- Tropylium-Promoted Hydroboration Reactions: Mechanistic Insights Via Experimental and Computational Studies
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Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross-coupling chemistry. This type of reaction has traditionally been mediated by transition-metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic pathway, which is triggered by the hydride abstraction of pinacolborane with tropylium ion. This is followed by a series ofin situcounterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction.
- Mai, Binh Khanh,Nguyen, Thanh Vinh,Ton, Nhan N. H.
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p. 9117 - 9133
(2021/07/19)
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- Borane evolution and its application to organic synthesis using the phase-vanishing method
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Although borane is a useful reagent, it is difficult to handle. In this study, borane was generated in situ from NaBH4 or nBu4NBH4 with several oxidants using a phase-vanishing (PV) method. The borane generated was directly reacted with alkenes, affording the desired alcohols in good yields after oxidation with H2O2 under basic conditions. The selective reduction of carboxylic acids with the evolved borane was examined. The organoboranes generated by the PV method successfully underwent Suzuki–Miyaura coupling. Using this PV system, reactions with borane can be carried out easily and safely in a common test tube.
- Soga, Nene,Yoshiki, Tomo,Sato, Aoi,Kawamoto, Takuji,Ryu, Ilhyong,Matsubara, Hiroshi
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supporting information
(2021/03/26)
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- Regiodivergent Hydroborative Ring Opening of Epoxides via Selective C-O Bond Activation
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A magnesium-catalyzed regiodivergent C-O bond cleavage protocol is presented. Readily available magnesium catalysts achieve the selective hydroboration of a wide range of epoxides and oxetanes yielding secondary and tertiary alcohols in excellent yields and regioselectivities. Experimental mechanistic investigations and DFT calculations provide insight into the unexpected regiodivergence and explain the different mechanisms of the C-O bond activation and product formation.
- Magre, Marc,Paffenholz, Eva,Maity, Bholanath,Cavallo, Luigi,Rueping, Magnus
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supporting information
p. 14286 - 14294
(2020/09/15)
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- Diaminodiphosphine tetradentate ligand and ruthenium complex thereof, and preparation methods and applications of ligand and complex
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The invention discloses a diaminodiphosphine tetradentate ligand and a ruthenium complex thereof, and preparation methods and applications of the ligand and the complex, and provides a ruthenium complex represented by a formula I, wherein L is a diaminodiphosphine tetradentate ligand represented by a formula II, and X and Y are respectively and independently chlorine ion, bromine ion, iodine ion,hydrogen negative ion or BH4. According to the present invention, the ruthenium complex exhibits excellent catalytic activity in the catalytic hydrogenation reactions of ester compounds, has high yield and high chemical selectivity, is compatible with conjugated and non-conjugated carbon-carbon double bond, carbon-carbon triple bond, epoxy, halogen, carbonyl and other functional groups, and hasgreat application prospects.
- -
-
Paragraph 0301-0303; 0305
(2019/11/04)
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- Ruthenium-Catalyzed Selective Hydrogenation of Epoxides to Secondary Alcohols
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A ruthenium(II)-catalyzed highly selective Markovnikov hydrogenation of terminal epoxides to secondary alcohols is reported. Diverse substitutions on the aryl ring of styrene oxides are tolerated. Benzylic, glycidyl, and aliphatic epoxides as well as diepoxides also underwent facile hydrogenation to provide secondary alcohols with exclusive selectivity. Metal-ligand cooperation-mediated ruthenium trans-dihydride formation and its reaction involving oxygen and the less substituted terminal carbon of the epoxide is envisaged for the origin of the observed selectivity.
- Thiyagarajan, Subramanian,Gunanathan, Chidambaram
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supporting information
p. 9774 - 9778
(2019/12/02)
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- Visible-Light-Mediated Aerobic Oxidation of Organoboron Compounds Using in Situ Generated Hydrogen Peroxide
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A simple and general visible-light-mediated oxidation of organoboron compounds has been developed with rose bengal as the photocatalyst, substoichiometric Et3N as the electron donor, as well as air as the oxidant. This mild and metal-free protocol shows a broad substrate scope and provides a wide range of aliphatic alcohols and phenols in moderate to excellent yields. Notably, the robustness of this method is demonstrated on the stereospecific aerobic oxidation of organoboron compounds.
- Weng, Wei-Zhi,Liang, Hao,Zhang, Bo
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p. 4979 - 4983
(2018/08/24)
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- Antiproliferative activity and SARs of caffeic acid esters with mono-substituted phenylethanols moiety
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A series of CAPE derivatives with mono-substituted phenylethanols moiety were synthesized and evaluated by MTT assay on growth of 4 human cancer cell lines (Hela, DU-145, MCF-7 and ECA-109). The substituent effects on the antiproliferative activity were systematically investigated for the first time. It was found that electron-donating and hydrophobic substituents at 2′-position of phenylethanol moiety could significantly enhance CAPE's antiproliferative activity. 2′-Propoxyl derivative, as a novel caffeic acid ester, exhibited exquisite potency (IC50?=?0.4?±?0.02 & 0.6?±?0.03?μM against Hela and DU-145 respectively).
