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61.
The stereoselective synthesis of 2-isoxazolidine through 1,3-dipolar cycloaddition reaction of nitrile oxide, which is in situ generation from aldoxime in the presence of N-bromosuccinamide and solid-supported reagent KF/Al2O3 at room temperature, is reported. KF/Al2O3 is sufficiently basic such that it can replace organic bases such as Et3N used in typical procedures and it catalyses the reaction to enhance the rate of the reaction.  相似文献   
62.
Cerium chloride heptahydrate proves to be an efficient catalyst for Michael addition of 1,3-dicarbonyl compounds, through a simple solvent free reaction under microwave irradiations.  相似文献   
63.
The preparation of steroid/nonsteroid fused 7-substituted pyrazolo[1,5-a]pyrimidines is described by a one-pot reaction of steroidal/nonsteroidal ketones, aromatic aldehydes and 3-amino-1H-pyrazoles/5-amino-1H-pyrazoles in the presence of potassium tert-butoxide in good yield under reflux condition in ethanol.  相似文献   
64.
Properties of steady state ion sheath formed in front of a negatively biased metal plate under the influence of negative ions have been investigated in collisionless argon/SF6 plasma. This experiment is carried out at a fixed discharge voltage and fixed filament heating power. In this experiment, the decrement in plasma pre-sheath potential drop as well as positive ion drift velocity toward the plate is experimentally recorded in the presence of negative ions. It is also found that the plasma positive ion density and plasma electron temperature decrease in the presence of negative ions. These factors attribute to the decrease of ion current toward the plate. Hence the usual ion sheath expands. Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India.  相似文献   
65.
We find new partition identities arising from Ramanujan’s formulas of multipliers. Several of the identities are for overpartitions, overpartition pairs, and \(\ell \)-regular partitions.  相似文献   
66.
We demonstrate stimulated emission depletion (STED) microscopy implemented in a laser scanning confocal microscope using excitation light derived from supercontinuum generation in a microstructured optical fiber. Images with resolution improvement beyond the far-field diffraction limit in both the lateral and axial directions were acquired by scanning overlapped excitation and depletion beams in two dimensions using the flying spot scanner of a commercially available laser scanning confocal microscope. The spatial properties of the depletion beam were controlled holographically using a programmable spatial light modulator, which can rapidly change between different STED imaging modes and also compensate for aberrations in the optical path. STED fluorescence lifetime imaging microscopy is demonstrated through the use of time-correlated single photon counting.  相似文献   
67.
We introduce the notion of fully Hilbertian fields, a strictly stronger notion than that of Hilbertian fields. We show that this class of fields exhibits the same good behavior as Hilbertian fields, but for fields of uncountable cardinality, is more natural than the notion of Hilbertian fields. In particular, we show it can be used to achieve stronger Galois theoretic results. Our proofs also provide a step toward the so-called Jarden-Lubotzky twinning principle.  相似文献   
68.
Herein,a protocol for the chemoselective formation of C−N bond using Cu(OTf)2 as catalyst has been described using heterocyclic thiones. The reaction occurs preferentially at the nitrogen centre over the sulphur atom leading to C−N bond formation. Water being the only by-product, the reaction is environmentally friendly. The reaction proceeds without any additive, ligand or inert atmosphere and shows good tolerance towards variety of alcohols and thiotetrazole derivatives. Our developed protocol could be scaled up to gram scale efficiently, which highlights the efficacy of this method and might offer potential application in synthetic industry.  相似文献   
69.
The steroidal and nonsteroidal 5-methyl pyrazolo[1,5-a]pyrimidines were synthesized by the reaction of steroidal/nonsteroidal α,β-unsaturated ketones and 3-amino-1H-pyrazoles/5-amino-1H-pyrazoles in the presence of KOtBu in ethanol under reflux condition.  相似文献   
70.
A novel I2-DMSO-mediated cascade cyclization approach for synthesizing 2-hydroxy-pyrrol-3(2H)-one scaffold from readily accessible β-ketosulfoxonium ylides and β-enaminone derivatives has been developed. Under metal-free and mild conditions, this cascade transformation facilitates the formation of one C−C bond and one C−N bond in a single reaction vessel, exhibiting a wide range of functional group compatibility. In addition, this method added an active hydroxyl group to a quaternary carbon center.  相似文献   
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