- Surface oxygen-assisted Pd nanoparticle catalysis for selective oxidation of silanes to silanols
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Just add O2: Based on the fact that an oxygen-adsorbed Pd metal surface shows higher reactivity for water dissociation than a clean Pd surface, carbon-supported Pd nanoparticles (NPs) with surface oxygen atoms were developed as a highly effective and reusable heterogeneous catalyst for selective oxidation of silanes to silanols with water as a green oxidant (see figure). Copyright
- Shimizu, Ken-Ichi,Kubo, Takahiro,Satsuma, Atsushi
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- Highly Functionalized Tricyclic Oxazinanones via Pairwise Oxidative Dearomatization and N-Hydroxycarbamate Dehydrogenation: Molecular Diversity Inspired by Tetrodotoxin
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Benzenoids in principle represent attractive and abundant starting materials for the preparation of substituted cyclohexanes; however, the synthetic tools available for overcoming the considerable aromatic energies inherent to these building blocks limit the available product types. In this paper, we demonstrate access to heretofore unknown heterotricyclic structures by leveraging oxidative dearomatization of 2-hydroxymethyl phenols with concurrent N-hydroxycarbamate dehydrogenation using a common oxidant. The pairwise-generated, mutually reactive species then participate in a second stage acylnitroso Diels-Alder cycloaddition. The reaction chemistry of the derived [2.2.2]-oxazabicycles, bearing four orthogonal functional groups and three stereogenic centers, is shown to yield considerable diversity in downstream products. The methodology allows for the expeditious synthesis of a functionalized intermediate bearing structural and stereochemical features in common with the complex alkaloid tetrodotoxin.
- Good, Steffen N.,Sharpe, Robert J.,Johnson, Jeffrey S.
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- ?-? Interactions and Bandwidths in "Molecular Metals". A Chemical, Structural, Photoelectron Spectroscopic, and Hartree-Fock-Slater Study of Monomeric and Cofacially Joined Dimeric Silicon Phthalocyanines
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This contribution describes an integrated chemical, physical, and quantum chemical approach to understanding ?-? interactions and tight-binding bandwidths in low-dimensional metallomacrocyclic "metals" via the properties of monomeric and dimeric stack fragments.Thus, electronic structure in the cofacially arrayed phtalocyaninato (Pc) polymer n has been explored through the complexes Si(Pc)(OR)2 and ROSi(Pc)OSi(Pc)OR (R=Si(CH3)2).Improved synthetic and purification procedures are described.Vibrational spectroscopy is employed to assign ROSi and Si(Pc)OSi(Pc) modes, and the results are correlated with data on n.The cofacial dimer crystallizes from chloroform in the orthorhombic space group Pbcn (No. 60) with four molecules in a unit cell of dimensions a=21.670(8), b=13.724(5), and c=23.031(9) Angstroem.Least-squares refinement led to a value for the conventional R index (on F) of 0.127 for 1975 independent reflections having 5 degMoKα0>/=3?(F0).The molecular structure consists of a cofacial (Pc)Si-O-Si(Pc) core of C2 symmetry, having virtually planar phtalocyanine rings, an Si-Si distance (interplanar spacing) of 3.32(1) Angstroem, Si-O-Si=179(1) deg, and a ring-ring staggering angle of 36.6 deg.The Si(CH3)2 capping groups are disordered.Electronic structure in the (phthalocyaninato)silicon monomer and dimer has been studied with first principles discrete variational local exchange (DV-Xα) techniques.These results are combined with transition-state calculations to interpret optical and high resolution He I and He II photoelectron spectroscopic data.While the conventional porphyrinic "four-orbital" model is supported for the low-energy optical transitions (excellent agreement between observed and calculated energies is noted), possible disagreements are noted at higher energies.Calculated (6.8 eV) and observed (6.46 eV) Si(Pc)(OR)2 ionization potentials are in good agreement.The lowest energy PES feature in the dimer is split by 0.29(3) eV.The splitting can be assigned to the cofacial HOMO-HOMO interaction and translates to a tight-binding bandwidth in the polymer of 0.58(6) eV.This result is in favorable agreement with a DV-Xα derived bandwidth of 0.76 eV and a value of 0.60 (6)eV previously obtained from a Drude analysis on I1.12>n.These results argue that the principal charge-transport pathway in the n polymer is via the Pc ? systems and that polaronic band-narrowing effects are minimal.