- Xie, Jin,Yang, Fengzhi,Zhang, Man,Lam, Celine,Qiao, Yixue,Xiao, Jia,Zhang, Dongdong,Ge, Yuxuan,Fu, Lei,Xie, Dongsheng
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p. 131 - 134
(2016/12/27)
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- Regioselective hydrosilylation of epoxides catalysed by nickel(II) hydrido complexes
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Bench-stable nickel fluoride complexes bearing NNN pincer ligands have been employed as precursors for the regioselective hydrosilylation of epoxides at room temperature. A nickel hydride assisted epoxide opening is followed by the cleavage of the newly formed nickel oxygen bond by σ-bond metathesis with a silane.
- Wenz, Jan,Wadepohl, Hubert,Gade, Lutz H.
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p. 4308 - 4311
(2017/04/21)
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- Biocatalytic Formal Anti-Markovnikov Hydroamination and Hydration of Aryl Alkenes
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Biocatalytic anti-Markovnikov alkene hydroamination and hydration were achieved based on two concepts involving enzyme cascades: epoxidation-isomerization-amination for hydroamination and epoxidation-isomerization-reduction for hydration. An Escherichia coli strain coexpressing styrene monooxygenase (SMO), styrene oxide isomerase (SOI), ω-transaminase (CvTA), and alanine dehydrogenase (AlaDH) catalyzed the hydroamination of 12 aryl alkenes to give the corresponding valuable terminal amines in high conversion (many ≥86%) and exclusive anti-Markovnikov selectivity (>99:1). Another E. coli strain coexpressing SMO, SOI, and phenylacetaldehyde reductase (PAR) catalyzed the hydration of 12 aryl alkenes to the corresponding useful terminal alcohols in high conversion (many ≥80%) and very high anti-Markovnikov selectivity (>99:1). Importantly, SOI was discovered for stereoselective isomerization of a chiral epoxide to a chiral aldehyde, providing some insights on enzymatic epoxide rearrangement. Harnessing this stereoselective rearrangement, highly enantioselective anti-Markovnikov hydroamination and hydration were demonstrated to convert α-methylstyrene to the corresponding (S)-amine and (S)-alcohol in 84-81% conversion with 97-92% ee, respectively. The biocatalytic anti-Markovnikov hydroamination and hydration of alkenes, utilizing cheap and nontoxic chemicals (O2, NH3, and glucose) and cells, provide an environmentally friendly, highly selective, and high-yielding synthesis of terminal amines and alcohols.
- Wu, Shuke,Liu, Ji,Li, Zhi
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p. 5225 - 5233
(2017/08/17)
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- Anti-Markovnikov alkene oxidation by metal-oxo–mediated enzyme catalysis
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Catalytic anti-Markovnikov oxidation of alkene feedstocks could simplify synthetic routes to many important molecules and solve a long-standing challenge in chemistry. Here we report the engineering of a cytochrome P450 enzyme by directed evolution to catalyze metal-oxo–mediated anti-Markovnikov oxidation of styrenes with high efficiency. The enzyme uses dioxygen as the terminal oxidant and achieves selectivity for anti-Markovnikov oxidation over the kinetically favored alkene epoxidation by trapping high-energy intermediates and catalyzing an oxo transfer, including an enantioselective 1,2-hydride migration. The anti-Markovnikov oxygenase can be combined with other catalysts in synthetic metabolic pathways to access a variety of challenging anti-Markovnikov functionalization reactions.
- Hammer, Stephan C.,Kubik, Grzegorz,Watkins, Ella,Huang, Shan,Minges, Hannah,Arnold, Frances H.
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p. 215 - 218
(2017/10/19)
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- Cp2TiCl2-catalyzed cycloboration of α-olefins with PhBCl2in the synthesis of 2-alkyl(aryl,benzyl)-1-phenylboriranes
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A one-pot method for the synthesis of 2-alkyl(aryl, benzyl)-1-phenylboriranes has been developed via the reaction of α-olefins with PhBCl2in the presence of Cp2TiCl2as the catalyst. The method implies the formation of boriranes as the result of transmetalation of titanacyclopropane intermediates generated in the reaction of α-olefins with Cp2TiCl2. Individual 1-phenyl-2-substituted boriranes were isolated and their structures confirmed by NMR spectral methods.
- Khusainova, Liliya I.,Khafizova, Leila O.,Tyumkina, Tatyana V.,Ryazanov, Kirill S.,Dzhemilev, Usein M.
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- Synthesis of 5,6-Dihydropyrazolo[5,1-a]isoquinoline and Ethyl (Z)-3-Acetoxy-3-tosylpent-4-enoate through Tertiary-Amine-Catalyzed [3+2] Annulation
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The 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyzed divergent [3+2] annulation of C,N-cyclic azomethine imines with δ-acetoxyallenoates was developed; 5,6-dihydropyrazolo[5,1-a]isoquinolines and ethyl (Z)-3-acetoxy-3-tosylpent-4-enoates were afforded in moderate to good yields in a one-pot manner under mild conditions. This annulation reaction provides a highly efficient method to construct dinitrogen-fused heterocycles and ethyl (Z)-3-acetoxy-3-tosylpent-4-enoates at the same time.
- Lei, Yu,Xing, Jiao-Jiao,Xu, Qin,Shi, Min
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supporting information
p. 3486 - 3490
(2016/07/28)
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- Highly efficient and chemoselective zinc-catalyzed hydrosilylation of esters under mild conditions
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A mild and highly efficient catalytic hydrosilylation protocol for room-temperature ester reductions has been developed using diethylzinc as the catalyst. The methodology is operationally simple, displays high functional group tolerance and provides for a facile access to a broad range of different alcohols in excellent yields.
