共查询到20条相似文献,搜索用时 15 毫秒
1.
An intramolecular σ-bond metathesis between carbon-carbon and silicon-silicon bonds took place on treatment of a disilane tethered to a cyclobutanone with a palladium(0) catalyst, furnishing a silaindane skeleton as well as an acylsilane functionality at once. 相似文献
2.
Yuanfu Tang Jing Xiang Linfeng Cun Yuqin Wang Jin Zhu Jian Liao Jingen Deng 《Tetrahedron: Asymmetry》2010,21(15):1900-1905
Asymmetric transfer hydrogenation of β,β-disubstituted nitroalkenes catalyzed by a chiral diamine–rhodium complex in combination with HCO2Na–HCO2H as a hydrogen source in water was successfully realized with high reactivity, excellent chemoselectivity and good enantioselectivity. The metal precursor and pH value of the aqueous solution have a large influence on the reactivity and chemoselectivity. The substituents on the benzene rings and the sulfonyl groups of TsDPEN have significant effects on the enantioselectivity. This catalytic asymmetric transformation is one of the most practical pathways to obtain optically active nitroalkanes. 相似文献
3.
Susan Lühr Jens Holz Odalys Zayas Oliver Seidelmann Lutz Domke Armin Börner 《Tetrahedron: Asymmetry》2013,24(7):395-401
The stereoselective synthesis of chiral β2-homoalanine derivatives with 99% ee by the Rh-catalyzed enantioselective hydrogenation of prochiral 2-aminomethyl acrylates is described. The subsequent transformation to chiral 3-amino-2-methylpropanols is also demonstrated. 相似文献
4.
Hui-Qi Ni Jing-Cheng Dai Dr. Shouliang Yang Dr. Richard P. Loach Matthew D. Chuba Dr. Indrawan J. McAlpine Prof. Keary M. Engle 《Angewandte Chemie (International ed. in English)》2023,62(34):e202306581
We describe a catalytic cascade sequence involving directed C(sp3)−H activation followed by β-heteroatom elimination to generate a PdII(π-alkene) intermediate that then undergoes redox-neutral annulation with an ambiphilic aryl halide to access 5- and 6-membered (hetero)cycles. Various alkyl C(sp3)−oxygen, nitrogen, and sulfur bonds can be selectively activated, and the annulation proceeds with high diastereoselectivity. The method enables modification of amino acids with good retention of enantiomeric excess, as well as σ-bond ring-opening/ring-closing transfiguration of low-strain heterocycles. Despite its mechanistic complexity, the method employs simple conditions and is operationally straightforward to perform. 相似文献
5.
《Journal of Molecular Catalysis #》1981,10(3):305-311
α-Acylaminocinnamic acids and esters are hydrogenated with rhodium (I) complex containing (2R, 4R)-cis-bis(diphenylphosphinomethyl)-1,3-dioxolan. The Z acids give enantiomeric excess up to 79% in the presence of triethylamine; increasing the steric bulk of the enamide moiety has only a small effect on the enantiomeric excess. The esters are reduced with low optical yield. 相似文献
6.
《Tetrahedron: Asymmetry》1998,9(16):2773-2775
The asymmetric hydrogenation of (E)-α,β-bis(N-acylamino)acrylates was promoted by a rhodium complex bearing a trans-chelating chiral diphosphine ligand (R,R)-(S,S)-PrTRAP, providing the corresponding optically active (2S,3R)-2,3-bis(N-acylamino)carboxylates with 79–82% ee. The 2,3-bis(N-acylamino)carboxylates isolated were readily hydrolyzed under acid to afford (2S,3R)-2,3-diaminocarboxylic acids in 95% yield without epimerization. 相似文献
7.
Shoji Y Matsuo T Hashizume D Gutmann MJ Fueno H Tanaka K Tamao K 《Journal of the American Chemical Society》2011,133(29):11058-11061
Diborane(6) as a H-bridged dimer of monoborane can be converted cleanly by two-electron reduction into diborane(6) dianion, which is isoelectronic with ethane, through B-B σ-bond formation when each boron atom has a bulky ligand on it. The existence of the B-B σ bond is supported by the X-ray molecular structure [B-B bond length of 1.924(3) ?], NMR studies, magnetic susceptibility measurements, and DFT calculations. Stepwise hydride abstraction reactions of the diborane(6) dianion produce the corresponding H-bridged diborane(5) anion and doubly H-bridged diborane(4) without B-B bond scission. 相似文献
8.