- Ciliberto, E.,Doris, K. A.,Pietro, W. J.,Reisner, G. M.,Ellis, D. E.,et al.
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- Catalysis by cationic oxorhenium(v): Hydrolysis and alcoholysis of organic silanes
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The cationic [2-(2′-hydroxyphenyl)-2-oxazolinato(-2)]oxorhenium(v) complex 1 promotes oxidative dehydrogenation of organosilanes with water and alcohols in a catalytic manner to give excellent yields of silanols and silyl ethers, respectively. The reactions proceed conveniently under ambient and open-flask conditions with low catalyst loading (≤1 mol%). The scope of the reaction with water is quite broad and includes aliphatic, aromatic, tertiary, secondary and primary silanes. The rate of reaction depends on the catalyst and silane concentrations and kinetic isotope effect measurements demonstrate involvement of the Si-H bond in the activated complex. The most influential factor on the silane affecting reactivity is steric hindrance and a quantitative correlation with the Taft steric parameter (E) is presented. A combination of kinetic data and isotope labelling results are used to discuss plausible mechanisms for the oxidative dehydrogenation reaction pathway.
- Corbin, Rex A.,Ison, Elon A.,Abu-Omar, Mahdi M.
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- Hydrogenation and Hydrosilylation of Nitrous Oxide Homogeneously Catalyzed by a Metal Complex
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Due to its significant contribution to stratospheric ozone depletion and its potent greenhouse effect, nitrous oxide has stimulated much research interest regarding its reactivity modes and its transformations, which can lead to its abatement. We report the homogeneously catalyzed reaction of nitrous oxide (N2O) with H2. The reaction is catalyzed by a PNP pincer ruthenium complex, generating efficiently only dinitrogen and water, under mild conditions, thus providing a green, mild methodology for removal of nitrous oxide. The reaction proceeds through a sequence of dihydrogen activation, "O"-atom transfer, and dehydration, in which metal-ligand cooperation plays a central role. This approach was further developed to catalytic O-transfer from N2O to Si-H bonds.
- Zeng, Rong,Feller, Moran,Ben-David, Yehoshoa,Milstein, David
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- Gold nanoparticles supported on the periodic mesoporous organosilica SBA-15 as an efficient and reusable catalyst for selective oxidation of silanes to silanols
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Gold nanoparticles are confined and stabilized within the channels of SBA-15 through the poly(ionic liquid) brushes that are anchored onto the pore walls of SBA-15. The supported gold catalyst exhibited remarkably high catalytic activities for selective oxidation of silanes into silanols using water as an oxidant without the use of organic solvents.
- Ma, Lina,Leng, Wenguang,Zhao, Yaopeng,Gao, Yanan,Duan, Hongdong
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- The selective catalytic oxidation of silanes to silanols with H2O2 activated by the Ti-beta zeolite
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Ti-beta catalyses the oxidation of small- and medium-sized silanes to the corresponding silanols by aqueous (30%) H2O2 as oxygen donor with high conversions and excellent selectivity (no disiloxane).
- Adam, Waldemar,Garcia, Hermenegildo,Mitchell, Catherine M.,Saha-Moeller, Chantu R.,Weichold, Oliver
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- Lewis acid-promoted reactions of γ-lactols with silyl enol ethers - Stereoselective formation of functionalized tetrahydrofuran derivatives
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The monosubstituted γ-lactols 1a, 1b, 1c, and 1d and the disubstituted γ-lactol 1e were converted into tetrahydrofuran derivatives by reaction with typical silyl enol ethers in the presence of Lewis acids. Although the most suitable Lewis acid appears to be zinc chloride, BF3·Et2O or diethylaluminium chloride are also suitable under appropriate conditions. The stereoselectivities of these substitution reactions are similar to those observed with other silylated nucleophiles; however, there are several important differences. A comparison of the diastereoselectivities of different γ-lactols and of various silylated nucleophiles and organometallic compounds will also be presented in this paper.