- Kovalenko, Oleksandr O.,Adolfsson, Hans
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p. 2785 - 2788
(2015/02/05)
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- A Phosphine-Catalyzed Novel Asymmetric [3+2] Cycloaddition of C,N-Cyclic Azomethine Imines with δ-Substituted Allenoates
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Catalytic asymmetric [3+2] cycloadditions of C,N-cyclic azomethine imines with δ-substituted allenoates have been developed in the presence of (S)-Me-f-KetalPhos, affording functionalized tetrahydroquinoline frameworks in good yields with high diastereo- and good enantioselectivities under mild condition. The substrate scope has been also examined. This is the first time that δ-substituted allenoates have been applied as a δ,γ-C-C bond participated C 2 synthon in asymmetric synthesis. Another round: Catalytic asymmetric [3+2] cycloaddition of C,N-cyclic azomethine imines with δ-substituted allenoates have been developed in the presence of (S)-Me-f-KetalPhos, affording functionalized tetrahydroquinoline frameworks in good yields with high diastereo- and good enantioselectivities under mild conditions. This is the first example applying δ-substituted allenoates as C 2 synthons in asymmetric δ,γ-C-C bond formation.
- Wang, De,Lei, Yu,Wei, Yin,Shi, Min
-
supporting information
p. 15325 - 15329
(2016/02/18)
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- Unusually Broad Substrate Profile of Self-Sufficient Cytochrome P450 Monooxygenase CYP116B4 from Labrenzia aggregata
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A new member of the CYP116B subfamily - P450LaMO - was discovered in Labrenzia aggregata by genomic data mining. It was successfully overexpressed in Escherichia coli, purified, and subsequently characterized spectroscopically, and its catalytic properties were assessed. Substrate profiling of the P450LaMO revealed that it was a versatile catalyst, exhibiting hydroxylation and epoxidation activities as well as O-dealkylation and asymmetric sulfoxidation activities. Diverse compounds, including alkylbenzenes, aromatic bicyclic molecules, and terpenoids, were shown to be hydroxylated by P450LaMO. Such diverse catalytic activities are uncommon for the bacterial P450s, and the P450LaMO -mediated stereoselective hydroxylation of inactivated C - H bonds - ubiquitous and relatively unreactive in organic molecules - is particularly unusual. The self-sufficient nature of P450LaMO, coupled with its broad substrate range, highlights it as an ideal template for directed evolution towards various applications.
- Yin, Yue-Cai,Yu, Hui-Lei,Luan, Zheng-Jiao,Li, Ren-Jie,Ouyang, Peng-Fei,Liu, Jing,Xu, Jian-He
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p. 2443 - 2449
(2015/03/03)
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- Unusually Broad Substrate Profile of Self-Sufficient Cytochrome P450 Monooxygenase CYP116B4 from Labrenzia aggregata
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A new member of the CYP116B subfamily - P450LaMO - was discovered in Labrenzia aggregata by genomic data mining. It was successfully overexpressed in Escherichia coli, purified, and subsequently characterized spectroscopically, and its catalytic properties were assessed. Substrate profiling of the P450LaMO revealed that it was a versatile catalyst, exhibiting hydroxylation and epoxidation activities as well as O-dealkylation and asymmetric sulfoxidation activities. Diverse compounds, including alkylbenzenes, aromatic bicyclic molecules, and terpenoids, were shown to be hydroxylated by P450LaMO. Such diverse catalytic activities are uncommon for the bacterial P450s, and the P450LaMO -mediated stereoselective hydroxylation of inactivated C-H bonds - ubiquitous and relatively unreactive in organic molecules - is particularly unusual. The self-sufficient nature of P450LaMO, coupled with its broad substrate range, highlights it as an ideal template for directed evolution towards various applications.
- Yin, Yue-Cai,Yu, Hui-Lei,Luan, Zheng-Jiao,Li, Ren-Jie,Ouyang, Peng-Fei,Liu, Jing,Xu, Jian-He
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p. 2443 - 2449
(2015/08/24)
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- Temporal separation of catalytic activities allows anti-Markovnikov reductive functionalization of terminal alkynes
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There is currently great interest in the development of multistep catalytic processes in which one or several catalysts act sequentially to rapidly build complex molecular structures. Many enzymes - often the inspiration for new synthetic transformations - are capable of processing a single substrate through a chain of discrete, mechanistically distinct catalytic steps. Here, we describe an approach to emulate the efficiency of these natural reaction cascades within a synthetic catalyst by the temporal separation of catalytic activities. In this approach, a single catalyst exhibits multiple catalytic activities sequentially, allowing for the efficient processing of a substrate through a cascade pathway. Application of this design strategy has led to the development of a method to effect the anti-Markovnikov (linear-selective) reductive functionalization of terminal alkynes. The strategy of temporal separation may facilitate the development of other efficient synthetic reaction cascades.
- Li, Le,Herzon, Seth B.