《Tetrahedron: Asymmetry》2001,12(16):2337-2342
The chiral ligands H8–BINAPO and H8–BDPAB were synthesized by reacting chlorodiphenylphosphine with H8–BINOL and H8–BINAM, respectively. Applications of these ligands in the Rh-catalyzed enantioselective hydrogenation of a variety of (Z)-acetamido-3-arylacrylic acid methyl esters provided chiral amino acid derivatives with good to excellent enantioselectivities (H8–BINAPO: up to 84.0% e.e.; H8–BDPAB: up to 97.1% e.e.). In the hydrogenation of acetamidoacrylic acid, 99% e.e. was obtained when a [Rh(H8–BDPAB)]+ catalyst was used. The catalytic activities and enantioselectivities of [Rh(H8–BINAPO)]+ and [Rh(H8–BDPAB)]+ are substantially better than those obtained with the corresponding rhodium catalysts containing BINAPO (up to 64% e.e.) and BDPAB (up to 92.6% e.e.). 相似文献
9.
A new rhodium-based catalytic system for the direct C-H coupling of arenes and iodoarenes that shows high activity with reasonably broad scope was developed. Under the catalytic influence of RhCl(CO){P[OCH(CF3)2]3}2 and Ag2CO3, the direct C-H arylation of heteroarenes and arenes took place with iodoarenes to afford a range of biaryls in good to excellent yields with high regioselectivity. Thiophenes, furans, pyrroles, indoles, and alkoxybenzenes are applicable to this arylation protocol. 相似文献
10.
The phosphonate analogue of α-N-benzoyl protected phenylalanine methylester has been prepared by catalytic synthesis. Commonly used Rh-complexes has been applied in asymmetric hydrogenation to check their usefulness in the standard reaction. 相似文献
11.
Andrey I. Poddel’sky Vladimir K. Cherkasov Michail P. Bubnov Ludmila G. Abakumova Gleb A. Abakumov 《Journal of organometallic chemistry》2005,690(1):145-150
New square-planar (Ph3P)NiII(o-Tol)(ISQ-Pri) (1), (Ph3P)NiII(o-Tol)(ISQ-Me) (2), (Ph3P)NiII(o-Tol)(ISQ-But) (3) nickel complexes (where ISQ-Pri = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate, ISQ-Me = 4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate, ISQ-But = 4,6-di-tert-butyl-N-(2,5-di-tert-butylphenyl)-o-iminobenzosemiquinonate, o-Tol = o-tolyl ligand) have been synthesized. Complexes contain σ-bound o-tolyl and neutral donor ligand Ph3P. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands lead to the tetrahedral distortion of square-planar configurations of complexes as it was established using EPR spectroscopy. 相似文献
12.
《Tetrahedron: Asymmetry》1999,10(10):1887-1893
The construction of a chiral catalyst system embedded at a specific site in a protein has been studied. The preparation of the biotinylated Pyrphos–Rh(I) complex attached to the binding site in avidin and its application to the asymmetric hydrogenation of itaconic acid have been investigated. By introducing the chiral Pyrphos–Rh(I) moiety into the constrained environment of the protein cavity it was found that the enantioselectivity of the system was significantly influenced by the tertiary conformation within the avidin cavity. The effects of reaction conditions such as temperature, hydrogen pressure, and the pH value of the buffer on enantioselectivity are reported. 相似文献
13.
《Comptes Rendus Chimie》2002,5(4):303-308
A novel tridentate hemilabile ligand 2 containing phosphine, imine and pyridyl donor groups has been prepared in analogy with the synthesis of the known related ligand 1. The reaction of 1 or 2 with 〚Rh(COE)2Cl〛2 resulted in the formation of the neutral complexes 〚Rh(L)Cl〛. By a method using 〚M(diene)Cl〛2 as starting material, cationic complexes of the type 〚M(diene)(L)〛X were also obtained (M = Rh, diene = NBD, L = 1, 2; M = Ir, diene = COD, L = 1; X = BF4, OTf). A comparative study of the catalytic activity of the new complexes towards the hydrogenation of various olefins has been reported. In particular, the catalysts of the type 〚Rh(L)Cl〛 are remarkably active when prepared in situ, especially for the reduction of hindered olefins. 相似文献
14.