- Schmitt, Andreas,Reissig, Hans-Ulrich
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- Oxidation of Triorganosilanes and Related Compounds by Chlorine Dioxide
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Abstract: Oxidation of triethylsilane, tert-butyldimethylsilane, dimethylphenylsilane, triphenylsilane, 1,1,1,2tetramethyl-2-phenyldisilane, tris(trimethylsilyl)silane, hexamethyldisilane, tetrakis(trimethylsilyl)silane, 1,1,3,3tetraisopropyldisiloxane with chlorine dioxide was carried out. The reaction products of studied triorganosilanes with chlorine dioxide in an acetonitrile solution were the corresponding silanols and siloxanes. A mechanism explaining the formation of products and the observed regularities of the oxidation of silanes with chlorine dioxide has been proposed. A thermochemical analysis of some possible pathways in the gas phase using methods G4, G3, M05, and in an acetonitrile solution by the SMD-M05 method was carried out. The oxidation process can occur both with the participation of ionic and radical intermediates, depending on the structure of the oxidized substrate and medium.
- Grabovskiy, S. A.,Kabal’nova, N. N.
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p. 2391 - 2402
(2022/01/22)
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- Highly Selective Hydroxylation and Alkoxylation of Silanes: One-Pot Silane Oxidation and Reduction of Aldehydes/Ketones
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An efficient chemoselective iridium-catalyzed method for the hydroxylation and alkoxylation of organosilanes to generate hydrogen gas and silanols or silyl ethers was developed. A variety of sterically hindered silanes with alkyl, aryl, and ether groups were tolerated. Furthermore, this atom-economical catalytic protocol can be used for the synthesis of silanediols and silanetriols. A one-pot silane oxidation and chemoselective reduction of aldehydes/ketones was also realized.
- Luo, Nianhua,Liao, Jianhua,Ouyang, Lu,Wen, Huiling,Zhong, Yuhong,Liu, Jitian,Tang, Weiping,Luo, Renshi
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p. 165 - 171
(2020/01/21)
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- Selective Manganese-Catalyzed Oxidation of Hydrosilanes to Silanols under Neutral Reaction Conditions
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The first manganese-catalyzed oxidation of organosilanes to silanols with H2O2 under neutral reaction conditions has been accomplished. A variety of organosilanes with alkyl, aryl, alknyl, and heterocyclic substituents were tolerated, as well as sterically hindered organosilanes. The oxidation appears to proceed by a concerted process involving a manganese hydroperoxide species. Featuring mild reaction conditions, fast oxidation, and no waste byproducts, the protocol allows a low-cost, eco-benign synthesis of both silanols and silanediols.
- Wang, Kaikai,Zhou, Jimei,Jiang, Yuting,Zhang, Miaomiao,Wang, Chao,Xue, Dong,Tang, Weijun,Sun, Huamin,Xiao, Jianliang,Li, Chaoqun
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supporting information
p. 6380 - 6384
(2019/05/06)
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- Hafnium Triflate as a Highly Potent Catalyst for Regio- and Chemoselective Deprotection of Silyl Ethers
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As a Group IVB transition metal Lewis acid, hafnium triflate [Hf(OTf) 4 ] exhibited exceptionally high potency in desilylations. Since the amounts of Hf(OTf) 4 required for the deprotection of 1°, 2°, 3° alkyl and aryl tert -butyldimethylsilyl (TBS) ethers are significantly different, ranging from 0.05 mol% to 3 mol%, regioselective deprotection of TBS could be easily implemented. Moreover, chemoselective cleavage of different silyl ethers or removal of TBS in the presence of most hydroxyl protecting groups was also accomplished. NMR analyses of silyl products from TBS deprotection indicated that Hf(OTf) 4 -catalyzed desilylation may proceed via different mechanisms, depending on the solvent used.