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- Selective switchable iron-catalyzed hydrosilylation of carboxylic acids
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Selective reduction of carboxylic acids either to aldehydes or alcohols is achieved using a one pot procedure based on iron-catalyzed hydrosilylations. Using phenylsilane and (COD)Fe(CO)3 catalyst under UV-irradiation at rt, alcohols were obtained specifically in good yields, whereas aldehydes were selectively obtained using TMDS and (t-PBO)Fe(CO)3 catalyst under thermal activation.
- Misal Castro, Luis C.,Li, Haoquan,Sortais, Jean-Baptiste,Darcel, Christophe
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supporting information
p. 10514 - 10516,3
(2020/09/02)
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- Regioselective synthesis of substituted naphthalenes and phenanthrenes by FeCl3-promoted annulation of aryl and naphthyl acetaldehydes with alkynes
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The FeCl3-promoted annulation reaction of aryl acetaldehydes with alkynes has been established, which provides a new and versatile straightforward procedure for the regioselective synthesis of mono-, di-, and polysubstituted naphthalenes under mild conditions. Interestingly, the present catalytic system not only differentiates between internal and terminal alkynes but also shows unprecedented complete Me3SiOH elimination selectivity for silyl alkyne substrates. Furthermore, the synthesis of a series of substituted phenanthrenes via reactions of nathphyl acetaldehydes with internal alkynes is also achieved for the first time in good yields with excellent regioselectivity.
- Bu, Xiuli,Hong, Longcheng,Liu, Ruiting,Hong, Jianquan,Zhang, Zhengxing,Zhou, Xigeng
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experimental part
p. 7960 - 7965
(2012/09/21)
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- CATALYTIC ANTI-MARKOVNIKOV OXIDATION AND HYDRATION OF OLEFINS
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The disclosure provides a dual-catalysis system for direct conversion of olefins to alcohols. The cooperative catalytic system contains one oxidizing catalyst and one transfer-hydrogenation catalyst. A wide variety of olefins, including aromatic and aliphatic olefins, can be used as the reactant. The transformation proceeds with anti-Markovnikov selectivity, and in some aspects provides primary alcohols as major products. The disclosure further provides a system for oxidation of olefins with anti-Markovnikov selectivity.
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Page/Page column 15
(2012/07/14)
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- Iron-catalyzed hydrosilylation of esters
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The first hydrosilylation of esters catalyzed by a well defined iron complex has been developed. Esters are converted to the corresponding alcohols at 100 °C, under solvent-free conditions and visible light activation. Copyright
- Bezier, David,Venkanna, Gopaladasu T.,Castro, Luis C. Misal,Zheng, Jianxia,Roisnel, Thierry,Sortais, Jean-Baptiste,Darcel, Christophe
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supporting information; experimental part
p. 1879 - 1884
(2012/09/22)
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- Enantioselective hydrosilylation of aromatic alkenes catalyzed by chiral bis(oxazolinyl)phenyl-rhodium acetate complexes
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Highly efficient and enantioselective hydrosilylation of aromatic alkenes catalyzed by the chiral rhodium acetate complexes with the bis(oxazolinyl)phenyl ligands has been reported that afforded chiral silane derivatives with up to 99% ee. Georg Thieme Ve
- Naito, Tatsuo,Yoneda, Takuma,Ito, Jun-Ichi,Nishiyama, Hisao
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p. 2957 - 2960
(2013/02/22)
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- Regioselective reductive hydration of alkynes to form branched or linear alcohols
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The regioselective reductive hydration of terminal alkynes using two complementary dual catalytic systems is described. Branched or linear alcohols are obtained in 75-96% yield with ?25:1 regioselectivity from the same starting materials. The method is compatible with terminal, di-, and trisubstituted alkenes. This reductive hydration constitutes a strategic surrogate to alkene oxyfunctionalization and may be of utility in multistep settings.
- Li, Le,Herzon, Seth B.
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supporting information
p. 17376 - 17379,4
(2020/09/16)
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- Microwave-assisted synthesis of 5-substituted 2-aminothiophenes starting from arylacetaldehydes
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An easy three-step pathway for the synthesis of arylacet-aldehydes from the corresponding carboxylic acids in very high yields is described. Their use as precursors of 5-substituted-2-aminothiophenes is illustrated via a microwave-assisted Gewald reaction. This method allows obtaining the expected compounds in a shorter time and with better yields and purities than the classical procedures. Georg Thieme Verlag Stuttgart - New York.
- Revelant, Germain,Dunand, Sandrine,Hesse, Stephanie,Kirsch, Gilbert
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p. 2935 - 2940
(2011/11/01)
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- Primary alcohols from terminal olefins: Formal anti-Markovnikov hydration via triple relay catalysis
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Alcohol synthesis is critical to the chemical and pharmaceutical industries. The addition of water across olefins to form primary alcohols (anti-Markovnikov olefin hydration) would be a broadly useful reaction but has largely proven elusive; an indirect hydroboration/oxidation sequence requiring stoichiometric borane and oxidant is currently the most practical methodology. Here, we report a more direct approach with the use of a triple relay catalysis system that couples palladium-catalyzed oxidation, acid-catalyzed hydrolysis, and ruthenium-catalyzed reduction cycles. Aryl-substituted terminal olefins are converted to primary alcohols by net reaction with water in good yield and excellent regioselectivity.
- Dong, Guangbin,Teo, Peili,Wickens, Zachary K.,Grubbs, Robert H.