Takahiro Soeta Yuuki KojimaYutaka Ukaji Katsuhiko Inomata 《Tetrahedron letters》2011,52(20):2557-2559
A first example of diphenylborinic acid catalyzed α-addition to isocyanide with aldehyde and water is described. The reaction proceeded smoothly in the presence of water and 5 mol % of borinic acid to give the corresponding α-hydroxyamides in good to high yields. A wide range of aldehydes and isocyanides are applicable to this reaction. 相似文献
15.
An intriguing and operationally simple direct benzylation of hydroquinones with benzhydryl alcohols has been developed using PTSA in water, affording functionalized hydroquinones in good to excellent yields. The advantages of being environmentally benign, metal-free, base-free, easy workup and having a wide substrate scope make it a promising process for the synthesis of symmetrically and unsymmetrically benzylated hydroquinones as well as for industrial applications. 相似文献
16.
Shirakawa S Liu K Ito H Maruoka K 《Chemical communications (Cambridge, England)》2011,47(5):1515-1517
Efficient catalytic asymmetric synthesis of 1,1-disubstituted tetrahydro-β-carbolines has been achieved via asymmetric alkylation of 1-cyanotetrahydro-β-carbolines using a binaphthyl-modified N-spiro-type chiral phase-transfer catalyst. This is a valuable example of hitherto difficult highly enantioselective alkylations at α-carbon of the cyano group under phase-transfer conditions. 相似文献
17.
An efficient decarboxylative alkylation reaction of β-keto acids with N-benzylic or N-allylic sulfonamides has been developed, for the first time, through sequential cleavage of carbon-nitrogen and carbon-carbon bonds in the presence of 10 mol% of FeCl(3). 相似文献
18.
Megharaja Holiyachi Samundeeswari L. Shastri Bahubali M. Chougala Vinay A. Sunagar 《合成通讯》2016,46(16):1386-1395
Organocatalyzed direct intermolecular aldol reactions have been developed for substituted 4-formylcoumarins with acetone in water using L-proline and phthalimido-prolinamide catalysts without use of additives. Stereoselective products obtained were in excellent yields (up to 97%) with high purity (up to 99%) and enatioselectivities (up to 95%). The isolated compounds were confirmed by infrared, NMR, high-performance liquid chromatography, and mass spectrometry and some of them by single-crystal x-ray crystallography. 相似文献
19.
《Tetrahedron: Asymmetry》1998,9(23):4193-4202
Several kinds of micelle forming amphiphiles were tested in the asymmetric hydrogenation of the prochiral dialkyl 1-benzamido-2-phenyl-ethenephosphonates in aqueous media. The chiral catalytic system [Rh(cod)2]BF4/BPPM or amphiphilized PPM proved to be suitable for the hydrogenation reaction affording enantiomeric excesses up to 99%. A chiral induction is possible to a certain extent (up to 11% ee) by selected chiral amphiphiles in the presence of achiral rhodium catalysts. 相似文献
20.
Trimerization of 2-methylpropanal (isobutyraldehyde) is a simple and effective method to synthesize 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol-3-monoisobutyrate which are often used as film forming auxiliaries in paints. The use of solid sodium hydroxide as a catalyst provides an excellent yield of above 85 % after the optimization of the reaction time and the catalyst dosage. Furthermore, trimerization of four other aldehydes with one α-hydrogen catalyzed by solid sodium hydroxide can also take place and the yield of 1,3-diol monoesters reaches 50–70 %. Trimerization of aldehydes with one α-hydrogen can be explained by a three-step reaction mechanism: (i) aldol condensation of aldehyde; (ii) crossed Cannizzaro reaction; and (iii) esterification of carboxylic acid and alcohol. 相似文献