- Zheng, Xiu-An,Kong, Rui,Huang, Hua-Shan,Wei, Jing-Ying,Chen, Ji-Zong,Gong, Shan-Shan,Sun, Qi
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p. 944 - 953
(2019/02/10)
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- Organosilane oxidation with a half million turnover number using fibrous nanosilica supported ultrasmall nanoparticles and pseudo-single atoms of gold
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The combination of ultrasmall nanoparticles and pseudo-single atoms of gold (Au) and fibrous nanosilica (KCC-1) functionalized with 3-aminopropyltriethoxysilane (APTS) enabled the design of KCC-1-APTS/Au nanocatalysts with very high turnover numbers (TONs). KCC-1-APTS/Au catalysed the oxidation of organosilanes to silanols, with a TON of approximately half a million (591000 for dimethylphenyl silane as a model substrate). Additionally, the figure-of-merit (FOM), which provides an integrated view of the rate of the reaction, the energy required, the reaction scale and the recyclability of the catalysts, was 633 mmol h-1 K-1. KCC-1-APTS/Au also catalysed two additional challenging reactions, the alcoholysis of silane and the hydrosilylation of aldehydes, with very high TONs. These characteristics make KCC-1-APTS/Au a versatile nanocatalyst.
- Dhiman, Mahak,Chalke, Bhagyashree,Polshettiwar, Vivek
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supporting information
p. 1935 - 1940
(2017/02/10)
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- Method for synthesizing silanol from silane through catalytic oxidation by bipyridine manganese catalyst
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The invention discloses a method for synthesizing silanol from silane through catalytic oxidation by a bipyridine manganese catalyst. The method employs a bipyridine manganese complex formed by coordination of a manganese salt and a dipyridine compound as a catalyst and clean environment-friendly hydrogen peroxide as an oxidizing agent for catalytic oxidation of silane into silanol. Compared with conventional methods, the method provided by the invention has the advantages that the catalyst is low in price; the preparation method is simple; raw materials are easily available; and the method is low in the usage amount of the catalyst, wide in the range of usable substrates, mild in reaction conditions, simple to operate, friendly to environment, short in reaction time, high in yield, good in selectivity, low in industrialization cost, etc.
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Paragraph 0014; 0015; 0016; 0017-0043; 0077; 0078; 0079
(2018/01/11)
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- Recombinant silicateins as model biocatalysts in organosiloxane chemistry
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The family of silicatein enzymes from marine sponges (phylum Porifera) is unique in nature for catalyzing the formation of inorganic silica structures, which the organisms incorporate into their skeleton. However, the synthesis of organosiloxanes catalyzed by these enzymes has thus far remained largely unexplored. To investigate the reactivity of these enzymes in relation to this important class of compounds, their catalysis of Si-O bond hydrolysis and condensation was investigated with a range of model organosilanols and silyl ethers. The enzymes' kinetic parameters were obtained by a high-throughput colorimetric assay based on the hydrolysis of 4-nitrophenyl silyl ethers. These assays showed unambiguous catalysis with kcat/Km values on the order of 2-50 min-1 μM-1. Condensation reactions were also demonstrated by the generation of silyl ethers from their corresponding silanols and alcohols. Notably, when presented with a substrate bearing both aliphatic and aromatic hydroxy groups the enzyme preferentially silylates the latter group, in clear contrast to nonenzymatic silylations. Furthermore, the silicateins are able to catalyze transetherifications, where the silyl group from one silyl ether may be transferred to a recipient alcohol. Despite close sequence homology to the protease cathepsin L, the silicateins seem to exhibit no significant protease or esterase activity when tested against analogous substrates. Overall, these results suggest the silicateins are promising candidates for future elaboration into efficient and selective biocatalysts for organosiloxane chemistry.
