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1.
[structures: see text] The total syntheses of the amaryllidaceae alkaloids haemanthidine, pretazettine, and tazettine as optically pure enantiomers are reported. Using D-mannose as the starting material, the critical relative stereochemical relationships are established with an intramolecular nitrone-alkene cycloaddition reaction. The synthetic route leads successively to (-)-haemanthidine and then to (+)-pretazettine and (+)-tazettine, taking advantage of the well-established complex relationships among these three alkaloids. 相似文献
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[structure: see text] A new series of ligands with a novel phosphine-aminophosphine ligation design as depicted in structure 1 has been prepared on a ferrocenylethyl backbone. These BoPhoz ligands of structure 2 have afforded exceedingly high activity and enantioselectivity in the rhodium-catalyzed asymmetric hydrogenation of dehydro-alpha-amino acid derivatives, itaconic acids, and alpha-ketoesters. These air-stable ligands are readily prepared from cost-effective and non-pyrophoric intermediates. 相似文献
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H. Karami J. Carr N.C. Debenham D.A. Garbutt W.G. Jones D.M. Binnie J. Keyne P. Moissidis H.N. Sarma I. Siotis 《Nuclear Physics B》1979,154(3):503-518
Measurements are reported of the differential cross section for the reaction π?+p→ω+n from threshold to a final-state c.m. momentum . The previously reported fall in total cross section below about 100 MeV/c is again seen. The differential cross section remains close to isotropic over the entire range. A paralle experiment on the variation in the elastic differential cross section across the threshold shows evidence of this threshold. The elastic data cover a range of incident moments from 1010 to 1180 MeV/c in steps of 5 MeV/c. 相似文献
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In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed. 相似文献
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A. Ertoprak B. Cederwall C. Qi M. Doncel U. Jakobsson B. M. Nyakó G. Jaworski P. Davies G. de France I. Kuti D. R. Napoli R. Wadsworth S. S. Ghugre R. Raut B. Akkus H. Al Azri A. Algora G. de Angelis A. Atac T. Bäck A. Boso E. Clément D. M. Debenham Zs. Dombrádi S. Ertürk A. Gadea F. Ghazi Moradi A. Gottardo T. Hüyük E. Ideguchi H. Li C. Michelagnoli V. Modamio J. Nyberg M. Palacz C. M. Petrache F. Recchia M. Sandzelius M. Siciliano J. Timár J. J. Valiente-Dobón Z. G. Xiao 《The European Physical Journal A - Hadrons and Nuclei》2018,54(9):145
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Boaz NW Mackenzie EB Debenham SD Large SE Ponasik JA 《The Journal of organic chemistry》2005,70(5):1872-1880
A new class of bidentate ligands utilizing a phosphine-aminophosphine structure has been prepared on a ferrocenylethyl backbone in a straightforward and scalable fashion from acetylferrocene. The unique property of the alpha-ferrocenyl carbonium ion that allows the replacement of a variety of "leaving groups" with retention of configuration greatly facilitates the synthesis, and a number of ligands have been prepared by varying the nitrogen and phosphorus substituents on the aminophosphine. These readily prepared phosphinoferrocenylaminophosphines, known as BoPhoz ligands, show surprising hydrolytic and air stability, with no degradation after 3 years open to the air. The rhodium complexes of these ligands show exceedingly high enantioselectivities (generally >95% ee) and activities often in excess of 50,000 catalyst turnovers per hour for the asymmetric hydrogenation of a wide variety of dehydro-alpha-amino acid and itaconic acid derivatives. They also show high activity and good to excellent enantioselectivity for the hydrogenation of a number of alpha-ketoesters. 相似文献
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We report herein the synthesis of cytotoxic cyanobactin, Wewakazole B through an efficient solution-phase approach. The key steps of the synthesis are the macrocyclic lactamization of linear dodecapeptide and construction of two hexapeptides with three different substituted oxazole rings. 相似文献
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D.M. Binnie J. Carr N.C. Debenham W.G. Jones H. Karami J. Keyne N.H. Sarma 《Physics letters. [Part B]》1979,83(1):141-146
In a high-resolution missing mass experiment the total width of the η′ (958) meson has been measured to be 0.28 ± 0.10 MeV. Using the known γγ branching ratio the value Γ(η′ → γγ) = 5.4 ± 2.1 keV is deduced. This is in good agreement with calculations based on fractional charge quarks and a pseudo-scalar mixing angle of 11°. 相似文献