- syn-Selective Michael Reaction of α-Branched Aryl Acetaldehydes with Nitroolefins Promoted by Squaric Amino Acid Derived Bifunctional Br?nsted Bases
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Here we describe a direct access to 2,2,3-trisubstituted syn γ-nitroaldehydes by addition of α-branched aryl acetaldehydes to nitroolefins promoted by a cinchona based squaric acid-derived amino acid peptide. Different α-methyl arylacetaldehydes react with β-aromatic and β-alkyl nitroolefins to afford the Michael adducts in high enantioselectivity and syn-selectivity. NMR experiments and DFT calculations predict the reaction to occur through the intermediacy of E-enolate. The interaction between the substrates and the catalyst follows Pápai's model, wherein an intramolecular H-bond interaction in the catalyst between the NH group of one of the tert-leucines and the squaramide oxygen seems to be key for discrimination of the corresponding reaction transition states.
- Campano, Teresa E.,García-Urricelqui, Ane,Mielgo, Antonia,Palomo, Claudio,de Cózar, Abel
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supporting information
p. 3604 - 3612
(2021/07/26)
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- Combined Theoretical and Experimental Studies Unravel Multiple Pathways to Convergent Asymmetric Hydrogenation of Enamides
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We present a highly efficient convergent asymmetric hydrogenation of E/Z mixtures of enamides catalyzed by N,P-iridium complexes supported by mechanistic studies. It was found that reduction of the olefinic isomers (E and Z geometries) produces chiral amides with the same absolute configuration (enantioconvergent hydrogenation). This allowed the hydrogenation of a wide range of E/Z mixtures of trisubstituted enamides with excellent enantioselectivity (up to 99% ee). A detailed mechanistic study using deuterium labeling and kinetic experiments revealed two different pathways for the observed enantioconvergence. For α-aryl enamides, fast isomerization of the double bond takes place, and the overall process results in kinetic resolution of the two isomers. For α-alkyl enamides, no double bond isomerization is detected, and competition experiments suggested that substrate chelation is responsible for the enantioconvergent stereochemical outcome. DFT calculations were performed to predict the correct absolute configuration of the products and strengthen the proposed mechanism of the iridium-catalyzed isomerization pathway.
- Ahlquist, M?rten S. G.,Andersson, Pher G.,Eriksson, Lars,Krajangsri, Suppachai,Massaro, Luca,Ponra, Sudipta,Silvi, Emanuele,Singh, Thishana,Su, Hao,Yang, Jianping
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supporting information
p. 21594 - 21603
(2021/12/27)
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- Copper-catalyzed hydroformylation and hydroxymethylation of styrenes
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Hydroformylation catalyzed by transition metals is one of the most important homogeneously catalyzed reactions in industrial organic chemistry. Millions of tons of aldehydes and related chemicals are produced by this transformation annually. However, most of the applied procedures use rhodium catalysts. In the procedure described here, a copper-catalyzed hydroformylation of alkenes has been realized. Remarkably, by using a different copper precursor, the aldehydes obtained can be further hydrogenated to give the corresponding alcohols under the same conditions, formally named as hydroxymethylation of alkenes. Under pressure of syngas, various aldehydes and alcohols can be produced from alkenes with copper as the only catalyst, in excellent regioselectivity. Additionally, an all-carbon quaternary center containing ethers and formates can be synthesized as well with the addition of unactivated alkyl halides. A possible reaction pathway is proposed based on our results. This journal is
- Franke, Robert,Geng, Hui-Qing,Meyer, Tim,Wu, Xiao-Feng
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p. 14937 - 14943
(2021/12/02)
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- Highly efficient NHC-iridium-catalyzed β-methylation of alcohols with methanol at low catalyst loadings
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The methylation of alcohols is of great importance since a broad number of bioactive and pharmaceutical alcohols contain methyl groups. Here, a highly efficient β-methylation of primary and secondary alcohols with methanol has been achieved by using bis-N-heterocyclic carbene iridium (bis-NHC-Ir) complexes. Broad substrate scope and up to quantitative yields were achieved at low catalyst loadings with only hydrogen and water as by-products. The protocol was readily extended to the β-alkylation of alcohols with several primary alcohols. Control experiments, along with DFT calculations and crystallographic studies, revealed that the ligand effect is critical to their excellent catalytic performance, shedding light on more challenging Guerbet reactions with simple alcohols. [Figure not available: see fulltext.].