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scheme or table
p. 1609 - 1612
(2012/02/01)
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- One-pot system for reduction of epoxides using NaBH4, PdCl 2 catalyst, and moist alumina
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Reduction of epoxides with sodium borohydride, a catalytic amount of palladium(II) chloride, and chromatographic neutral alumina preloaded with a small amount of water (moist alumina) in hexane gave alcohols in good to excellent yields and good selectivity of the desired products under mild conditions. The reaction system was operationally simple and environmentally friendly. The alumina can be recovered simply and reused a number of times without any treatment and with good activity.
- Yakabe, Shigetaka
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experimental part
p. 1339 - 1344
(2010/06/21)
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- AMINE COMPOUND AND PHARMACEUTICAL USE THEREOF
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Provided is a novel amine compound represented by the following formula (I) having a superior peripheral blood lymphocyte decreasing action and superior in the immunosuppressive action, rejection suppressive action and the like, which shows decreased side effects of, for example, bradycardia and the like, or a pharmaceutically acceptable acid addition salt thereof, or a hydrate thereof, or a solvate thereof. wherein each symbol is as defined in the specification.
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Page/Page column 80
(2010/04/25)
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- Enantiopure trans -3-arylaziridine-2-carboxamides: Preparation by bacterial hydrolysis and ring-openings toward enantiopure, unnatural D -α-amino acids
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Several racemic trans-3-arylaziridine-2-carboxamides were prepared and then resolved by Rhodococcus rhodochrous IFO 15564-catalyzed hydrolysis. The resulting enantiopure (2R,3S)-3-arylaziridine-2-carboxamides are adequate substrates to undergo fully stereoselective nucleophilic ring-openings at the C-3 ring position to finally yield enantiopure, unnatural d-α- aminocarboxylic acids. Experimental evidence is provided that suggests the fate of the (2S,3R)-3-arylaziridine-2-carboxylic acids concomitantly formed during the resolution processes. In this context, the similar bacterial resolution of racemic 1-arylaziridine-2-carboxamides and -carbonitriles, previously investigated by our research group, has been partially re-examined.
- Moran-Ramallal, Roberto,Liz, Ramon,Gotor, Vicente
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supporting information; experimental part
p. 6614 - 6624
(2010/11/17)
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- Enantioselective epoxidation of nonconjugated cis-olefins by chiral dioxirane
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A variety of nonconjugated cis-olefins has been enantioselectively epoxidized with chiral ketones 2, and up to 92% ee has been obtained. The two prochiral faces of an olefin are likely stereodifferentiated by the relative hydrophobicity of the olefin substituents and/or allylic oxygen functionality.
- Burke, Christopher P.,Shi, Yian
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supporting information; experimental part
p. 5150 - 5153
(2009/12/28)
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- An improved bouveault-blanc ester reduction with stabilized alkali metals
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Significantly improved Bouveault-Blanc conditions for ester reduction have been developed using sodium in silica gel (Na-SG), a free-flowing powder that can be easily handled in the open atmosphere. Primary alcohols were prepared in excellent yield from a variety of aliphatic esters under mild reaction conditions. The chemistry presented here is far safer than the classic Bouveault-Blanc reduction and is competitive with more modern hydride reduction methods.
- Bodnar, Brian S.,Vogt, Paul F.
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supporting information; experimental part
p. 2598 - 2600
(2009/08/07)
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- The mechanism for the rhodium-catalyzed decarbonylation of aldehydes: A combined experimental and theoretical study
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The mechanism for the rhodium-catalyzed decarbonylation of aldehydes was investigated by experimental techniques (Hammett studies and kinetic isotope effects) and extended by a computational study (DFT calculations). For both benzaldehyde and phenyl acetaldehyde derivatives, linear Hammett plots were obtained with positive slopes of +0.79 and +0.43, respectively, which indicate a buildup of negative charge in the selectivity-determining step. The kinetic isotope effects were similar for these substrates (1.73 and 1.77 for benzaldehyde and phenyl acetaldehyde, respectively), indicating that similar mechanisms are operating. A DFT (B3LYP) study of the catalytic cycle indicated a rapid oxidative addition into the C(O)-H bond followed by a rate-limiting extrusion of CO and reductive elimination. The theoretical kinetic isotope effects based on this mechanism were in excellent agreement with the experimental values for both substrates, but only when migratory extrusion of CO was selected as the rate-determining step.
- Fristrup, Peter,Kreis, Michael,Palmelund, Anders,Norrby, Per-Ola,Madsen, Robert
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p. 5206 - 5215
(2008/12/22)
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- Design and synthesis of phenethyl benzo[1,4]oxazine-3-ones as potent inhibitors of PI3Kinaseγ
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The Type 1 PI3Kinases comprise a family of enzymes, which primarily phosphorylate PIP2 to give the second messenger PIP3, a key player in many intracellular signaling processes [Science, 2002, 296, 1655; Trends Pharmacol. Sci. 2003, 24, 366]. Of the four type 1 PI3Ks, the γ-isoform, which is expressed almost exclusively in leukocytes [Curr. Biol., 1997, 7, R470], is of particular interest with respect to its role in inflammatory diseases such as rheumatoid arthritis (RA) and chronic obstructive pulmonary disease (COPD) [Mol. Med. Today, 2000, 6, 347]. Investigation of a series of 4,6-disubstituted-4H-benzo[1,4]oxazin-3-ones has led to the identification of single-digit nanomolar inhibitors of PI3Kγ, several of which had good cell based activity and were shown to be active in vivo in an aspectic peritonitis model of inflammatory cell migration.
