- Asymmetric transfer hydrogenation of unsaturated ketones; factors influencing 1,4- vs 1,2- regio- and enantioselectivity, and alkene vs alkyne directing effects
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A detailed study has been completed on the asymmetric transfer hydrogenation (ATH) of a series of enones using Ru(II) catalysts. Electron-rich rings adjacent to the C[dbnd]O group reduce the level of C[dbnd]O reduction compared to C[dbnd]C. The ATH reaction can readily discriminate between double and triple bonds adjacent to ketones, reducing the double bond but leaving a triple bond intact in the major product.
- Hall, Thomas H.,Adams, Hannah,Vyas, Vijyesh K.,Michael Chu,Wills, Martin
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- Metal-Free tert -Butyl Hydrogenperoxide (TBHP) Mediated Radical Alkylation of Enol Acetates with Alcohols: A New Route to β-Hydroxy Ketones
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A metal-free TBHP-mediated radical alkylation of enol acetates with alcohols is described. This method provides a new route to a variety of β-hydroxy-ketones in moderate to good yields.
- Tang, Yucai,Fan, Yuanyuan,Zhang, Ye,Li, Xiaoqing,Xu, Xiangsheng
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p. 1860 - 1863
(2016/07/16)
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- Synthesis of silaoxazolinium salts bearing weakly coordinating anions: Structures and catalytic activities in the aldol reaction
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The synthesis and structures of silaoxazolinium salts 2 and their application to the catalytic Mukaiyama aldol reaction are described. The reaction of (N-amidomethyl)dimethylchlorosilane (1a) or (N-amidomethyl) bis(trimethylsilyl)chlorosilane (1b) with me
- Chandra Sheker Reddy, Anugu,Chen, Zhang,Hatanaka, Tohru,Minami, Tatsuya,Hatanaka, Yasuo
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p. 3575 - 3582
(2013/07/26)
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- Strong counteranion effects on the catalytic activity of cationic silicon lewis acids in Mukaiyama aldol and Diels-Alder reactions
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(Graph Presented) A toluene-coordinated silyl borate, [Et 3Si(toluene)]B(C6F5)4, demonstrated catalytic activities significantly higher than those of Me3SiOTf and Me3SiNTf2 in Mu
- Hara, Kenji,Akiyama, Ryuto,Sawamura, Masaya
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p. 5621 - 5623
(2007/10/03)
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- Unusual tandem alkynylation and trans-hydrosilylation to form oxasilacyclopentenes
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(Chemical Equation Presented) An unusual tandem reaction sequence to form oxasilacyclopentenes from carbonyls and alkynylsilanes in the presence of a catalytic amount of nucleophilic initiator has been discovered. The reaction proceeds readily at room tem
- Maifeld, Sarah V.,Lee, Daesung
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p. 4995 - 4998
(2007/10/03)
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- Diastereoselective reactions at enantiomerically pure, sterically congested cyclohexanes as an entry to wailupemycins A and B: Total synthesis of (+)-wailupemycin B
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Wailupemycin A (1) and B (2) are polyketide natural products with a highly substituted cyclohexanone core. Three different routes for the syntheses of these compounds were pursued, which commenced from either (R)-(-)-carvone (ent-5) or (S)-(+)-carvone (5)
- Kirsch, Stefan F.,Bach, Thorsten
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p. 7007 - 7023
(2007/10/03)
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- A high yield procedure for the Me3SiNTf2-induced carbon-carbon bond-forming reactions of silyl nucleophiles with carbonyl compounds: The importance of addition order and solvent effects
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We demonstrate the efficiency of Me3SiNTf2 (0.3-1.0 mol%) as a strong Lewis acid catalyst for the Mukaiyama aldol and Sakurai-Hosomi allylation reactions, and that the slow addition of carbonyl compounds to a solution of acid catalys
- Ishihara,Hiraiwa,Yamamoto
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p. 1851 - 1854
(2007/10/03)
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- Aluminum bis(trifluoromethylsulfonyl)amides: New highly efficient and remarkably versatile catalysts for C-C bond formation reactions
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Superacid-derived aluminum catalysts R2AlNTf2 (2-5 mol%) are highly efficient and versatile and are suitable promoters for the allylation and pentadienylation of aldehydes, aldol reactions, aldol cross-coupling of ketones, and Michae
- Marx, Andreas,Yamamoto, Hisashi
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p. 178 - 181
(2007/10/03)
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- Highly controlled chemoselectivity of tin enolate by its hybridization state. Anionic complex of tin enolate coordinated by tetrabutylammonium bromide as halo selective reagent
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The control of reactivity and/or selectivity of organotin(IV) enolates has been studied by means of a high coordination method in which the hybridization state of tin was effectively changed. An anionic tin complex, five-coordinated tin enolate 1(h), was formed by the coordination of bromide anion from tetrabutylammonium bromide (Bu4NBr) to neutral four-coordinated tin(IV) enolates 1(e). The highly coordinated enolates which attained a marked change in chemoselectivity have higher nucleophilicity to organic halides. In addition, they showed low nucleophilicity toward carbonyl moieties by the coordination of the bromide anion, whereas carbonyl addition readily proceeds using the usual four-coordinated tin enolate. NMR studies revealed the generation of HMPA- or bromide-anion-coordinated tin enolates in equilibrium between four-coordinated enolate 1c(e) and five-coordinated enolate 1c(h), showing a considerable upfield shift δ(119Sn) and increasing values of the coupling constants 1J(119Sn-13C). In detailed NMR analyses of highly coordinated tin enolate, it was shown that the contribution of highly coordinated species 1(h) to the equilibrium between 1(e) and 1(h) became more significant as the added amount of ligands such as Bu4NBr or HMPA was increased. Considering these results, it was assumed that the bromide-anion-coordinated tin enolate was generated, which showed a unique reactivity and selectivity. The effective control of chemoselectivity in the intermolecularly competitive reaction between organic halides and carbonyl compounds was demonstrated using two types of tin enolates, four-coordinated enolate and highly coordinated anionic enolate; halide displacement reaction exclusively took place using the bromide-anion-coordinated enolate, and the usual four-coordinated enolates reacted with only carbonyl compounds.