- Lu, Zeye,Zheng, Qingshu,Zeng, Guangkuo,Kuang, Yunyan,Clark, James H.,Tu, Tao
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p. 1361 - 1366
(2021/06/30)
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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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- Manganese-catalysed transfer hydrogenation of esters
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Manganese catalysed ester reduction using ethanol as a hydrogen transfer agent in place of dihydrogen is reported. High yields can be achieved for a range of substrates using 1 mol% of a Mn(i) catalyst, with an alkoxide promoter. The catalyst is derived from a tridentate P,N,N ligand.
- Oates, Conor L.,Widegren, Magnus B.,Clarke, Matthew L.
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supporting information
p. 8635 - 8638
(2020/08/21)
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- Iridium Complex-Catalyzed C2-Extension of Primary Alcohols with Ethanol via a Hydrogen Autotransfer Reaction
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The development of a C2-extension of primary alcohols with ethanol as the C2 source and catalysis by [Cp*IrCl2]2 (where Cp? = pentamethylcyclopentadiene) is described. This new extension system was used for a range of benzylic alcohol substrates and for aliphatic alcohols with ethanol as an alkyl reagent to generate the corresponding C2-extended linear alcohols. Mechanistic studies of the reaction by means of intermediates and deuterium labeling experiments suggest the reaction is based on hydrogen autotransfer.
- Kobayashi, Masaki,Itoh, Satoshi,Yoshimura, Keisuke,Tsukamoto, Yuya,Obora, Yasushi
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p. 11952 - 11958
(2020/10/23)
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- A is by aromatic carboxylic acid non-catalytic reaction of alcohol compound (by machine translation)
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The present invention discloses a non-catalytic reaction of the aromatic carboxylic acid preparation of alcohol compound. In an inert gas atmosphere, after dehydration and deoxidation treatment of the reaction bottle [...] borane and carboxylic acid stirring and mixing, reaction 6 - 12 hours to obtain borate, further hydrolyzed into alcohol; said carboxylic acid is benzoic acid, 4 - bromobenzoic acid, 4 - fluoro benzoic acid, 1 - naphthoic acid, 2 - methoxybenzene formic acid and the like. The invention for the first time in the absence of catalyst under the conditions of high-efficiently using carboxylic acid with borane generating borohydrite reaction, carbonyl compound with borane generating borohydrite reaction preparation borate, further hydrolysis alcohol, provides new programme. (by machine translation)
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Paragraph 0029
(2019/04/17)
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- Method for preparing alcoholic compound from anilino lithium compound as catalyst
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The invention relates to an application of an anilino lithium compound, in particular to a method for preparing an alcoholic compound from the anilino lithium compound as a catalyst. The catalyst, borane and carboxylic acid are stirred and mixed uniformly, subjected to a reaction and exposed to air to terminate the reaction, a reacted liquid is subjected to reduced-pressure treatment for solvent removal, silica gel and methanol are added, and the alcoholic compound is obtained by hydrolysis. The anilino lithium compound can perform high-activity catalysis on the reaction between carboxylic acid and borane at room temperature, dose of the catalyst is only 0.8mol% of the mole ratio of carboxylic acid, compared with the conventional catalysis system, the commercial reagent anilino lithium compound is used, reaction conditions are mild, and yield of borate with different substituents under limit conditions can reach 90% or higher.
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- Based on n-butyl aromatic carboxylic acid preparation of alcohol compound
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The present invention relates to n-butyl application, in particular to based on n-butyl aromatic carboxylic acid preparation of alcohol compound, the catalyst sequentially, borane and carboxylic acid uniformly stirred and mixed, exposed to the air after the reaction terminated in the reaction, the reaction solution under reduced pressure to remove the solvent, then adding silica gel methanol hydrolyzed to obtain the alcohol compound. The invention discloses a butyl lithium can be high activity under the room temperature condition of catalytic carboxylic acid and borane borohydride reaction, the catalyst levels are only the molar amount of carboxylic acid 0.5 μM %, compared with the prior catalytic system, using the commercial reagent is BuLi, mild reaction conditions, in under a limited condition of different substituents of the yield of the ester can reach 90% or more.
