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The reversibly formed C?N bond plays a very important role in dynamic covalent chemistry and the C?N/C?N exchange of components between different imine constituents to create dynamic covalent libraries has been extensively used. To facilitate diversity generation, we have investigated an organocatalyzed approach, using L ‐proline as catalyst, to accelerate the formation of dynamic libraries of [n×n] imine components. The organocatalysis methodology has also been extended, under somewhat modified conditions, to reversible C?C/C?N exchange processes between Knoevenagel derivatives of barbituric acid and imines, allowing for the generation of increased diversity. 相似文献
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Organocatalyzed and Uncatalyzed CC/CC and CC/CN Exchange Processes between Knoevenagel and Imine Compounds in Dynamic Covalent Chemistry 下载免费PDF全文
Molecular diversity generation through reversible component exchange has acquired great importance in the last decade with the development of dynamic covalent chemistry. We explore here the recombination of components linked by C?C and C?N bonds through reversible double‐bond formation, and cleavage in C?C/C?C and C?C/C?N exchange processes. The reversibility of the Knoevenagel reaction has been explored, and C?C/C?C C/C exchanges have been achieved among different benzylidenes, under organocatalysis by secondary amines such as L ‐proline. The substituents of these benzylidenes were shown to play a very important role in the kinetics of the exchange reactions. L ‐Proline is also used to catalyze the reversible C?C/C?C exchange between Knoevenagel derivatives of barbituric acid and malononitrile. Finally, the interconversion between Knoevenagel derivatives of dimethylbarbituric acid and imines (C?C/C?N exchange) has been studied and was found to occur rapidly in the absence of catalyst. The results of this study pave the way for the extension of dynamic combinatorial chemistry based on C?C/C?C and C?C/C?N exchange systems. 相似文献
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Novel structures of H2C?C?CLiX (X ? F, Cl) were determined using HF/STO-3G gradient method. Both of the carbenoids have two equilibrium structures, askew and linear forms, at the level of calculation. In the case X?F, the former is more stable, but in the case X=Cl, the latter is more stable. The frontier MOs are given and analyzed. 相似文献
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Helmut Poleschner Reiner Radeglia Hinrich Meyer 《Magnetic resonance in chemistry : MRC》1984,22(8):480-485
This paper reports the 77Se NMR chemical shifts of 1,3-dithiole-, 1,3-thiaselenole- and 1,3-diselenole-2-ones, -thiones and -selones, of the corresponding saturated compounds 1,3-diselenolane-2-one, -thione and -selone, and the 1,3-thiaselenolium tetrafluoroborates, either unsubstituted or substituted by morpholino, ethylthio or ethylseleno groups in the 2-position. The 77Se chemical shift values of the ring selenium and the C?Se groups are compared with the 13C chemical shift values of neighbouring carbon atoms. The relationships between the 77Se chemical shifts of the C?Se groups and the wavelengths of their n→* absorption in the UV-visible spectrum are discussed with respect to the significance of the δE term in the contribution of the paramagnetic screening and the electron density distribution. 相似文献
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《Journal of mass spectrometry : JMS》2005,40(6):796-806
Dissociative electron ionization (70eV) of selenophene (C4H4Se) generates m/z 106 ions of composition [H2, C2, 80Se]+? and m/z 105 ions of [H, C2, 80Se]+. From tandem mass spectrometric experiments, Density Functional Theory (DFT) and ab initio calculations, it is concluded that these ions have the structure of selenoketene H2C?C?Se+? (1a+? )and selenoketyl HC?C?Se+ (2a+) ions respectively. The calculations predict that selenoketene ion 1a+? is separated by high energy barriers from its isomers selenirene (H e)+? 1b+?, ethyne selenol (HCCSeH)+? 1c+?, (CCHSeH)+? 1d+? and (CCSeH2)+? 1e+?. The selenoketyl ion 2a+ is separated by high barriers from its isomers (CCHSe)+ 2b+, and (CCSeH)+ 2c+. Neutralization‐reionization mass spectra (NRMS) of these structurally characterized ions confirmed that the corresponding neutral analogues, selenoketene H2CCSe 1a and selenoketyl radical HCCSe 2a? are stable in the rarefied gas phase. The relative, dissociation, and isomerization energies for selenoketene and selenoketyl ions and neutrals studied at B3LYP/6–31G(d,p) and G2/G2(MP2) levels are used to support and interpret the experimental results. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Metal Alkoxide Promoted Regio‐ and Stereoselective CO and CC Metathesis of Allenoates with Aldehydes 下载免费PDF全文
Minyan Wang Dr. Zhao Fang Prof. Dr. Chunling Fu Prof. Dr. Shengming Ma 《Angewandte Chemie (International ed. in English)》2014,53(12):3214-3217
The reaction of 2,3‐allenoates and aldehydes in the presence of an alkoxide affords alkyl 4,5‐diaryl‐3‐oxo‐2‐propylpent‐4(E)‐enoates and cis‐3,4‐diaryloxetanes through a formal C?O and C?C metathesis. A mechanism for this reaction has been proposed. 相似文献
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