Oligonucleotide Analogues with Integrated Bases and Backbone. Part 14

The self‐complementary tetrameric propargyl triols 8, 14, 18 , and 21 were synthesized to investigate the duplex formation of self‐complementary, ethynylene‐linked UUAA, AAUU, UAUA, and AUAU analogues with integrated bases and backbone (ONIBs). The linear synthesis is based on repetitive Sonogashira couplings and C‐desilylations (34–72% yield), starting from the monomeric propargyl alcohols 9 and 15 and the iodinated nucleosides 3, 7, 11 , and 13 . Strongly persistent intramolecular H‐bonds from the propargylic OH groups to N(3) of the adenosine units prevent the gg‐type orientation of the ethynyl groups at C(5′). As such, an orientation is required for the formation of cyclic duplexes, this H‐bond prevents the formation of duplexes connected by all four base pairs. However, the central units of the UAUA and AAUU analogues 18 and 14 associate in CDCl₃/(D₆)DMSO 10 : 1 to form a cyclic duplex characterized by reverse Hoogsteen base pairing. The UUAA tetramer 8 forms a cyclic UU homoduplex, while the AUAU tetramer 21 forms only linear associates. Duplex formation of the O‐silylated UUAA and AAUU tetramers is no longer prevented. The self‐complementary UUAA tetramer 22 forms Watson–Crick‐ and Hoogsteen‐type base‐paired cyclic duplexes more readily than the sequence‐isomeric AAUU tetramer 23 , further illustrating the sequence selectivity of duplex formation.     

Synthesis,structure, and magnetic properties of the cobalt(<Emphasis Type="SmallCaps">II</Emphasis>) 1,3,5-benzenetricarboxylate layered coordination polymer

The reaction of Co(NO₃)₂·6H₂O with 1,3,5-benzenetricarboxylic acid (H₃btc, trimesic acid) in DMF at 100 °C afforded the coordination polymer [Co₃(dmf)₆(btc)(Hbtc)(H₂btc)]··9H₂O (1) (dmf is N,N′-dimethylformamide, DMF). According to the X-ray diffraction study, the metal-organic coordination polymer is composed of planar honeycomb (6,3) networks, in which the organic benzenetricarboxylate anions and the inorganic Co²⁺ cations play a role of three-connected nodes. Disordered water molecules are intercalated between the layers. A study of the magnetic properties showed the presence of a weak antiferromagnetic coupling between the Co²⁺ ions (S = 3/2). Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1719–1723, September, 2007.     

A concise and efficient synthesis of salvinal from isoeugenol via a phenoxenium ion intermediate

In this letter, we describe how salvinal can be efficiently synthesized from isoeugenol via a phenoxenium ion intermediate by four steps in 23% over all total yield.     

金属键有机化合物的研究——η~5-取代环戊二烯基三羰基钼(钨)二聚体的合成

通过Fe_2(SO_4)_3醋酸水溶液与η~5-取代环戊二烯基三羰基钼(钨)的钠盐或锂盐(η~5-RC_5-H_4)(CO)_3MNa(Li)之间的相互作用,合成了9个η~5-取代环戊二烯基三羰基钼(钨)二聚体[(η~5-RC_5H_4)(CO)_3M]_2(M=Mo,W; R=C(O)Me,CO_2Me,CO_2Et,n-Bu,Me_3Si),并用C/H分析,IR、~1H NMR及MS表征了它们的结构.     

Ab initio study of the NMR shielding constants and spin-spin coupling constants in cyclopropene

Summary Ab initio calculations of parameters which characterize the NMR spectrum are presented for the cyclopropene molecule. The London orbitals CHF (or GIAO-CHF, Gauge-Independent Atomic Orbital Coupled Hartree-Fock) results for the shielding constants are in good agreement with the experimental data, accurately determined, and with otherab initio values. The calculations of the NMR spin-spin coupling constants have been performed using the Multiconfiguration Time-Dependent Hartree-Fock (MC TDHF) approach. Different basis sets and MC SCF wavefunctions were used to estimate the accuracy of the results. Good agreement is obtained with the coupling constants estimated using the available experimental data.Dedicated to Professor Werner Kutzelnigg on the occasion of his 60th birthday     

Synthesis and properties of N-carbazole end-capped conjugated molecules

A series of novel N-carbazole end-capped π-conjugated molecules were synthesized by a divergent approach with the use of bromination, Suzuki cross-coupling, and Ullmann reactions and their physical properties were investigated. In dilute solution, UV-vis absorption spectra displayed bathochromic shift with respect to their conjugated backbones, and photoluminescence spectra showed emission maxima in the blue region. Thermal analysis revealed that they are thermally stable semi-crystalline and amorphous materials. All molecules exhibited good electrochemical stability with high-lying HOMO energy levels and have potential applications as hole-transporting and light-emitting layers in organic light-emitting diodes or as host materials for electrophosphorescent applications.     