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- Highly Enantioselective Catalytic Kinetic Resolution of α-Branched Aldehydes through Formal Cycloaddition with Homophthalic Anhydrides
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A new catalytic methodology was developed to promote an efficient one-pot kinetic resolution of racemic aldehydes with selectivity (s*) of up to 91 (99:1 d.r., >99 % ee) in a cycloaddition reaction with enolizable anhydrides to afford dihydroisocoumarin products (a core prevalent in natural products and molecules of medicinal interest) containing three contiguous stereocentres.
- Farid, Umar,Aiello, Maria Luisa,Connon, Stephen J.
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supporting information
p. 10074 - 10079
(2019/07/18)
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- Generation and Application of (Diborylmethyl)zinc(II) Species: Access to Enantioenriched gem-Diborylalkanes by an Asymmetric Allylic Substitution
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We report the successful generation of (diborylmethyl)zinc(II) species by transmetallation beteween isolable (diborylmethyl)lithium and zinc(II) halide (X=Br, Cl) and their application in the synthesis of enantioenriched gem-diborylalkanes bearing a stereogenic center at the β-position of the diboryl groups by an asymmetric allylic substitution reaction. The reaction has a broad substrate scope, and various enantioenriched gem-diborylalkanes can be obtained in good yields with excellent enantioselectivity. Further elaboration of the enantioenriched gem-diborylalkanes provides access to a diverse set of valuable chiral building blocks.
- Lee, Yeosan,Park, Jinyoung,Cho, Seung Hwan
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p. 12930 - 12934
(2018/09/25)
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- Dual Rh?Ru Catalysts for Reductive Hydroformylation of Olefins to Alcohols
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An active and selective dual catalytic system to promote domino hydroformylation–reduction reactions is described. Apart from terminal, di- and trisubstituted olefins, for the first time the less active internal C?C double bond of tetrasubstituted alkenes can also be utilized. As an example, 2,3-dimethylbut-2-ene is converted into the corresponding n-alcohol with high yield (90 %) as well as regio- and chemoselectivity (>97 %). Key for this development is the use of a combination of Rh complexes with bulky monophosphite ligands and the Ru-based Shvo's complex. A variety of aromatic and aliphatic alkenes can be directly used to obtain mainly linear alcohols.
- Rodrigues, Fábio M. S.,Kucmierczyk, Peter K.,Pineiro, Marta,Jackstell, Ralf,Franke, Robert,Pereira, Mariette M.,Beller, Matthias
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p. 2310 - 2314
(2018/07/31)
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- TiO2-Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols
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TiO2-supported Re, Re/TiO2, was found to promote selective hydrogenation of carboxylic acids having aromatic and aliphatic moieties to the corresponding alcohols. Re/TiO2showed superior results compared to other transition-metal-loaded TiO2and supported Re catalysts for selective hydrogenation of 3-phenylpropionic acid. 3-phenylpropanol was produced in 97 % yield under mild conditions (5 MPa H2at 140 °C). Contrary to typical heterogeneous catalysts, Re/TiO2does not lead to the formation of dearomatized byproducts. The catalyst is recyclable and shows a wide substrate scope in the synthesis of alcohols (22 examples; up to 97 % isolated yield).
- Toyao, Takashi,Siddiki, S. M. A. Hakim,Touchy, Abeda S.,Onodera, Wataru,Kon, Kenichi,Morita, Yoshitsugu,Kamachi, Takashi,Yoshizawa, Kazunari,Shimizu, Ken-Ichi
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p. 1001 - 1006
(2017/02/05)
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- Design of Potent and Druglike Nonphenolic Inhibitors for Catechol O-Methyltransferase Derived from a Fragment Screening Approach Targeting the S-Adenosyl- l -methionine Pocket
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A fragment screening approach designed to target specifically the S-adenosyl-l-methionine pocket of catechol O-methyl transferase allowed the identification of structurally related fragments of high ligand efficiency and with activity on the described orthogonal assays. By use of a reliable enzymatic assay together with X-ray crystallography as guidance, a series of fragment modifications revealed an SAR and, after several expansions, potent lead compounds could be obtained. For the first time nonphenolic and small low nanomolar potent, SAM competitive COMT inhibitors are reported. These compounds represent a novel series of potent COMT inhibitors that might be further optimized to new drugs useful for the treatment of Parkinson's disease, as adjuncts in levodopa based therapy, or for the treatment of schizophrenia.
