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51.
Intermolecular additive free microwave (MW) promoted and cobalt octacarbonyl mediated Pauson-Khand reaction (PKR) performance was improved for estrone ring extension. The reaction development with norbornene and cyclopentene produced cyclopentenones in yields of comparable levels with those previously obtained with the aid of chemical additives as promoters. The PKRs with norbornene demonstrated that a low cobalt complex concentration increases yields, especially for the aliphatic alkynes. Furthermore, a boost for the MW PKR could be obtained by a gradual cobalt complex addition. These expedients combined with the use of an excess of free and cobalt complexed alkyne led to successful estrone ring system extension with various alkynes. 相似文献
52.
Zhang W Bah J Wohlfarth A Franzén J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(49):13814-13824
Here we present a general and common catalytic asymmetric strategy for the total and formal synthesis of a broad number of optically active natural products from the corynantheine and ipecac alkaloid families, for example, indolo[2,3-a]- and benzo[a]quinolizidines. Construction of the core alkaloid skeletons with the correct absolute and relative stereochemistry relies on an enantioselective and diastereodivergent one-pot cascade sequence followed by an additional diastereodivergent reaction step. This allows for enantio- and diastereoselective synthesis of three out of four possible epimers of the quinolizidine alkaloids that begin from common and easily accessible starting materials by using a common synthetic route. Focus has been made on excluding protecting groups and limiting isolation and purification of synthetic intermediates. This methodology is applied in the total synthesis of the natural products (-)-dihydrocorynantheol, (-)-hirsutinol, (-)-corynantheol, (-)-protometinol, (-)-dihydrocorynantheal, (-)-corynantheal, (-)-protoemetine, (-)-(15S)-hydroxydihydrocorynantheol, and an array of their nonnatural epimers. The potential of this strategy is also demonstrated in the synthesis of biologically interesting natural product analogues not accessible through synthetic elaboration of alkaloid precursors available from nature, for example, thieno[3,2-a]quinolizidine derivatives. We also report the formal synthesis of (+)-dihydrocorynantheine, (-)-emetine, (-)-cephaeline, (-)-tubulosine, and (-)-deoxytubulosine. 相似文献
53.
Filippov V Chamorovskii Y Kerttula J Kholodkov A Okhotnikov OG 《Optics letters》2008,33(13):1416-1418
With a tapered double-clad all-glass ytterbium fiber as a gain medium, a maximum output power of over 200 W at 1079 nm and a slope efficiency of over 70% were demonstrated. The tapered double-clad fiber concept allows for using low-brightness diode bars and results in cost-effective and efficient high-power fiber lasers. The adiabatic conical fiber gain waveguide combines improved pump absorption owing to enhanced mode mixing in the pump cladding, low-noise single fundamental mode operation with M(2)< or =1.02, and strong potential for significant power scaling. 相似文献
54.
Välikangas Juho Laine Petteri Hietaniemi Marianna Hu Tao Selent Marcin Tynjälä Pekka Lassi Ulla 《Journal of Solid State Electrochemistry》2023,27(3):641-654
Journal of Solid State Electrochemistry - This article presents a process for producing LiNi1-xAlxO2 (0 < × < 0.05) cathode material with... 相似文献