- Yasuda, Makoto,Hayashi, Keiko,Katoh, Yasuhiro,Shibata, Ikuya,Baba, Akio
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p. 715 - 721
(2007/10/03)
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- Homogeneous catalysis. Transition metal based lewis acid catalysts
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Transition metal based Lewis acids provide catalysts for the Diels-Alder and Mukaiyama reactions. These catalysts must possess an electron deficient axophilic metal center and a labile coordination position. Unlike traditional Lewis acids, those derived from transition metals can function in the presence of water and have well defined structures. It is shown how a normally electron rich ruthenium atom can be converted to a Lewis acid by incorporation of electron withdrawing ligands and ligands with hard donor atoms. This ruthenium complex, [Ru(salen)(NO)(H2O)]+, is an efficient catalyst for the Diels-Alder reaction, but in the Mukaiyama reaction, it tends to be reduced and thereby deactivated by the silyl enol ether. It is shown that the complex [TiCp*2(H2O)2]2+ (Cp* is pentamethylcyclopentadienyl) is an efficient catalyst for the Diels-Alder reaction even when water is present. Similarly, the triflato complexes [TiCp2(CF3 SO3)2] and [ZrCp2(CF3SO3)2] (Cp is cyclopentadienyl) are efficient catalysts for both the Diels-Alder and Mukaiyama reactions. All of these catalysts are effective at very low loadings of ≈ 1 mol%. Catalysis has been shown to occur via substrate-catalyst adducts and moreover these adducts are formed rapidly and reversibly as required for efficient catalysis.
- Hollis, T. Keith,Odenkirk, William,Robinson,Whelan, John,Bosnich
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p. 5415 - 5430
(2007/10/02)
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- Chiral Organosilicon Compounds in Asymmetric Synthesis of Chiral 1,3-Diols
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Chiral 1,3-diols can be prepared in high enantiomeric purity (>99percent ee) from the reactions of the chiral silylcarbanion 2 with epoxides followed by oxidative cleavage of the carbon-silicon bond with hydrogen peroxide.The absolute configurations of so
- Chan, T. H.,Nwe, K. T.
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p. 6107 - 6111
(2007/10/02)
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- Trialkylborane as an Initiator and Terminator of Free Radical Reactions. Facile Routes to Boron Enolates via α-Carbonyl Radicals and Aldol Reaction of Boron Enolates
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A variety of trialkylborane-induced reactions were examined for the preparation of the α-carbonyl radicals: (1) addition of alkyl radical to methyl vinyl ketone, (2) reduction of α-halo ketone, and (3) intramolecular radical addition to α,β-unsaturated carbonyl moiety.Trialkylborane reacted with α-carbonyl radicals to give boron enolates.The resulting boron enolates were efficiently trapped by carbonyl compounds to give β-hydroxy ketones in good yields.
- Nozaki, Kyoko,Oshima, Koichiro,Utimoto, Kiitiro
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p. 403 - 409
(2007/10/02)
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- FACILE ROUTES TO BORON ENOLATES. Et3B-MEDIATED REFORMATSKY TYPE REACTION AND THREE COMPONENTS COUPLING REACTION OF ALKYL IODIDES, METHYL VINYL KETONE, AND CARBONYL COMPOUNDS
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Reaction of α-bromoketones with Ph3SnH in the presence of Et3B provides boron enolates which react with carbonyl compounds to give β-hydroxyketones in good yields.Et3B-induced Reformatsky type reaction of α-iodoketones with an aldehyde or ketone proceeds without Ph3SnH.
- Nozaki, Kyoko,Oshima, Koichiro,Utimoto, Kiitiro
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p. 1041 - 1044
(2007/10/02)
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- REFORMATSY TYPE REACTION BY MEANS OF Bu3SnAlEt2 or Bu3PbAlEt2
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Treatment of α-halo carbonyl compounds with title Sn-Al or Pb-Al reagents provides enolates which react with aldehydes or ketones to give β-hydroxy carbonyl compounds effectively.
- Tsuboniwa, Noriyuki,Matsubara, Seijiro,Morizawa, Yoshitomi,Oshima, Koichiro,Nozaki, Hitosi
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p. 2569 - 2572
(2007/10/02)
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- 1,4-DIANION OF ACETOPHENONE N-ETHOXYCARBONYLHYDRAZONE AS A SYNTHETIC INTERMEDIATE
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Various β-hydroxyketones and α,β-unsaturated ketones were prepared by the reaction of aldehydes and ketones with 1,4-dianion (2) which is derived from acetophenone N-ethoxycarbonylhydrazone (1) with butyllithium.In the reaction of 2 with carbonyl compounds such as ester, amide, acid anhydride, acyl chloride, and alkyl carbonate, pyrazole derivatives were obtained in good yields.
- Matsumura, Noboru,Kunugihara, Akira,Yoneda, Shigeo
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p. 3239 - 3242
(2007/10/02)
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