Novel bifluorene based conjugated systems: synthesis and properties

A series of novel bifluorene based systems was synthesised by a convergent approach by means of a Suzuki cross-coupling between 7,7′-bis-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-9,9,9′,9′-tetraoctyl-2,2′-bifluorene and suitable aryl-bromides. All the oligomers have been characterized by ¹H, ¹³C NMR, FT-IR, UV-vis, PL spectroscopy and mass analyses. In particular, it has been demonstrated that the presence of strong electron donor (amines) or withdrawing (carboxylic esters) groups causes a bathochromic shift of the optical properties with respect to those of unsubstituted molecules. The effects of these functional groups on the HOMO-LUMO energy levels were investigated by cyclic voltammetry. Remarkably, the LUMO energy level of 7,7′-bis-[5′-carbodecaoxy-2,2′-bithiophen-5-yl]-9,9,9′,9′-tetraoctyl-2,2′-bifluorene (−3.07 eV) is strongly influenced by the presence of the ester functional group.     

Theoretical prediction of the contact distance dependence of the electron transfer reactivity of the ClO/ClO− coupling system

On the basis of the structures and properties of the ClO/ClO^? system obtained at the density functional theory (DFT) (UB3LYP) level, employing the 6‐311+G(3df) standard basis set, the electron transfer reactivity of this system is investigated. The results indicate that there are five possible stable coupling complexes that correspond to the generous minima on the global potential energy surfaces (PES). The most stable coupling complex is planar EC4, in which there is a O? O linkage with two trans‐Cl atoms. Their stabilization energies are calculated to be 20.57 (EC1: C₁), 20.54 (EC2: C₂, ²B), 20.69 (EC3: C₁), 20.70 (EC4: C_s, ²A′), and 20.69 (EC.5: C_2h, ²B_u) kcal/mol at the B3LYP/6‐311+G(3df) level; with the correction of the basis set superposition error (BSSE), the stability order of these encounter complexes is EC4 > EC.5 > EC3 > EC1 > EC2. Based on the five encounter complexes, five coupling modes are designed for the study of the electron transfer reactivity of this system. The dissociation energy curves at the activated states and the corresponding activation energies of these five coupling modes are obtained and are compared at the B3LYP/6‐311+G(3df) and MP2/6‐311+G* levels. The inapplicability of DFT methods has also been discussed in this article in predicting the energy curves, especially with a long contact distance, in which DFT methods give the abnormal behavior for the dissociations of the complexes caused by the “inverse symmetry breaking” problem. On the basis of the golden rule of the time‐dependent perturbation theory, the electron transfer reactivity and the contact distance dependence of the various electron transfer kinetics parameters (e.g., activation energy, coupling matrix element) have been analyzed at the UMP2(full)/6‐311+G* level. The electron transfer can take place over a range of contact distances, but the most effective coupling distance corresponds to only a small range. The coupling orientation analyses also indicate that the most favorable coupling mode to the electron transfer does not always correspond to the most stable encounter complex mechanism. Some highly energetic coupling modes are more favorable for the electron transfer. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Total Synthesis of Several 8, 8",-Biflavones

8,8"-Biflavonoidsareantw0rtantclass0fbiflavonoids.Asasystematicresearchofthe8,8"-biflav0noids,wehavepreviouslyreportedthestudyonthereactionof2'-hydroxychaloneswithl2-H2SO4-DMSOsystem.'InthispaPer,thesynthesisof5,5",7,7',-tetTameth0xy-8,8"-biflavonela2,4,4",7,7"-tetramethoxy-8,8"-biflavone1b',4',4",,5,5,',7,7"-hexamethoxy-8,8"-biflav0ne1c4and4,4"-dibenZyl0xy-5,5",7,7"-tetramothoxy-8,8"-biflavoneldisreported.ThesyntheticmethodisshownintheSchemebelow.2-Hydroxyacet0phenonescondensedwithsubsti…     

Use of tetrahydropyrimidinium salts for highly efficient palladium-catalyzed cross-coupling reactions of aryl bromides and chlorides

New, sterically demanding 1,3-dialkyl-3,4,5,6-tetrahydropyrimidinium salts (2) as NHC precursors have been synthesized and characterized. These salts, in combination with palladium acetate, provided active catalysts for the cross-coupling of aryl chlorides and bromides under mild conditions. The catalytic system was applied to the Heck, Suzuki and benzaldehyde (Kumada) coupling reactions. Catalyst activity was found to be influenced by the presence of a methoxy group on the ring of the p-position of benzyl substituent of the ligand precursor.