- Lerner, Christian,Jakob-Roetne, Roland,Buettelmann, Bernd,Ehler, Andreas,Rudolph, Markus,Sarmiento, Rosa María Rodríguez
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p. 10163 - 10175
(2016/12/07)
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- Ruthenium-catalyzed hydroformylation/reduction of olefins to alcohols: Extending the scope to internal alkenes
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In the presence of 2-phosphino-substituted imidazole ligands and Ru 3(CO)12 or Ru(methylallyl)2(COD) direct hydroformylation and hydrogenation of alkenes to alcohols takes place. In addition to terminal alkenes, also more challenging internal olefins are converted preferentially to industrially important linear alcohols in high yield (up to 88%) and regioselectivity (n:iso up to 99:1).
- Wu, Lipeng,Fleischer, Ivana,Jackstell, Ralf,Profir, Irina,Franke, Robert,Beller, Matthias
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supporting information
p. 14306 - 14312
(2013/10/21)
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- From olefins to alcohols: Efficient and regioselective ruthenium-catalyzed domino hydroformylation/reduction sequence
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Exploring the alternatives: Ruthenium imidazoyl phosphine complexes catalyze the domino hydroformylation/reduction of alkenes to alcohols in good yields and with good selectivities (see scheme). Linear aliphatic alcohols are synthesized under reaction conditions typically used in industrial hydroformylations. Copyright
- Fleischer, Ivana,Dyballa, Katrin Marie,Jennerjahn, Reiko,Jackstell, Ralf,Franke, Robert,Spannenberg, Anke,Beller, Matthias
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supporting information
p. 2949 - 2953
(2013/04/10)
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- Synthesis of alcohols via a rhodium-catalyzed hydroformylation-reduction sequence using tertiary bidentate amine ligands
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The synthesis of alcohols from aromatic olefins is described using a rhodium-catalyzed hydroformylation-reduction sequence with the assistance of a tertiary diamine ligand. The alcohols are produced in excellent branched to linear ratios and in good to excellent isolated yields. In all cases no aldehyde product, from hydroformylation, or alkyl product, from olefin reduction, was detected. Copyright
- Cheung, Lawrence L. W.,Vasapollo, Giuseppe,Alper, Howard
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supporting information; experimental part
p. 2019 - 2022
(2012/09/22)
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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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- Indium-catalyzed reductive esterification of a carboxylic acid: Sequential preparation of an ester and symmetrical ether
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An unprecedented reductive dimerization of two carboxylic acids to produce ester derivatives by a combination catalyst involving InBr3 and sulfuric acid is described. A sequential conversion of the in-situ formed ester to a symmetrical ether by indium-catalyzed deoxygenation of the ester with a hydrosilane in the same pot was also demonstrated. Copyright
- Sakai, Norio,Usui, Yuta,Ikeda, Reiko,Konakahara, Takeo
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supporting information; experimental part
p. 3397 - 3401
(2012/02/02)
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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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- Remarkable Change of the Diastereoselection in the Dye-Sensitized Ene Hydroperoxidation of Chiral Alkenes by Zeolite Confinement
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(Equation presented) The ene reaction of singlet oxygen with chiral trisubstituted alkenes bearing an alkyl and a phenyl group at the stereogenic center is erythro diastereoselective in solution and threo diastereoselective if carried out within zeolite Na-Y. The change of the diastereoselection trend by zeolite confinement is attributed to a synergism of steric effects and cation-π interactions.
- Stratakis, Manolis,Kalaitzakis, Dimitris,Stavroulakis, Dimitris,Kosmas, Giannis,Tsangarakis, Constantinos
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p. 3471 - 3474
(2007/10/03)
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- Lewis base-catalyzed addition of trialkylaluminum compounds to epoxides
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A novel concept for catalytic epoxide alkylation has been developed. Lewis bases like phosphanes, arsanes, stibanes, and sulfides were found to catalyze the alkylation of symmetrical epoxides with trialkylaluminum compounds very effectively at a 5 mol % level. Cyclic as well as acyclic epoxides were readily alkylated in good yields. In reactions with terminal epoxides a significant enhancement of rate and/or regioselectivity was noted in the Lewis base-catalyzed process. Coordination of the Lewis base to the Lewis acidic aluminum reagent was proved by 27Al and 31p NMR spectroscopy and is proposed to form a more nucleophilic alkylating agent.
