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121.
A mild and improved method for the synthesis of thioethers has been developed. In the presence of cesium carbonate, tetrabutylammonium iodide, and DMF, various alkyl and aryl thiols underwent S-alkylation to afford structurally diverse sulfides in high yield. Unprotected mercaptoalcohols and thioamines reacted chemoselectively at the sulfur moiety exclusively. An example of a one-pot, solid-phase synthesis of a thioether is also described.  相似文献   
122.
123.
Chromium(II) salts can be used for a variety of reductions in organic chemistry; for example, alkyl halides and suitably substituted olefins may both be reduced to alkanes, and alkynes may be converted into trans-olefins. Several epoxyketones are reduced to α,β-unsaturated ketones or β-hydroxyketones, and a nitro steroid was found to give a hydroxy(hydroxyimino) compound. The reduction of alkyl halides is reported to proceed by a free-radical mechanism; the halogen atom that is set free forms a bridge between two chromium atoms.  相似文献   
124.
Abstract

Pulsed NMR determinations of the relaxation times T2, T2* and T1, as a function of temperature and field, for the methyl group protons in (TMTSF)2PF6 are reported. Below the metal-insulator transition (TMI)T2* shortens while T2 increases, indicating a line which is inhomogeneously broadened due to the onset of a SDW. The SDW also contributes to the spin-lattice relaxation rate, T1 ?1, in the neighborhood of TMI. A frequency dependent maximum in T1 ?1 is observed near 20K and is attributed to methyl group rotation. A frequency independent maximum at 58K suggests a structural phase transition involving rearrangement of the methyl and PF6 groups.  相似文献   
125.
Two-photon resonant four-wave mixing spectroscopy has been utilized successfully for probing I and I nascent from the 266 nm photodissociations of various alkyl and perfluoroalkyl iodides. The relative quantum yields for I, as well as the recoil anisotropy parameters, were extracted. Recoil anisotropy parameters close to the limit value for parallel transition indicates that the ground-state I(2P3/2) originates from the curve crossing from the initially prepared 3Q0 to 1Q1 state. The curve-crossing probabilities for alkyl and perfluoroalkyl iodides were obtained and tried to explain using the well-known Landau-Zener model. In the cases of perfluoroalkyl iodides, it is necessary to consider the fluorination effect to describe the detailed dynamics observed in this study and has been revealed that the electronic effect due to fluorine atom substitution is dominant, leading to decrease in the curve-crossing probability.  相似文献   
126.
Neelamegam Ramesh 《Tetrahedron》2008,64(9):2071-2079
A detailed study on the interaction of N-protected bromomethylindoles with various types of aryl/alkyl Grignard is reported. Full experimental details on the mechanism of the unusual dimerization reaction are presented.  相似文献   
127.
A facile and highly efficient nucleophilic (phenylthio)difluoromethylation of alkyl halides has been achieved via fluoride ion-mediated substitution reaction using [difluoro(phenylthio)methyl]trimethylsilane (Me3SiCF2SPh). The reaction proceeds well with primary alkyl bromides (or alkyl iodides) in DME solvent when CsF/15-crown-5 was used as the fluoride source/additive. The PhSCF2-containing products can be readily transformed into CF2H-containing compounds via a free-radical desulfurization method.  相似文献   
128.
A new method for the synthesis of di‐ and trisubstituted pyrroles via copper‐catalyzed cyclization of ethyl allenoates with activated isocyanides has been developed. In contrast to related annulation reactions previously reported, this new process features a skeletal rearrangement in which the aryl sulfonyl moiety, which functions as the electron‐withdrawing group in the α‐carbon of the isocyanide, was found to migrate to the γ‐carbon of the starting allenoate in the final product for the first time.  相似文献   
129.
The frequency response characteristics for twenty-two organic vapours by piezoelectric thickness-shear-mode (TSM) acoustic wave sensors coated with four supramolecule compounds—calixarenes have been investigated. Among them, 2,8,14,20-tetraethyl-4,6,10,12,16,18,22,24-octahydroxylcalix[4]arene (I) was the most efficient actively adsorptive material for host-guest recognizing alkyl ketone molecules such as 2-butanone and acetone. The supramolecule recognition mechanism has been discussed, that is based on the formation of C-H?π bond interaction between the methyl group of ketone molecule and the phenyl ring of the calixarene compound. The linear range of the TSM sensor upon exposure to 2-butanone vapour was 0-940.5 ppm with a detection limit of 2.67 ppm when the coating mass of the compound I was selected as 19 μg. The kinetics behaviours in the adsorption and desorption processes have been examined with polynomial curve fitting procedure. Furthermore, the proposed TSM sensor possessed good selectivity, reversibility, reproducibility and high stability. Compared with gas chromatography (GC) method, the proposed sensor can be used for on-line determination of 2-butanone vapour in air with a recovery of 94.8-106.5%, which was in consistent with those obtained by GC method.  相似文献   
130.
Rate constants directly measured from GC-analyzed method for SmI2 reduction of alkyl halides were obtained. The rates increase in the orders of primary, secondary, tertiary RX and RCl < RBr < RI as expected. 2-Heptanone was chosen as the partner of alkyl halide in the samarium Barbier reaction. In the absence of HMPA, the reaction orders of alkyl halide and ketone were determined as first and zero order, respectively.  相似文献   
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