- Dakhili, S. Yasin Tabatabaei,Caslin, Stephanie A.,Faponle, Abayomi S.,Quayle, Peter,De Visser, Sam P.,Wong, Lu Shin
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p. E5285 - E5291
(2017/07/10)
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- Directing the crystallization of dehydro[24]annulenes into supramolecular nanotubular scaffolds
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The self-assembly of a series of dehydro[24]annulene derivatives into columnar stacks has been examined for its latent ability to form -conjugated carbon-rich nanotubular structures through topochemical polymerizations. We have studied the parameters affe
- Suzuki, Mitsuharu,Kotyk, Juliet F. Khosrowabadi,Khan, Saeed I.,Rubin, Yves
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supporting information
p. 5939 - 5956
(2016/06/09)
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- O2-enhanced catalytic activity of gold nanoparticles in selective oxidation of hydrosilanes to silanols
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O2 acts as a nonconsumed activator for gold nanoparticles (AuNPs) in the oxidation of hydrosilanes to silanols with water under O2 atmosphere, providing an acceleration of more than 200 times relative to the reaction rate under Ar atmosphere. The AuNP catalyst under aerobic conditions exhibits high activity in the oxidation with high turnover numbers (1230000). Various hydrosilanes including less-reactive bulky ones can be converted to the corresponding silanols in excellent yields. Moreover, the present AuNP catalyst is reusable while maintaining the high performance.
- Urayama, Teppei,Mitsudome, Takato,Maeno, Zen,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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supporting information
p. 1062 - 1064
(2015/09/02)
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- NOVEL SELECTIVE ANDROGEN RECEPTOR MODULATORS
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The present invention relates to a compound of Formula 1, 2 or 3: wherein A is N or —CR0—, where R0 is hydrogen, C1-C6 linear or branched chain alkyl, etc., Z is —CRe—, or, —N—, where Re is hydrogen, C1-C6 linear or branched chain alkyl,etc.; R1 is hydrogen, C1-C6 linear or branched chain alkyl, etc.; R2 are independently hydrogen or C1-C6 linear or branched chain alkyl; R3 and R4 are independently hydrogen, C1-C6 linear or branched chain alkyl, etc.;. R5 and R6 are independently hydrogen or C1-C6 linear or branched chain alkyl, etc.; R8 is hydrogen, C1-C6 linear or branched chain alkyl, etc.; R9 and R10 are independently hydrogen or C1-C6 linear or branched chain alkyl, etc.; Q is —CO—, —(CH2)q—, —(CHRs)q—, or (CRsRt)q—, where Rs and Rt are independently C1-C6 linear or branched chain alkyl, aryl, alkylaryl, heteroaryl or alkylheteroaryl; where q is 0, 1, 2, or 3; and, where n is 0, 1, 2, 3, 4 or 5; or, a pharmaceutically acceptable salt thereof, to compositions containing such compounds; and to the uses of such compounds in the treatment of various diseases, particularly, those affected or mediated by the androgen receptor.
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(2014/06/23)
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- Organocatalytic oxidation of organosilanes to silanols
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The oxidation of organosilanes to silanols constitutes an attractive transformation for both industry and academia. Bypassing the need for stoichiometric oxidants or precious metal catalytic complexes, the first organocatalytic oxidation of silanes has been accomplished. Catalytic amounts of 2,2,2-trifluoroacetophenone, in combination with the green oxidant H 2O2, lead to excellent to quantitative yields in a short reaction time. A variety of alkyl, aryl, alkenyl, and alkynyl substituents can be tolerated, providing an easy, cheap, efficient, and practical solution to a highly desirable transformation.
- Limnios, Dimitris,Kokotos, Christoforos G.
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p. 2239 - 2243
(2013/10/22)
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- N-silyloxaziridines: Synthesis and use for electrophilic amination
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N-Silyloxaziridines were synthesized for the first time. Their tert-butyldiphenylsilyl (TBDPS) derivatives were stable reagents that were prepared on a multigram scale in three steps and in 44% overall yield from the corresponding benzylamines. They were mild electrophilic aminating reagents that reacted at room temperature with diversely substituted primary and secondary amines to produce N-monoalkyl or N,N-dialkyl benzaldehyde hydrazones in 44a-87% yield.