- Schneider, Christoph,Brauner, J?rg
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p. 4445 - 4450
(2007/10/03)
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- Regioselective Metallation of Propylbenzene with Superbase: A Convenient Route to Stilbene Derivatives
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The benzylic metallation of propylbenzene has been elaborated with LIC-KOR superbase; the method has been applied in a new synthesis of stilbene derivatives.
- Thurner, Angelika,Agai, Bela,Faigl, Ferenc
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p. 158 - 159
(2007/10/03)
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- An Air-Stable Catalyst System for the Conversion of Esters to Alcohols
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The combination of 5 mol percent of Ti(O-i-Pr)4 with 2.5-3.0 equiv (EtO)3SiH cleanly hydrosilylates esters to silyl ethers at 40-55 deg C, which can be converted to the corresponding primary alcohols via aqueous alkaline hydrolysis in excellent overall yield.The reaction can be carried out in the air, without solvent, and displays a high level of functional group compatibility.
- Berk, Scott C.,Buchwald, Stephen L.
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p. 3751 - 3753
(2007/10/02)
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- Asymmetric hydroboration of styrenes catalyzed by cationic chiral phosphine-rhodium(I) complexes
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Reaction of styrene with catecholborane in the presence of 1 mol % of a cationic phosphine-rhodium catalyst prepared in situ from [Rh(COD)2]BF4 and 1,4-bis(diphenylphosphino)butane proceeded regioselectively to give, after oxidation, 1-phenylethanol in a quantitative yield. The regioselectivity forming benzylic alcohols was also observed in the reaction of substituted styrenes. Use of (R)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) as a chiral ligand for the rhodium-catalyzed hydroboration of substituted styrenes (ArCH=CH2) gave optically active (R)-1-arylethanols (ArCH(OH)Me) in high yields. The enantiomeric purities of the alcohols are 96% ee, 94% ee, 91% ee, 85% ee, 89% ee, and 82% ee for Ar=Ph, 4-MeC6H4, 4-ClC6H4, 3-ClC6H4, 4-MeOC6H4, and 2-MeOC6H4, respectively.
- Hayashi,Matsumoto,Ito
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p. 601 - 612
(2007/10/02)
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- The Catalytic Reduction of Aldehydes and Ketones with 2-Propanol over Hydrous Zirconium Oxide
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Reduction of aldehydes with 2-propanol proceeded efficiently by catalysis with hydrous zirconium oxide to give the corresponding alcohols.Most ketones also were reduced efficiently, but conjugated or sterically hindered ketones resisted the reduction.The reduction was carried out with primary, secondary, or tertiary alcohols, and only secondary alcohols served as hydrogen donors.Kinetic experiments have indicated that the reaction rate is first-order dependence on each of the concentrations of the carbonyl compound, 2-propanol, and the catalyst.An observation of the primary isotope effect has suggested that a step of hydride transfer from absorbed 2-propanol to absorbed carbonyl compound constitutes the rate-determining step for the reduction.
- Shibagaki, Makoto,Takahashi, Kyoko,Matasushita, Hajime
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p. 3283 - 3288
(2007/10/02)
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- The Autoxidation of 1-Phenylalk-1-ynes. Proof of Oxirenes as Intermediates in the Oxidation of Acetylenes
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In the autoxidations of 1-phenylprop-1-yne, 1-phenylbut-1-yne, and 1-phenyl-3-methylbut-1-yne a considerable attack at the CC triple bond takes place.Both products of the oxidative cleavage of the CC bond and products formed through the corresponding oxirenes were detected.The oxirenes rearrange via the isomeric ketocarbenes to ketenes, which yield the corresponding carboxylic acids or their esters.A part of the intermediate ketenes is oxidized with decarboxylation to lower ketones.All products were identified and quantitatively determined after LiAlH4 reduction to the corresponding alcohols.
