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排序方式: 共有126条查询结果,搜索用时 15 毫秒
1.
2.
A new method for the preparation of the synthon (±)-2,6,7,7a-tetrahydro-1β-hydroxy-4-formyl-7aβ-methylindene (1,a) for the
total synthesis of steroids in both (±) and (+) forms, starting from the known β-ketoester, (±)-methyl 1β-t-butoxy-5,6,7,7a-tetrahydro-7aβ-methyl-5-keto-4-indancarboxylate (2,a) has been described. An alternative route to (1,a) has
been investigated. Although the compound, (±)-1β-hydroxy-5,6,7,7a-tetrahydro-7aβ-methyl-5-keto-4-methoxymethylindan (2,b)
could not be prepared, interesting pathways leading to two unexpected products, (±)-5,6,7,7a-tetrahydro-4,7a-dimethyl-5H-indene-1,5-dione
and (±)-2,6-diketo-3-methyltricyclo-(5,2,1,0)decan-8-ol (3 and 4), were encountered during an attempted annelation reaction
of the ketone, N-diethylamino-5-methoxypentan-3-one (6), with 2-methylcyclopentan-1,3-dione (5). Trapping of the intermediate,
(±)-3a,4,5,6,7,7a-hexahydro-3a-hydroxy-4-methylene-7a-methylindene-1,5-dione (7), through the formation of the adduct, (±)-3a,4,5,6,7,7a-hexahydro-3a-hydroxy-4-(1′,
3′-diketo-2′-methylcyclopentano-2′-methylene)-7a-methylindene-1,5-dione (8), established the mechanism of the formation of
the products (3 and 4). 相似文献
3.
The structure of the abnormal product 1a formed in the Knoevenagel condensation of 2-carbethoxycyclohexanone and malononitrile has been further confirmed. Oxidation of the tetrahydroisoquinoline 3b using Na2Cr2O-AcOH-H2SO4 gave the keto isoquinoline 3d and the isoquinoline-1-carboxylic acid 5a. The acid chloride of 5a was condensed with diethyl ethoxymagnesiomalonate to afford after decarbethoxylation the methyl ketone 5d which on Baeyer-Villiger oxidation gave a mixture of the acetate 1g and the title compound 1b. The unambiguous synthesis of 1b confirms the structure assigned earlier to the title compound also formed during the partial hydrolysis of the diethoxy compound 1c. Condensation of 2-acetylcyclohexane-1,3-dione with malononitrile gave the quinoline derivative 4c which on ethylation yielded the ketoquinoline 4d. The present studies have confirmed that the quinoline compound 4a is also formed in the condensation of 2-acetylcyclohexanone and cyanoacetamide. 相似文献
4.
5.
Vibrational dephasing of the nitrogen molecule is known to show highly interesting anomalies near its gas-liquid critical point. Here we present theoretical and computational studies of the Raman linewidth of nitrogen along the critical isochore. The linewidth is found to have a lambda-shaped temperature dependence near the critical point. As observed in experimental studies, the calculated line shape becomes Gaussian as the critical temperature (T(c)) is approached. Both the present simulation and a mode coupling theory analysis show that the slow decay of the enhanced density fluctuations near the critical point, probed at the subpicosecond time scales by vibrational frequency modulation, along with an enhanced vibration-rotation coupling, are the main causes of the observed anomalies. 相似文献
6.
Expressions are derived for the spectrum of the field generated by a planar, homogeneous, secondary source of any spectral distribution and of any state of spatial coherence. It is shown that the state of coherence affects the contributions of the homogeneous as well as the evanescent waves of the emitted field. The near-field spectra are studied in detail. The analysis is illustrated by examples. 相似文献
7.
T. A. Dang H.‐J. Lunk S. Roychowdhury T. A. Frisk T. J. Bard 《Surface and interface analysis : SIA》2010,42(1):45-51
Solid standards prepared by freeze‐drying consistently showed a high degree of homogeneity. The freezing process, completed in fractions of a second, preserves the original homogeneous distribution of the dopants, and the subsequent sublimation step would minimize any disturbance. Compared to those prepared by conventional methods such as blending and spiking, freeze‐dried standards exhibited superior lateral distribution and better uniform depth distribution. There is, however, a concentration constraint for achieving homogeneity. At 5% doping, segregation was observed in both lateral and depth distribution. Many tungsten standards doped with 10–28 elements ranging from 10 to 200 ppm were successfully prepared and used as controls for a number of analytical techniques including glow discharge mass spectrometry (GDMS) and d.c.‐arc optical emission spectroscopy (OES). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
8.
Mrinal Kanti Roychowdhury 《Journal of Mathematical Analysis and Applications》2011,383(2):499-505
The quantization dimension function for a probability measure induced by a set of infinite contractive similarity mappings and a given probability vector is determined. A relationship between the quantization dimension function and the temperature function of the thermodynamic formalism arising in multifractal analysis is established. The result in this paper is an infinite extension of Graf and Luschgy [S. Graf, H. Luschgy, The quantization dimension of self-similar probabilities, Math. Nachr. 241 (2002) 103-109]. 相似文献
9.
Shalini Bagchi Kasturi Roychowdhury A.P. Mishra A. Roy Chowdhury 《Communications in Nonlinear Science & Numerical Simulation》2010,15(2):275-280
Excitation of nonlinear waves in a quantum dusty plasma with various effects is analyzed when the geometry is cylindrical.This introduces the effect of finite boundary conditions on the solitary waves so generated. it is observed that the nonlinear equation deduced is cylindrical KP–Burger type leading to the generation of Shock Wave. Different situations which arises in various parameter regions are considered separately and the form of the nonlinear excitations are obtained explicitly. 相似文献
10.
We show that any k-fold covering using translates of an arbitrary convex polygon can be decomposed into Ω(k) covers. Such a decomposition can be computed using an efficient (polynomial-time) algorithm. 相似文献