- Green halogenation of aromatic heterocycles using ammonium halide and hydrogen peroxide in acetic acid solvent
-
The green generation of X+ (X = Br, I) using hydrogen peroxide in aqueous acetic acid allows access to aromatic heterocyclic halides in yields and purities comparable to syntheses employing N-bromosuccinimide. In activated and unsubstituted thiophene rings, regioselectivity is quantitative for positions α to the sulfur; pyrroles also give quantitative reactions, at least initially. Deactivated rings, including furans and thiazoles, as well as thiophenes with strongly electron-withdrawing groups showed little to no reactivity under the conditions investigated. The reaction shows remarkable functional group tolerance (to alcohol, nitro, alkyl, halo, and carbonyl groups), as shown through reaction with substituted phenols. In all bromination reactions, reaction yields and regiochemistry were very similar to reactions involving N-bromosuccinimide in tetrahydrofuran solvent.
- D'Aleo, Danielle N.,Allard, Sheena R.,Foglia, Cassandra C.,Parent, Shawna L.M.,Rohr, David J.,Gottardo, Christine,MacKinnon, Craig D.
-
p. 679 - 683
(2013/08/23)
-
- A convergent approach to (R)-Tiagabine by a regio- and stereocontrolled hydroiodination of alkynes
-
The occurrence of unsaturated systems in natural products combined with the mildness and the wide range of applicability of CeCl3 promoted methodologies suggest several potential future synthetic applications within the field of total synthesis of biologically active molecules. On this concept, the use of CeCl3·7H2O-NaI system as an efficient heterogeneous promoter has been highlighted in the iodofunctionalization of carbon-carbon triple bonds. The study has shown that this method would be particularly interesting for the stereoselective formation of trisubstituted (Z)- or (E)-iodoalkenes by simply changing the nature of the solvent. The methodology has been successfully applied to the synthesis of (R)-1-[4,4-bis-(3-methyl-2-thienyl)-3-butenyl]-3-piperidinecarboxylic acid 1, named (R)-Tiagabine, which is a potent and selective γ-aminobutyric acid (GABA) uptake inhibitor with proven anticonvulsant efficacy in humans. The Royal Society of Chemistry 2010.
- Bartoli, Giuseppe,Cipolletti, Roberto,Di Antonio, Giustino,Giovannini, Riccardo,Lanari, Silvia,Marcolini, Mauro,Marcantoni, Enrico
-
experimental part
p. 3509 - 3517
(2010/08/21)
-
- New synthetic method for the polymerization of alkylthiophenes
-
The polymerization of 2-iodo-3-alkylthiophenes using a Heck-type reaction with Pd(OAc)2/NBu4Br as catalytic system is reported leading to expected functionalized oligomers with good yields.
- Sevignon, Marc,Papillon, Julien,Schulz, Emmanuelle,Lemaire, Marc
-
p. 5873 - 5876
(2007/10/03)
-
- Thallium(III) Trifluoroacetate-Trifluoroacetic Acid in the Chemistry of Polythiophenes. 2. Treatment of 3-Alkylthiophenes and Electron Paramagnetic Resonance Results
-
The treatment of thiophene and 3-alkylthiophenes with thallium(III) trifluoroacetate (TTFA) in trifluoroacetic acid (TFA) gives insoluble and dark powdery solids with oxygen content and electrical conductivities ranging from 10-4 to 10-6 Ω-1 cm-1. Polar and short fractions are negligible. All of them show semiconductivity (10-3Ω-1 cm-1) when doped in iodine atmosphere. Electron paramagnetic resonance (EPR) spectra of either as-synthesized or I2-treated solids display characteristic single and broad lines (ΔHPP, 1.84-7.4 G) with Lorentzian shapes and g-values in the range 2.0028-2.0038. Infrared spectra show characteristic C-H out-of-plane deformations (780 cm-1 for polythiophene and 820-825 cm-1 for poly(3-alkylthiophenes)) in addition to a strong peak at 1650-1690 cm-1 which has not been conclusively assigned. EPR spectra of some disubstituted and tetrasubstituted 2,2′-bithiophene radical cations have been observed and their g-values and coupling constants assigned when the corresponding parent compounds are photolyzed with ultraviolet light in TFA. Photolysis of 3-alkylthiophenes in TFA in the EPR instrument gave the radical cations of 4,4′-dialkyl-2,2′-bithiophenes. In no case, were EPR signals of the isomeric 3,3′-dialkyl- or 3,4′-dialkyl-2,2′-bithiophene radical cations observed, indicating that dimerization of 3-alkylthiophenes occurs through the less sterically hindered 5-position. The presence of two doublet species corresponding to both conformers, syn and anti, in the radical cations is associated with a large barrier to rotation about the C(2)-C(2′) bond.
- Tormo, Jordi,Jesus Moreno,Ruiz, Jordi,Fajari, Lluis,Julia, Luis
-
p. 878 - 884
(2007/10/03)
-
- Convergent synthetic routes to orthogonally fused conjugated oligomers directed toward molecular scale electronic device applications
-
This paper describes the synthetic organic phase of a project directed toward the construction of molecular scale electronic devices. Outlined is a convergent synthetic route to orthogonally fused conjugated organic oligomers. The final systems are to have a potentially conducting chain fused perpendicularly to a second potentially conducting chain via a a bonded network. One of the core segments synthesized is based on a spirobithiophene moiety with a central silicon atom. It is formed by a zirconium-promoted bis(bicyclization) of a tetrapropargylsilane. The second core is a 9,9′-spirobifluorene system. Terminal halide groups provide the linkage points for further extension of the chains via Pd-catalyzed or Pd/Cu-catalyzed cross coupling methods. All four branching arms are affixed to the core in a single operation, thus making the syntheses highly convergent. In the cases of the larger functionalized systems, alkyl substituents on the thiophenes afford soluble materials. In order to prepare the molecules with > 50 A lengths, an iterative divergent/convergent approach had to be utilized for the construction of oligo(thiophene-ethynylene) branching arms. Organopalladium-catalyzed procedures are used extensively for the syntheses of the orthogonally fused compounds.
- Wu, Ruilian,Schumm, Jeffry S.,Pearson, Darren L.,Tour, James M.
-
p. 6906 - 6921
(2007/10/03)
-
- STUDIES OF SOME HINDERED 2,2'-BITHIENYLS AND 3,3'-BRIDGED 2,2'-BITHIENYLS WITH SPECIAL REFERENCE TO THEIR UV SPECTRA AND OXUDATION POTENTIALS
-
Some hindered bithienyl derivatives have been synthesized by cross-coupling reaction of Grignard reagents using NiCl2(Dppp) (dppp= Ph2CH2CH2PPh2) or by reductive dimerization in the presence of Zn/NiCl2(PPh3)2.Their UV spectra and oxidation potentials are discussed in terms of their coplaranity and of the inductive effect of the substituent.Keywords: 2,2'-bithienyls; 3,3'-bridged bithienyls; UV Spectra; Oxidation Potenyials; Sonochemical Grignard Reactions
- Amer, A.,Burkhardt, A.,Nkansah, A.,Shabana, R.,Galal, A.,,et al.
-
-
- Conducting Polymers from Dimethyl-2,2'-bithiophenes
-
Electrochemical oxidation of symmetrical dimethylbithiophenes with free α-positions yields electroactive polymers with excellent cycling ability.
- Krische, Bernd,Hellberg, Jonas,Lilja, Cristina
-
p. 1476 - 1478
(2007/10/02)
-