Synthesis of 4″-benzyloxyimino-4″-deoxyavermectin Bla derivatives

Six new 4″-benzyloxyimino-4″-deoxyavermectin Bla derivatives were synthesized from avermectin Bla by the selective protection of C-5-hydroxy group,oxidation of C-4″-hydroxy group,and deprotection followed by reaction with O-substituted hydroxylamine hydrochlorides.Their structures were confirmed by IR,~1H NMR,~(13)C NMR and MS.Insecticidal activities of the derivatives against Phopalosiphum pseudobrassicae,Spodoptera exigua and Pluteua xylosteua were evaluated.     

电化学检测在流动注射分析中的应用

评述了近几年来电化学检测在流动注射分析中的应用，展望了流动注射电化学分析法的发展动向。     

Kinetics of the thermal unimolecular decomposition of hex-1-ene-3-yne. Heat of formation and resonance stabilization energy of the 3-ethenylpropargyl radical

The thermal unimolecular decomposition of hex-1-ene-3-yne (HEY) has been investigated over the temperature range 949–1230 K using the technique of very low-pressure pyrolysis (VLPP). One reaction pathway is the expected C₅? C₆ bond fission to form the resonance-stabilized 3-ethenylpropargyl radical. There is a concurrent process producing molecular hydrogen which probably occurs via the intermediate formation of hexatrienes and cyclohexa-1,3-diene. RRKM calculations yield the extrapolated high-pressure rate parameters at 1100 K given by the expressions 10^16.0±0.3 exp(?300.4 ± 12.6 kJ mol^?1/RT) s^?1 for bond fission and 10^13.2+0.4 exp(?247.7 ± 8.4 kJ mol^?1/RT) for the overall formation of hydrogen. The A factors were assigned from the results of previous studies of related alkynes, alkenes, and alkadienes. The activation energy for the bond fission reaction leads to ΔH [H₂CCHCC?H₂] = 391.9, DH [H₂CCHCCCH₂? H] = 363.3, and a resonance stabilization energy of 56.9 ± 14.0 kJ mol^?1 for the 3-ethenylpropargyl radical, based on a value of 420.2 kJ mol^?1 for the primary C? H bond dissociation energy in alkanes. Comparison with the revised value of 46.6 kJ mol^?1 for the resonance energy of the unsubstituted propargyl radical indicates that the ethenyl substituent (CH₂?CH) on the terminal carbon atom has only a small effect on the propargyl resonance energy. © John Wiley & Sons, Inc.     

Palladium-catalyzed tandem cyclization/Suzuki coupling of 1,6-enynes: reaction scope and mechanism

A palldium(0)-catalyzed tandem cyclization/Suzuki coupling reaction of various 1,6-enyne substrates was developed. This Pd-catalyzed enyne cyclization reaction represents a new process for the synthesis of stereodefined alpha-arylmethylene-gamma-butyrolactones, lactams, multifunctional tetrahydrofurans, pyrrolidines, and cyclopentanes. The mechanism of the reaction was studied by the employment of different enyne isomers and boronic acids; a pi-allyl palladium intermediate was suggested to explain the formation of the cyclic products. The stereochemistry of this reaction can be well explained by a chairlike transition state.     

Crystal Structures and Magnetic Studies of Naphthalene Derivatives Containing Nitronly Nitroxides

Crystal structures of new nitronyl nitroxide derivatives 1, 2 and 3 were determined with X‐ray diffraction analysis: 1, monoclinic, C₂/c, a = 1.2404(5) nm, b = 0.9730(5) um, c = 2.7049(10) ran, β = 98.189(15)°, V = 3.2315(24) nm³, Z = 8; 2, or‐thorhombic, Pbca, a = 0.61262(2) nm, b = 1.11426(6) nm, c = 2.30543(13) nm, V = 1.57373(13) nm³, Z = 4; 3, monoclinic, P2(1)/n, a=0.64253(4) nm, b=2.55003(17) nm, c = 1.15497(6) nm, β = 95.000(3)°, V = 1.8852(2) nm³, Z = 4. Their magnetic properties were measured with SQUID and analyzed based on their crystal structures with simple singlet‐triplet, modified one dimensional antiferromagnetic chain and modified singlet‐triplet models respectively: 1, J/k_b= ?2.5 K; 2, J/k_b = 7.8 K, θ = 2.8 K; 3, J/k_b = ?0.96 K, θ = 0.21 K.     

Application of a new standardization method in activation analysis with registration of soft gamma radiation

An application of a new standardization method for rapid activation mass analysis with registration of the strongly absorbed low-energy gamma radiation is described. This method makes it possible to avoid the use of the time-consuming and laborious method of Internal Standard.     

Oligothiophene isocyanides for platinum-based molecular electronic applications

Understanding molecular orientation on a metal surface is key to designing molecular electronic device junctions. Though platinum device electrodes are of particular interest as a more stable alternative to the often used gold electrodes, the chemisorption of conducting molecules onto platinum surfaces has not been thoroughly studied. We present herein the first detailed study of the ability and manner in which soluble oligothiophene isocyanides, of lengths ranging from 2 to 7 nm, chemisorb onto platinum surfaces and nanoparticles. It was found that these oligothiophene isocyanides stand at a 41 degrees angle from the platinum surface normal, suggesting their applicability in molecule-bridged platinum electrode devices.     

From model compounds to extended pi-conjugated systems: synthesis and properties of dithieno[3,2-b:2',3'-d]phospholes

To explore their suitability for applications in molecular optoelectronics and as sensory materials, novel dithieno[3,2-b:2',3'-d]phospholes have been synthesized and their reactivity and properties investigated. An efficient two-step synthesis allowed for a modular assembly of differently functionalized compounds. The dithieno[3,2-b:2',3'-d]phosphole system exhibits extraordinary optoelectronic properties with respect to wavelength, intensity, and tunability. Owing to the nucleophilic nature of the central phosphorus atom, its significant electronic influence on the conjugated pi system can be altered selectively by chemically facile modifications such as oxidation or complexation with Lewis acids or transition metals. All the dithienophosphole species presented show very strong blue photoluminescence with excellent quantum yield efficiencies supporting their potential utility as blue-light emitting components in organic light emitting diodes (OLEDs). Furthermore, depending on the electronic nature of the phosphorus center, the materials exhibit distinctive optoelectronic properties suggesting that the dithieno[3,2-b:2',3'-d]phosphole system may be useful as sensory material. Theoretical calculations, including time-dependent DFT methods, revealed the excellent predictability of the structures and optoelectronic properties of the functionalized dithienophospholes allowing the design of future dithieno[3,2-b:2',3'-d]phosphole-based materials to be "stream-lined". By using tin-functionalized dithienophosphole monomers, a strategy, which involves Stille coupling, towards extended pi-conjugated materials with significantly redshifted optoelectronic properties is also presented.     

Domino "[3+3]-cyclization-homo-Michael" reactions of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes

The Lewis acid mediated domino "[3+3]-cyclization-homo-Michael" reaction of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes allows an efficient one-pot synthesis of functionalized salicylates containing a halogenated side chain. A great variety of substitution patterns could be realized by variation of the starting materials and of the Lewis acid. The mechanism of the domino process was studied.