- Lanni Jr., Thomas B.,Greene, Keri L.,Kolz, Christine N.,Para, Kimberly S.,Visnick, Melean,Mobley, James L.,Dudley, David T.,Baginski, Theodore J.,Liimatta, Marya B.
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p. 756 - 760
(2007/10/03)
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- METHOD AND COMPOUNDS FOR RNA SYNTHESIS
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The 2-(4-tolylsulfonyl)ethoxymethyl (TEM) as a new 2'-OH protecting group is reported for the RNA synthesis on the solid support using the phosphoramidite chemistry. The usefulness of the 2'-0-TEM group is exemplified by the synthesis of 12 different oligo-RNAs of various sizes (14-38nt long). The stepwise coupling yield varied from 97 - 99 % with an optimized coupling time of 120s. Synthesis of all four pure phosphoramidite building blocks are also described. Two new reliable parameters, δc2' - δc3s and δn2' - δH3' have been suggested for the characterization of isomeric 2'-0-TEM and 3'-0-TEM as well as other isomeric mono 273 '-protected ribonucleoside derivatives. The most striking feature of this strategy is that the crude RNA prepared using our 2'-0-TEM strategy is sufficiently pure (>90 %) for molecular biology research without any additional purification step, thereby making oligo-RNAs easily available at a relatively low cost, saving both time and lab resources.
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Page/Page column 17
(2010/11/27)
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- [1,2]-Wittig rearrangement from chloromethyl ethers
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The reaction of different chloromethyl ethers 1 with an excess of lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (2.5 mol %) in THF at 0 °C leads to the corresponding α-lithiomethyl ether intermediates, through a chlorine-lithium exchange, which spontaneously undergo a clean [1,2]-Wittig rearrangement affording the expected homobenzylic alcohols 2. This is the first version of this rearrangement starting from easily available chloromethyl ethers.
- Gómez, Cecilia,Maciá, Beatriz,Lillo, Victor J.,Yus, Miguel
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p. 9832 - 9839
(2007/10/03)
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- TADDOL-derived phosphites and phosphoramidites for efficient rhodium-catalyzed asymmetric hydroboration
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Two simple TADDOL-derived monodentate ligands, the (1R,2S)-2- phenylcyclohexanol-derived phosphite and the N,N-(phenylbenzyl)-phosphoramidite, give comparably high levels of enantioselectivity (90-96% ee) in the rhodium-catalyzed hydroborations of substituted styrenes bearing either electron-donating or electron-withdrawing substituents. Rhodium(I) chloride and tetrafluoroborate catalyst precursors give comparable results. Pinacolborane is superior to catecholborane in these reactions.
- Moteki, Shin A.,Wu, Di,Chandra, Kusum L.,Sahadeva Reddy,Takacs, James M.
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p. 3097 - 3100
(2007/10/03)
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- Intramolecular C-N bond formation reactions catalyzed by ruthenium porphyrins: Amidation of sulfamate esters and aziridination of unsaturated sulfonamides
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Ruthenium porphyrins [Ru(F20-TPP)(CO)] (F20-TPP = 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato dianion) and [Ru(Por*)(CO)] (Por* = 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5, 8-dimethanoanthracen-9-yl]porphyrinato dianion) catalyzed intramolecular amidation of sulfamate esters p-X-C6H4(CH 2)2OSO2NH2 (X = Cl, Me, MeO), XC6H4(CH2)3OSO2NH 2 (X = p-F, p-MeO, m-MeO), and Ar(CH2)2OSO 2NH2 (Ar = naphthalen-1-yl, naphthalen-2-yl) with PhI(OAc)2 to afford the corresponding cyclic sulfamidates in up to 89% yield with up to 100% substrate conversion; up to 88% ee was attained in the asymmetric intramolecular amidation catalyzed by [Ru(Por*)(CO)]. Reaction of [Ru(F20-TPP)(CO)] with PhI=NSO2OCH 2CCl3 (prepared by treating the sulfamate ester Cl 3CCH2OSO2NH2 with PhI(OAc) 2) afforded a bis(imido)ruthenium(VI) porphyrin, [Ru VI(F20-TPP)(NSO2OCH2CCl 3)2], in 60% yield. A mechanism involving reactive imido ruthenium porphyrin intermediate was proposed for the ruthenium porphyrin-catalyzed intramolecular amidation of sulfamate esters. Complex [Ru(F20-TPP)(CO)] is an active catalyst for intramolecular aziridination of unsaturated sulfonamides with PhI(OAc)2, producing corresponding bicyclic aziridines in up to 87% yield with up to 100% substrate conversion and high turnover (up to 2014).
- Liang, Jiang-Lin,Yuan, Shi-Xue,Huang, Jie-Sheng,Che, Chi-Ming
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p. 3610 - 3619
(2007/10/03)
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- ZnI2/NaCNBH3 as an Efficient Reagent for Regioselective Ring Opening of the Benzylic Epoxide Moiety
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In the presence of zinc iodide, sodium cyanoborohydride was found to produce regioselective ring opening of benzylic epoxides in mild reaction conditions.
