422 research outputs found
<Abstract of Published Report>A Novel Approach for the Synthesis of Purine Acyclonucleosides Using 9-D-Ribitylpurines as a Chiral Pool.
<Abstract of Published Report>Ribofuranose-ring Cleavage of Purine Nucleosides with Diisobutylaliminum Hydride : Convenient Method for the Preparation of Purine Acyclonucleosides.
<Abstract of published report>Synthesis of a Ring-Scission Analogue of Neplanocin A as a Potential Inhibitor of S-Adenosylhomocysteine Hydrolase.
<Abstract of Published Report>Novel Synthesis of Purine Acyclonucleosides Possessing a Chiral 9-Hydroxyalkyl Group by Sugar Modification of 9-D-Ribitylpurines.
<Abstract of Published Report>A Convenient Synthesis of Acyclic Adenosines with an Unsaturated Side Chain by Modification of 9-(2,3-O-Isopropylidene-D-ribityl)adenine.
Defective graphene as a metal-free catalyst for chemoselective olefin hydrogenation by hydrazine
[EN] A series of defective graphenes containing or not containing N, B, S and other heteroatoms exhibited general activity as metal-free catalysts for the hydrogenation of C=C double bonds by hydrazine in the presence of oxygen. The best-performing graphene was the one obtained from the pyrolysis of alginate and subsequent exfoliation by sonication. The material was reusable in three consecutive runs without decay in its catalytic activity, and it exhibited 99% chemoselectivity for C=C double bonds vs. nitro group hydrogenation in contrast with conventional Pd supported on carbon, which was almost unselective. Theoretical calculations using a model for defective graphene for styrene hydrogenation showed adsorption of the substrate by - stacking, resulting in activation of the double bond and direct interaction of cis-diimide with the C=C group.AD thanks the University Grants Commission, New Delhi, for the award of an Assistant Professorship under its Faculty Recharge Program. AD also thanks the Department of Science and Technology, India, for the financial support through Extra Mural Research Funding (EMR/2016/006500). Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa SEV2016-0683, Grapas and CTQ2015-69563-CO2-1) and Generalitat Valenciana (Prometeo2017-083) is gratefully acknowledged.Dhakshinamoorthy, A.; He, J.; Franconetti, A.; Asiri, AM.; Primo Arnau, AM.; García Gómez, H. (2018). Defective graphene as a metal-free catalyst for chemoselective olefin hydrogenation by hydrazine. Catalysis Science & Technology. 8(6):1589-1598. https://doi.org/10.1039/c7cy02404eS1589159886J. G. de Vries and C. J.Elsevier , Handbook of homogeneous hydrogenations , Wiley-VCH , New York , 2007Monfette, S., Turner, Z. R., Semproni, S. P., & Chirik, P. J. (2012). Enantiopure C1-Symmetric Bis(imino)pyridine Cobalt Complexes for Asymmetric Alkene Hydrogenation. 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An Improved Synthesis of BrettPhos- and RockPhos-Type Biarylphosphine Ligands
Improved processes for the preparation of biphenyl-based phosphine ligands t-BuBrettPhos, RockPhos, and BrettPhos are presented. The new methods, featuring the use of Grignard reagents and catalytic amounts of copper, are superior to the previous methods, which require the use of tert-butyllithium and stoichiometric amounts of copper. Specifically, the use of less dangerous reagents provides a safer process, while the use of catalytic amounts of copper allows for the isolation of pure products in high yield. These improvements are particularly significant for the large-scale preparation of these ligands.National Institutes of Health (U.S.) (GM46059)Astellas USA Foundatio
Copper-Mediated Amidation of Heterocyclic and Aromatic C−H Bonds
A copper-mediated aerobic coupling reaction enables direct amidation of heterocycles or aromatics having weakly acidic C−H bonds with a variety of nitrogen nucleophiles. These reactions provide efficient access to many biologically important skeletons, including ones with the potential to serve as inhibitors of HMTs.Chemistry and Chemical Biolog
パラジウム炭素を触媒とした檜山クロスカップリング反応
檜山クロスカップリング反応は、フッ化物塩や塩基により活性化された有機ケイ素化合物と有機ハライド、あるいは有機ハライド等価体とのパラジウム(Pd)を触媒とした交差縮合反応である。本反応の基質である有機ケイ素化合物は毒性が低く、またグリニャール試薬などの求核剤と異なり空気中安定で取り扱いやすい。また、反応後に副生するケイ素化合物は、燃焼により無害な二酸化ケイ素に変換・処理されるため、檜山カップリングは医薬品を始めとした機能性物質の量産化反応に適している。従来法では均一系Pd 触媒を使用し、ゼロ価Pd の安定・活性化のためにリガンドが添加されるが、生成物中への残存や混入は避けることができず除去工程が別途必要となる。一方、不均一系Pd 触媒はPd が担体に保持されており化学的に安定であることから、均一系Pd 触媒を使用した際に生じる処理工程の回避が期待される。我々は接触水素化反応における汎用不均一系触媒であるパラジウム炭素(Pd/C)に着目し「Pd/C による檜山クロスカップリング反応」の開発並びにPd/C を触媒とした「リガンドを全く使用しない檜山クロスカップリング反応」の開発に成功した。特に後者はリガンドの添加を全く必要とせず、汎用されているPd/C を極微量使用するだけで効率良く進行する点で、操作性とコストに優れておりプロセス化学的適用が期待される。The Hiyama cross-coupling reaction, a palladium-catalyzed carbon–carbon bond formation between organosilanes andorganohalides or their equivalents, has been popularized as a useful synthetic method to construct unsymmetrical biphenyls asstructural components of various functional materials. The use of organosilanes as organometallic compounds, which was initiallyexplored by Hiyama, is one of the most attractive approaches, since organosilanes are easy to handle and environmentally friendlydue to their air-stability and low toxicity. Hiyama coupling has generally been achieved by the combined use of a homogeneouspalladium catalyst and a phosphine ligand. Recently, the development of heterogeneously palladium-catalyzed cross-couplingreactions has attracted significant attention from both environmental and economical points of view, since the catalysts can be readilyrecovered from the reaction mixture. Efficient methods are demonstrated for the palladium on carbon (Pd/C)-catalyzed Hiyamacross-coupling reactions and the first ligand-free Pd/C-catalyzed Hiyama cross-coupling reaction between a variety of aryl halidesand aryltriethoxysilanes
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