- Richy, Nicolas,Ghoraf, Mohammed,Vidal, Jo?lle
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p. 10972 - 10977
(2013/02/22)
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- Selection and development of a route for cholesterol absorption inhibitor AZD4121
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The development of a synthetic route to the cholesterol absorption inhibitor AZD4121 is presented. Key steps are a highly enantioselective CBS reduction, a stereospecific Staudinger reaction, an amine/lithium chloride mediated ester hydrolysis, and a resolution of a 50:50 diastereomeric mixture by recrystallization. The synthesis was accomplished in 10 linear steps, and the overall yield, when compared with the lead optimization (LO) route, was improved from 1% to 20%. All purifications of intermediates through preparative HPLC or silica gel chromatography were avoided. This was possible since many of the intermediates along the route could be used as such in the next step until an intermediate with suitable crystalline properties could be identified and purified through crystallization.
- Karlsson, Staffan,Soerensen, J. Henrik
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experimental part
p. 586 - 594
(2012/07/03)
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- Di- tert -butylisobutylsilyl, another useful protecting group
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The di-tert-butylisobutylsilyl (BIBS) protecting group offers new possibilities for synthetic processes because of its steric bulk, robustness of its derivatives, and other special properties.
- Liang, Huan,Hu, Lin,Corey
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scheme or table
p. 4120 - 4123
(2011/10/04)
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- Nonclassical ruthenium silyl dihydride complexes TpRu(PPh 3)(I?·3-HSiR3H) [Tp = hydridotris(pyrazolyl)borate]: Catalytic hydrolytic oxidation of organosilanes to silanols with TpRu(PPh3)(I?·3-HSiR 3H)
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An X-ray crystallographic study showed that it is more appropriate to describe the complexes TpRu(PPh3)"H2SiR 3" as TpRu(PPh3)(I?·3- HSiR3H), a static structure containing HA?·A? ·A?·SiA?·A?·A?·H bonding rather than a highly fluxional pair ofI?-silane hydride species TpRu(PPh3)(Ha)(I?·2-H bSiR3) [rlhar2] TpRu(PPh3)(H b)(I?·2-HaSiR3). One of the complexes was used for the catalytic hydrolytic oxidation of organosilanes to silanols. A mechanism, which does not involve the usual oxidative addition of silane to the metal center to form the silyl hydride species, is proposed, which is supported by theoretical calculations.
- Lee, Ting Yan,Dang, Li,Zhou, Zhongyuan,Yeung, Chi Hung,Lin, Zhenyang,Lau, Chak Po
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experimental part
p. 5675 - 5684
(2011/03/17)
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- Highly selective oxidation of organosilanes to silanols with hydrogen peroxide catalyzed by a lacunary polyoxotungstate
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Silanol synthesis: Divacant lacunary polyoxotungstate (nBu4N+)4[g- SiW10O34(H2O)2] (I) is an efficient homogeneous catalyst for highly selective oxidation of organosilanes to silanols with 30/60% aqueous H2O2. Various kinds of silanes 1 containing aryl, alkyl, alkenyl, alkynyl and alkoxy groups are chemoselectively converted into the corresponding silanols 2 in high yields with only one equivalent of aqueous H2O2 with respect to the substrate.
- Ishimoto, Ryo,Kamata, Keigo,Mizuno, Noritaka
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supporting information; experimental part
p. 8900 - 8904
(2010/01/16)
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- Supported gold nanoparticle catalyst for the selective oxidation of silanes to silanols in water
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Hydroxyapatite-supported gold nanoparticles (AuHAP) can act as highly efficient and reusable catalysts for the oxidation of diverse silanes into silanols in water; this is the first catalytic methodology for the selective synthesis of aliphatic silanols using water under organic-solvent-free conditions.