- Finkielsztein,Aguirre,Lantano,Alesso,Moltrasio Iglesias
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p. 895 - 901
(2007/10/03)
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- Negishi-type coupling of bromoarenes with dimethylzinc
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Treatment of bromoarenes with dimethylzinc in the presence of a palladium catalyst provides a high-yielding route to methylarenes. The process accommodates a wide range of aromatic substituents and, in the majority of cases, is free of side reactions.
- Herbert, John M.
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p. 817 - 819
(2007/10/03)
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- Regio- and enantiocontrol in the room-temperature hydroboration of vinyl arenes with pinacol borane
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The catalyzed hydroboration of vinyl arenes was carried out using pinacol borane instead of catechol borane, as the former reagent and the product boronates are significantly easier to handle. By careful choice of catalyst, either the branched or the linear product can be obtained in greater than 96% selectivity. Interestingly, common ligands such as BINAP and Josiphos give opposite asymmetric induction with pinacol borane as compared with catechol borane, while P,N-ligands such as Quinap gave the same sense of induction. The hydroboration of 6-methoxynaphthalene proceeded with the greatest regio- (95:5) and enantioselectivity (94:6) of all vinyl arenes examined. The hydroboration product was then employed in a concise synthesis of the nonsteroidal antiinflammatory agent, Naproxen. Copyright
- Crudden, Cathleen M.,Hleba, Yonek B.,Chen, Austin C.
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p. 9200 - 9201
(2007/10/03)
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- Readily available biaryl P,N ligands for asymmetric catalysis
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A short and modular synthesis of novel P,N ligands (pinap; see scheme; X = O or NH) is presented. A covalently bound chiral group allows the separation of the atropisomeric diastereomers, thus avoiding resolution involving chiral Pd-amine complexes. The utility of the ligands is demonstrated for three reactions catalyzed by different transition metals; in each case products are obtained with high enantiomeric excess (up to 99% ee).
- Knoepfel, Thomas F.,Aschwanden, Patrick,Ichikawa, Takashi,Watanabe, Takumi,Carreira, Erick M.
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p. 5971 - 5973
(2007/10/03)
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- Method of producing heterocylic carbamates from aza-heterocyclic compounds and carbon dioxide
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The invention relates to a method of producing heterocyclic carbamates of the general formula (I) by reacting aza-heterocyclic compounds with alkyl- or aryl-halides in the presence of carbon dioxide and alkali carbonate, and to new compounds of the general formula (I).
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- Novel ruthenium complexes and process for preparing alcoholic compounds using these
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The invention provides novel ruthenium complexes having an optically active diphosphine compound, which has asymmetry on carbon and is easy to synthesize, as the ligand and a process for preparing optically active alcoholic compounds using said complexes as the catalysts, wherein said process is the process for preparing optically active alcoholic compounds, which are excellent in terms of reactivity, enatioselectivity and the like in an asymmetric hydrogenation of carbonyl compounds compared with conventional ruthenium complex catalysts having an optically active diphosphine compound having the axial chirality or the asymmetry on carbon as the ligand. In a preferred embodiment, the invention provides an optically active ruthenium complex represented by the general formula (1) 1wherein X and Y, which can be identical to or different from each other, represent a hydrogen atom or an anion group, R1 and R2, which can be identical to or different from each other, represent a chain or cyclic hydrocarbon group of carbon number 1 to 20, which can be substituted, R3 and R4, which can be identical to or different from each other, represent a hydrogen atom or a hydrocarbon group of carbon number 1 to 3, and R5, R6, R7 and R8, which can be identical to or different from one another, represent a hydrocarbon group of carbon number 1 to 30, which can be substituted, with the proviso that when X and Y are bromine, R1 and R2 are a methyl group, and when R3 and R4 are a hydrogen atom, at least one of R5, R6, R7 and R8is not a phenyl group.
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- Oxidation of Carbon-Silicon Bonds: The Dramatic Advantage of Strained Siletanes
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(Matrix presented) Herein we report on the use of siletanes as substrates for the oxidation of carbon-silicon bonds. These tetraalkylsilanes are easy to handle yet susceptible to rapid ring opening and oxidation upon exposure to aqueous fluoride and peroxide. This combination of stability and reactivity presents many practical benefits, including compatibility with silicon protecting groups and electron-rich aromatic rings.
- Sunderhaus, James D.,Lam, Hubert,Dudley, Gregory B.
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p. 4571 - 4573
(2007/10/03)
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- The scope of catalytic asymmetric hydroboration/oxidation with rhodium complexes of 1,1'-(2-diarylphosphino-1-naphthyl)isoquinolines
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Preformed cationic Rh complexes of the title ligands are effective for the asymmetric hydroboration/oxidation of vinylarenes at ambient temperature. These vinylarenes may carry E- or Z-β substituents but not a substituents. Enantiomer excesses of up to 97% can be obtained in the most favourable cases. The enantioselectivity is moderately sensitive to the structure of the ligand: the difurylphosphino ligand gave superior results for electron-poor styrenes and the diphenylphosphino ligand the best results for electron-rich reactants. Mechanistic aspects are discussed.
- Doucet, Henri,Fernandez, Elena,Layzell, Timothy P.,Brown, John M.