- Dao, Le Thi Anh,Blau, Karla,Pritzkow, Wilhelm,Schmidt-Renner, Wolfgang,Voerckel, Volkmar,Willecke, Lothar
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- Photochemistry of 3-Alkylated and 3-Phenylated Oxepin-2(3H)-one Derivatives
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The direct and triplet-sensitized photochemistry of the 3,3-dimethyl- (1), 3-isopropyl- (9), 3-methyl-3-phenyl- (15a), and 3-phenyl- (15b) oxepin-2(3H)-one derivatives has been studied.All derivatives underwent, upon direct irradiation, competitively decarbonylation and cyclisation to give the conjugated dienal derivatives (7), (8), (11), (16), (17), and (36) and the 2-oxabicyclohept-6-en-3-one derivatives (2), (12), (13), (18), and (19).The triplet-sensitization of the 3-alkylated oxepinones (1) and (9) by methyl 2-naphthyl ketone gave rise exclusively to the cyclisation products (2), (12), and (13).In the case of (9), it was shown that heating a solution of (9) at 82 deg C produced and equilibrating mixture (ca. 3.6 : 1) of (9) and the fully conjugated 2(7H)-isomer (10), and irradiation at this temperature with >300 nm light led selectively to the isomeric cyclobuteno-lactone derivative (14), the cyclisation product of (10).In contrast, it was found that the triplet-sensitized photolysis of the 3-phenylated oxepinones (15) in neutral media proceeded through a completely different reaction pathway, phenyl-shifting rearrangements, giving rise to the 7-phenyl-2-oxabicyclohept-4-en-3-one derivatives (20) and (21) as together the major product, 5-phenyloxepin-2(5H)-one derivatives (22), 4-methyl-1-phenyl-2-oxabicyclohept-6-en-3-one (23), and 2-phenyl-3-oxabicyclohept-6-en-4-one (37).No photocyclisation of (15) could be detected.When the sensitized photoreaction of (15) was conducted in acidic methylene dichloride, only the 5-styrylfuran-2(5H)-one derivatives (44) and (45) were obtained.Any of the photoproducts from the reaction in neutral media could not be detected.Products were identified on the basis of spectral data and chemical transformations or alternative syntheses.From the results, the 1,5-phenyl shifted compounds, the 7-phenyloxepin-2(7H)-one derivatives (40), have been proposed as the initial sensitized photoproducts of (15) and proved definitely by the synthesis and reactions of (40), and finally by the actual isolation of (40a) from the photoreaction of (15a) in acetone at -78 deg C.Thus, it has been clarified that, from (40), the di-?-methane rearrangement leads to (20) and (21), the photocyclisation leads to (37), the thermal 1,5-hydrogen shift and the subsequent photocyclisation leads to (23), and the acid-promoted translactonisation leads to (45), and that the products (22) arise from (20) and/or (21) by reverse di-?-methane rearrangement.
- Hoshi, Nobuto,Sato, Kazuhiro,Uda, Hisashi,Hagiwara, Hisahiro
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p. 3501 - 3596
(2007/10/02)
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- THE ATE COMPLEXES OF ALUMINIUM. REACTIVITY AND STEREOSELECTIVITY WITH RESPECT TO EPOXIDES AND CARBONYL COMPOUNDS. CATALYTIC ACTIVATION BY SALTS OF TRANSITION METALS
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When used in non-coordinating solvents (hydrocarbons) NaAlEt4 and LiAlnBu4 are good alkylation agents for epoxides.The presence of catalytic quantities of transition-metal salts, particularly NiCl2 or NiBr2, greatly accelerate the reactions, making them possible within a reasonable time in the case of disubstituted epoxides such as cyclohexene oxide, 2-3 epoxybutane, 1 phenyl-2,3-epoxybutane.In the case of aliphatic epoxides, dialkylmagnesium, NaAlEt4 and LiAlnBu4 lead mainly to alkylation of the least substituted carbon of the epoxide ring; while in the case of epoxides with C-O bond in the benzyl position, it is this carbon that is alkylated.The reaction always proceeds by total inversion of the configuration of the carbon in the epoxide ring, namely the site of the alkylation. NaAlEt4 is also good agent for alkylating carbonyl compounds when used in solvents of low basicity such as diethylether, or in totally non-coordinating solvents such as the hydrocarbons.The yields of the alcohol are greatly improved by using catalytic quantities of NiCl2.The behaviour of NaAlEt4 with 2-phenylpropanol is quite remarkable: in diethylether NaAl-Et4 gives predominantly the pair of enantiomers predicted by Cram's rule and with greater stereoselectivity than if EtMgBr was used, while in pentane the reaction is no longer stereoselective.Finally, with a cyclic ketone, 4-t-butylcyclohexanone, NaAlEt4 in diethylether and in hexane in the presence of NiCl2 gives predominantly the equatorial alcohol resulting from an axial attack, which is generally not favoured at all.
- Boireau, G.,Abenhaim, D.,Henry-Basch, E.
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p. 3061 - 3070
(2007/10/02)
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