- Mitsudome, Takato,Noujima, Akifumi,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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supporting information; experimental part
p. 5302 - 5304
(2010/01/31)
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- Primary alkyl bromides from dimethylthiocarbamates
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The conversion of primary alkyl dimethylthiocarbamates into alkyl bromides using the Vilsmeier reagent occurs in high yields in the presence of other non-acid sensitive and non-nucleophilic functional groups. Georg Thieme Verlag Stuttgart · New York.
- Moynihan, Meghan F.,Tucker, Joseph W.,Abelt, Christopher J.
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experimental part
p. 3565 - 3568
(2009/06/18)
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- Kinase Inhibitors
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The present invention relates to organic molecules capable of modulating tyrosine kinase signal transduction in order to regulate, modulate and/or inhibit abnormal cell proliferation.
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Page/Page column 89
(2008/06/13)
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- SUBSTITUTED IMIDAZO RING SYSTEMS AND METHODS
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Imidazo ring systems substituted at the 1-position, pharmaceutical compositions containing the compounds, intermediates, methods of making the compounds, and methods of use of these compounds as immunomodulators, for inducing cytokine biosynthesis in anim
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Page/Page column 77
(2008/06/13)
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- Efficient heterogeneous oxidation of organosilanes to silanols catalysed by a hydroxyapatite-bound Ru complex in the presence of water and molecular oxygen
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RuHAP is a highly selective and reusable catalyst for the oxidation of a wide variety of organosilanes to the corresponding silanols in the presence of water and molecular oxygen.
- Mori, Kohsuke,Tano, Makoto,Mizugaki, Tomoo,Ebitani, Kohki,Kaneda, Kiyotomi
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p. 1536 - 1538
(2007/10/03)
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- Genenation of 1-azapentadienyl anion from N-(tert-butyldimethylsilyl)-3-buten-1-amine
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N-(tert-Butyldimethylsilyl)-3-buten-1-amine undergoes allylic deprotonation at the 2-position when exposed to 2 equiv of nBuLi in THF. This allylic anion undergoes lithium hydride elimination to generate a 1-azapentadienyl anion. The anion is generated cleanly and completely.
- Jacobson, Madeleine A.,Williard, Paul G.
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p. 3915 - 3918
(2007/10/03)
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- Indium metal as a reducing agent in organic synthesis
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The low first ionisation potential (5.8 eV) of indium coupled with its stability towards air and water, suggest that this metallic element should be a useful reducing agent for organic substrates. The use of indium metal for the reduction of C=N bonds in imines, the heterocyclic ring in benzo-fused nitrogen heterocycles, of oximes, nitro compounds and conjugated alkenes and the removal of 4-nitrobenzyl protecting groups is described. Thus the heterocyclic ring in quinolines, isoquinolines and quinoxalines is selectively reduced using indium metal in aqueous ethanolic ammonium chloride. Treatment of a range of aromatic nitro compounds under similar conditions results in selective reduction of the nitro groups; ester, nitrile, amide and halide substituents are unaffected. Likewise indium in aqueous ethanolic ammonium chloride is an effective method for the deprotection of 4-nitrobenzyl ethers and esters. Indium is also an effective reducing agent under non-aqueous conditions and α-oximino carbonyl compounds can be selectively reduced to the corresponding N-protected amine with indium powder, acetic acid in THF in the presence of acetic anhydride or di-tert-butyl dicarbonate. Conjugated alkenes are also reduced by indium in THF-acetic acid.
- Pitts,Harrison,Moody
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p. 955 - 977
(2007/10/03)
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- NaY zeolite as host for the selective heterogeneous oxidation of silanes and olefins with hydrogen peroxide catalyzed by methyltrioxorhenium
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The methyltrioxorhenium(MTO)-catalyzed oxidation of silanes to silanols and the epoxidation of various olefins by aqueous 85% H2O2 proceed in high yields and excellent product selectivities (no disiloxanes, diols) in the presence of the zeolite NaY. The oxidative species is located inside the 12- A supercages. This prevents the bimolecular condensation of the silanol to disiloxane by steric means and the Lewis-acid assisted hydrolysis of the epoxide to the diol.
