused on the fluoro-Pauson–Khand reaction, both in the inter- and intramolecular versions. Furthermore, the use of vinyl fluorides as olefinic counterparts had been completely overlooked. In this review, we collect the advances both on the stoichiometric and catalytic intermolecular an…
Diorganotin(IV) dipeptide complexes with potential antitumour activity
1993
A series of complexes of the dimethylltin(IV) moiety with dipeptides has been synthesized. The dipeptides are L-alanyl-L-histidine (H2AlaHis), L-methionyl-L-methionine (H2MetMet), L-glycyl-L-histidine (H2GlyHis) and L-histidyl-L-glycine (H2HisGly). The complexes have been characterized by IR and 119Sn Mossbauer spectroscopy in the solid state and by 1H NMR in CD3OD and D2O solutions. They consist of monomeric entities, with the tin atom arranged in a pentacoordinated trigonal bipyramidal structure. The dipeptides are coordinated via the amino group, deprotonated peptide nitrogen and carboxylate group. Neither imidazole in histidine-containing dipetides, nor the thioether group in MetMet, is…
Asymmetric diastereodivergent Michael addition of 2-chloromalonate esters to conjugated imines enabled by catalyst metal change
2019
Despite recent progress in asymmetric diastereodivergent reactions leading to products bearing two stereogenic centers, little research has been devoted to processes were a stereogenic center and a double bond are formed. Here, we report the asymmetric diastereodivergent Michael addition of 2-chloromalonate esters to N-tosyl β,γ-unsaturated α-ketimino esters to give chiral α,β-dehydro-α-aminoesters bearing either a Z or E enamine moiety, using pyBOX-metal complexes. Diastereodivergency is achieved by simply changing the metal ion from a trivalent La(III) to a divalent Ca(II) ion, providing the Z or E enamines. Computational studies reveal the crucial role of London interactions between the …
Redox-induced coordination isomerization of a phosphoniobenzophospholide.
2003
1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a…
ChemInform Abstract: Stereoselective Synthesis of 7,11-Guaien-8,12-olides from Santonin. Synthesis of Podoandin and (+)-Zedolactone A.
2001
Photochemical rearrangement of hydroxy ester 2, easily obtained from santonin (1), afforded butenolide 4, a good starting material for the synthesis of 7,11-guaien-8,12-olides. Compound 4 has been transformed into compound 10, which has been used for the synthesis of podoandin (5) and (+)-zedolactone A (ent-6). Regioselective elimination of the acetyl group on C10 afforded directly podoandin (5). For the synthesis of ent-6, a hydroxyl group has been regio- and stereoselectively introduced at the 4α-position through the 3α,4α-epoxide 15. The basic hydrolysis of the 10-acetyl group in compound 18 took place with concomitant intramolecular conjugated addition of the alkoxide to the butenolide …
Cyclodextrin-[60]fullerene conjugates: synthesis, characterization, and electrochemical behavior
2006
Three different functionalized β-cyclodextrins (β-CDs) bearing the C60 moiety linked covalently have been prepared in good yields by reaction between the parent β-CD and [60]fullerene via 1,3-dipolar cycloaddition. These compounds have been fully spectroscopically characterized and their electrochemical behavior has been investigated. Surprisingly, the electrochemical properties of the C60 cage remain unaltered even after chemical functionalization, making these systems very appealing as supramolecular hosts for electron-transfer processes.
Halonium ions as halogen bond donors in the solid state [xl2]y complexes
2015
The utilization of halogen bonding interactions is one of the most rapidly developing areas of supramolecular chemistry. While the other weak non-covalent interactions and their influence on the structure and chemistry of various molecules, complexes, and materials have been investigated extensively, the understanding, utilizations, and true nature of halogen bonding are still relatively unexplored. Thus its final impact in chemistry in general and in materials science has not yet been fully established. Because of the polarized nature of a Z–X bond (Z=electron-withdrawing atom or moiety and X=halogen atom), such a moiety can act as halogen bond donor when the halogen is polarized enough by…
Alternative Motifs for Halogen Bonding
2013
The halogen-bonding interaction is one of the rising stars in supramolecular chemistry. Although other weak interactions and their influence on the structure and chemistry of various molecules, complexes and materials have been investigated thoroughly, the field of halogen bonding is still quite unexplored and its impact on chemistry in general is yet to be fully revealed. In principle, every Y–X bond (Y = electron-withdrawing atom or moiety, X = halogen atom) can act as a halogen-bond donor when the halogen is polarized enough by Y. Perfluorohalocarbons are iconic halogen-bond donor molecules in which Y is a perfluorinated aryl or alkyl moiety and X is either iodine or bromine. In this art…
“Tail–Tail Dimerization” of Ferrocene Amino Acid Derivatives
2010
Acid anhydrides of N-protected 1'-aminoferrocene-1-carboxylic acid (Fca) have been prepared and spectroscopically characterized (protection group Boc, Fmoc, Ac; 4a―4c). The structure of the Boc-derivative 4a has been determined by single-crystal X-ray crystallography. An intramolecular N― H···O hydrogen bond involving the carbamate units results in a ring structure containing the two ferrocene units, the anhydride moiety, and the hydrogen bond. In the crystal, the individual molecules are connected by intermolecular N-H···O hydrogen bonds of the carbamate unit. Experimental and theoretical studies suggest that the ring motif is also a dominant species in solution. Electronic communication a…
Non-Isomorphic Chlorine—Bromine Substitution in the Copper(I) Halideπ-Complexes with 1-Allyl-4-aminopyridinium
2003
By alternating-current electrochemical synthesis crystals of {Cu[H2NC5H4N(C3H5)]Br2}˙H2O (I), {Cu[H2NC5H4N(C3H5)]Br0.65Cl1.35}˙H2O (II) and {Cu[H2NC5H4N(C3H5)]Cl2} (III) π-complexes have been obtained and structurally investigated. The I and II compounds are isostructural and crystallize in a monoclinic sp. gr. P21/c, I: a = 7.359(2)A, b = 12.3880(6)A, c = 13.637(3)A, β = 107.03(1)°, V = 1188.7(4)A3, Z = 4 for C8H13N2OBr2Cu composition, R = 0.0293 for 2140 reflections. II: a = 7.2771(6)A, b = 12.3338(3)A, c = 13.4366(7)A, β = 107.632(2)°, V = 1149.3(1)A3, Z = 4 for C8H13N2Br0.65Cl1.35Cu composition, R = 0.0463 for 2185 reflections. Metal and halogen atoms form centrosymmetric Cu2X4 dimers. …