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p. 1320 - 1330
(2007/10/03)
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- Stereochemical control in microbial reduction. Part 31: Reduction of alkyl 2-oxo-4-arylbutyrates by baker's yeast under selected reaction conditions
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Treatment of baker's yeast with phenacyl chloride in an aqueous-organic solvent has been proven to be an effective method of inhibiting the enzymes that afford (S)-enantiomers of α-hydroxy esters in the reduction of α-keto esters. The procedure is effective for the whole-cell system to produce the (R)-product with high chemical yield and high enantiomeric excess.
- Dao, Duc Hai,Okamura, Mutsuo,Akasaka, Takeshi,Kawai, Yasushi,Hida, Kouichi,Ohno, Atsuyoshi
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p. 2725 - 2737
(2007/10/03)
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- Catalytic ethylation of phenols
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Alkylation of phenol and cresols with ethanol in the presence of iron-aluminum catalyst was studied.
- Agaev,Shakhtakhtinskaya,Eminov,Guliev
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p. 651 - 653
(2007/10/03)
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- True metal-catalyzed hydroboration with titanium
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Dicarbonyltitanocene is an efficient and highly selective catalyst for alkyne hydroborations by catecholborane and dimethyltitanocene is an efficient and highly selective catalyst for alkene hydroborations. These results contrast the hydroboration chemistry with other early transition metal complexes that simply lead to decomposition of catecholborane to form diborane and parallel the hydroboration chemistry of permethylcyclopentadienyl lanthanide complexes. Titanocene dicarbonyl leads to exclusive anti-Markovnikov regiochemistry and to exclusive single additions of catecholborane across alkynes. Dimethyltitanocene leads to predominantly anti-Markovnikov regiochemistry with alkyl-substituted olefins, and exclusive anti-Markovnikov regiochemistry with vinylarenes. Two titanium(III) complexes, Cp2Ti(H2Bcat) and Cp2Ti(Bcat2), were isolated from the reaction mixtures. These Ti(III) complexes, as well as [Cp2TiH]2 and [Cp2TiMe]2, catalyze the addition of catecholborane to olefins more slowly than the titanium(II) and titanium(IV) compounds. These results are rationalized by a σ bond metathsis between catecholborane and titanocene alkene and alkyne complexes that possess metallacyclopropane and metallacyclopropene character as the B-C bond-forming step. This B-C bond-forming step of the catalysis was observed directly in model reactions.
- He, Xiaoming,Hartwig, John F.
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p. 1696 - 1702
(2007/10/03)
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- Studies on the Regioselectivities in the Oxidation of Simple Alkyl Aromatic Hydrocarbons by Molecular Oxygen
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The products of the autoxidation of various simple alkyl aromatic hydrocarbons were reduced by LiAlH4, and the alcohols formed were determined by gas chromatography.In the cases of 2-phenylbutane, 3-phenylpentane, and 2-p-tolylbutane a considerable fragmentation of the intermediate tertiary alkoxy radicals was proved.On the basis of the analytical results relative reaction rates of the various C-H bonds in the hydrocarbons studied were calculated.It is shown that the attack at C-H bonds which are not activated by the aromatic nucleus cannot be neglected and may be of great importance for the kinetics of the oxidation of alkyl aromatic hydrocarbons.
- Pritzkow, Wilhelm,Thomas, Gerda,Willecke, Lothar
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p. 847 - 851
(2007/10/02)
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- FUNGAL HYDROXYLATION OF ETHYL BENZENE AND DERIVATIVES
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The fungus Mortierella isabellina converts ethyl benzene and a number of para-substituted derivatives to the corresponding optically active 1-phenylethanols with enantiomeric excesses between 5 and 40percent.Hydrogen removal from the substrate preceeds product formation and is stereochemically independent of it.
- Holland, Herbert L.,Carter, Ian M.,Chenchaiah, P. Chinna,Khan, Shaheer H.,Munoz, Benito,et al.
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p. 6409 - 6412
(2007/10/02)
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- Substituent Effects on the Intramolecular Photochemical Reactions of Phenyl-Ethenyl Non-conjugated Bichromophoric Systems
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The effects of substitution on the photochemistry of phenyl-ethenyl bichromophoric systems are reported.Methyl substitution at the 2-, 3-, 5-, and 1,1,2-positions in the pentene moiety of 5-phenylpent-1-ene reduces both reaction efficiency and selectivity but in contrast to intramolecular analogues the photoreaction of 3-phenethylcyclohexene is comparable with that of the corresponding cyclopentene.Incorporation of ester units in the connecting unit between the chromophores or on the ethene inhibits intramolecular cyclisation as does the presence of para OMe, CN, or COMe groups in 5-phenylpent-1-ene.In contrast reaction selectivity and efficiency are greatly promoted by ortho Me or OMe groups and the products reflect exlusive 1,3-cycloaddition.The presence of a para Me group in 5-phenylpent-1-ene leads to specific 2,6-intramolecular cyclisation but the reaction of the meta-Me derivative leads to four products derived from 1,3- and 1,5-intramolecular cycloaddition.The observations are discussed in terms of mechanisms of arene-ethene photoreactions and preferred conformations of the bichromophores.
- Ellis-Davies, Graham C. R.,Gilbert, Andrew,Heath, Peter,Lane, Jon C.,Warrington, John V.,Westover, David L.
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p. 1833 - 1842
(2007/10/02)
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