- Adam, Waldemar,Saha-Moeller, Chantu R.,Weichold, Oliver
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p. 2897 - 2899
(2007/10/03)
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- Properties and Reactions of Substituted 1,2-Thiazetidine 1,1-Dioxides: Acylation of β-Sultams at C-4, Reduction of 4-Acyl-β-sultams, and Stereochemistry of 4-(α-Hydroxyalkyl)-β-sultams
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Acylation of N-silylated and 2,3-substituted 1,2-thiazetidine 1,1-dioxides (β-sultams) results in the formation of 4-acylated β-sultams 2 and 8.The desilylation of 2 to 3 is easily done with TBAF either on silica gel or in ethanolic solution.The acylated
- Mueller, Martin,Otto, Hans-Hartwig
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p. 171 - 178
(2007/10/02)
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- Synthesis of 3,4-Disubstituted 3,4-Dihydro-2-pyrones via 2-(Silyloxy)pyrylium Salts: Regioselective Introduction of Substituents into 2-Pyrones
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Silylation of 4,6-dimethyl- and 6-methyl-2-pyrone with tert-butyldimethylsilyl triflate affords the corresponding 2-(silyloxy)pyrylium triflates 2 quantitatively.Lithium diorganocuprates add regioselectively at position 4 of triflates 2 to give 4-substituted 2-(silyloxy)-4H-pyrans 4.Compounds 4 react with electrophiles at position 3 to give 3-bromo- (8), 3-(silyloxy)- (9), 3-methylene- (15), and 3-(1-hydroxybutyl)-3,4-dihydro-2-pyrones (16).
- Kume, Takashi,Kojima, Toshikatsu,Iwasaki, Hideharu,Yamamoto, Yohsuke,Akiba, Kin-ya
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p. 1931 - 1935
(2007/10/02)
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- Mechanism of Intramolecular Photocycloadditions of Cyclooctenones
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The intramolecular photochemical cycloadditions of a number of 4'-substituted (3'-butenyloxy)-cyclooctenones have been studied.Two classes of substrates were found.One class (phenyl- and vinyl-substituted) forms adducts in an efficient reaction, while the rest of the compounds from photoproducts slowly and in low yield.The behavior of a carbon analogue shows that rotational relaxation of the cyclooctenone triplet is faster than cycloaddition.Based on quenching and sensitization studies, it has been suggested that the substituent effect is indicative of an enhanced rate of cyclization to form a 1,4-biradical.
- Pirrung, Michael C.,Webster, Nicholas J. G.
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p. 3603 - 3613
(2007/10/02)
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- PH DEPENDENCE OF HYDROLYTIC REMOVAL OF SILYL GROUP FROM TRIALKYLSILYL ETHERS
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Rate constants for the acid and base-catalyzed hydrolysis of the trialkylsilyl ethers of alcohols were quantitatively correlated with Taft's ?* and Es values of the substituens on Si and O atoms of the ether linkage.The regression equations for kH and kOH were satisfactorily computed.
- Shirai, Naohiro,Moriya, Kiyoshi,Kawazoe, Yutaka
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p. 2211 - 2214
(2007/10/02)
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- Mechanistic Change in Acid-Catalyzed Hydrolysis of Silyl Vinyl Ethers
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tert-Butyldimethylsilyl vinyl ethers t-BuMe2SiOCR=CH2 hydrolyze in 50percent CH3CN - H2O with general and specific acid catalysis and a linear dependence of log kH+ on ?p+(R), indicating that the reaction occurs with rate-determing proton transfer to carbon (the ADE2 mechanism).By contrast the rates of trimethylsilyl vinyl ethers Me3SiOCR=CH2 are not correlated by ?p+(R) but still depend on proton and general acid concentrations.Nucleophilic attack on silicon is implicated in the rate-determing step of the latter compounds, and the possibilities for the details of this process are considered.
- Novice, Marilyn H.,Seikaly, Hani R.,Seiz, Annette D.,Tidwell, Thomas T.
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p. 5835 - 5838
(2007/10/02)
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