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931.
932.
933.
An Alkene‐Promoted Borane‐Catalyzed Highly Stereoselective Hydrogenation of Alkynes to Give Z‐ and E‐Alkenes
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Dr. Yongbing Liu Lianrui Hu Prof. Dr. Hui Chen Prof. Dr. Haifeng Du 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3495-3501
The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ and E‐alkenes by the same catalytic hydrogenation system using molecular H2 has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C6F5)2‐catalyzed metal‐free hydrogenation of alkynes was adopted. Significantly, both Z‐ and E‐alkenes can be furnished by hydrogenation with molecular H2 in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H2 play an essential role in promoting the hydrogenolysis reaction. 相似文献
934.
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936.
Guifang Ju Yihua Hu Li Chen Xiaojuan Wang Lihua Hung 《Applied Physics A: Materials Science & Processing》2014,114(3):867-874
We investigate the persistent luminescence in europium-doped SrMg2(PO4)2 upon codoping with auxiliary terbium. Luminescence properties of the phosphors, including photoluminescence, luminescence decay and thermoluminescence, are systematically studied. SrMg2(PO4)2:Eu2+ shows only a weak persistent luminescence, and codoping with Tb3+ is necessary to obtain considerable persistent luminescence. An energy level scheme is constructed to convey reasonable trapping and detrapping processes in the material. 相似文献
937.
938.
We consider a ruin model with random income and dependence between claim sizes and claim intervals. In this paper, we extend the determinate premium income into a compound Poisson process and assume that the distribution of the time between two claim occurrences depends on the previous claim size.Given the premium size is exponentially distributed, the(Gerber-Shiu) discounted penalty functions is derived.Finally, we consider a similar model. 相似文献
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940.
Cong-De Huo Xia-Zhen Bao Dong-Cheng Hu Xiao-Dong Jia Chou-Gu Sun Cheng Wang 《中国化学快报》2014,25(5):699-701
A solid complex,readily prepared from commercially available sodium triphenylphosphine-m-sulfonate(TPPMS) and carbon tetrabromide,can be used as an easily recoverable and reusable catalyst system for one-pot condensation of 2-naphthol with aldehydes to construct 14-aryl(alkyl)-14H-dibenzo[a j]-xanthene derivatives and one-pot condensation of 2-naphthol with aldehydes and cyclic 1 3-dicarbonyl compounds to construct 12-aryl(alkyl)-8 9 10 12-tetrahydrobenzo[a]xanthen-11-one derivatives. 相似文献