- Lewis Acid Assisted Electrophilic Fluorine-Catalyzed Pinacol Rearrangement of Hydrobenzoin Substrates: One-Pot Synthesis of (±)-Latifine and (±)-Cherylline
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A microwave-irradiated solvent-free pinacol rearrangement of hydrobenzoin substrates catalyzed by a combination of N-fluorobenzenesulfonimide and FeCl3·6H2O was developed. Its selectivity was first investigated by density functional theory (DFT) calculations. Then the functional group tolerance was examined by synthesizing a series of substrates designed based on the insight provided by the DFT calculations. The application of the methodology was demonstrated by the efficient one-pot synthesis of (±)-latifine and (±)-cherylline, both are 4-aryltetrahydroisoquinoline alkaloids isolated from Amaryllidacecae plants.
- Shi, Hui,Du, Chuan,Zhang, Xinhang,Xie, Fukai,Wang, Xiaoyu,Cui, Shanshan,Peng, Xiaoshi,Cheng, Maosheng,Lin, Bin,Liu, Yongxiang
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p. 1312 - 1319
(2018/02/09)
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- Enantioselective borohydride reduction of aliphatic ketones catalyzed by ketoiminatocobalt(iii) complex with 1-chlorovinyl axial ligand
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For the enantioselective borohydride reduction of aliphatic ketones, the optically active ketoiminatocobalt(II) catalysts was successfully designed based on their axial ligand. Instead of chloroform for the aryl ketone reduction, various axial ligand precursors were examined for the aliphatic ketone. Consequently, 1, 1, 1-trichloroethane was found to be the most effective activator of the cobalt(II) complexes to generate the corresponding 1-chlorovinyl cobalt(III) derivatives as the reactive intermediate. Several aliphatic ketones were successfully reduced to afford the corresponding secondary alcohols with high enantioselectivities.
- Tsubo, Tatsuyuki,Chen, Hsiu-Hui,Yokomori, Minako,Fukui, Kosuke,Kikuchi, Satoshi,Yamada, Tohru
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supporting information; scheme or table
p. 780 - 782
(2012/09/22)
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- Unexpected TiIII/Mn-promoted pinacol coupling of ketones
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Titanocene(III) chemistry has emerged in the last decades as an indispensable tool in C-C bond-forming reactions. In this context, pinacol and related reactions allow the stereoselective synthesis of vicinal diols. In this work, we present new applications of these reactions using as starting materials aromatic ketones. Simple and smooth reaction conditions have been developed and have been applied for inter- and intramolecular processes. We also describe that although Cp2TiCl is usually used as a monoelectronic reducing agent, it can be also used as an efficient Lewis acid.
- Paradas, Miguel,Campana, Araceli G.,Estevez, Rosa E.,De Cienfuegos, Luis Alvarez,Jimenez, Tania,Robles, Rafael,Cuerva, Juan M.,Oltra, J. Enrique
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experimental part
p. 3616 - 3619
(2009/09/06)
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- Electroreductive crossed pinacol coupling of aromatic ketones with aliphatic ketones and aldehydes
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The intermolecular crossed pinacol coupling of aromatic ketones with aliphatic aldehydes and ketones was effected by electroreduction in the presence of chlorotrimethylsilane. The best result was obtained using a Pb cathode in Bu4NPF6/sub
- Kise, Naoki,Shiozawa, Yousuke,Ueda, Nasuo
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p. 5415 - 5426
(2008/01/07)
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- Mg-promoted mixed pinacol coupling
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Mg-promoted reduction of a mixture of aromatic ketones (or imines) and aliphatic carbonyl compounds in N,N-dimethylformamide (DMF) brought about unique mixed pinacol type of cross coupling to give unsymmetrical vicinal diols (or amino alcohols) or α-hydroxyketones in good to moderate yields. The reaction may be initiated by electron transfer from magnesium metal to an aromatic carbonyl compound possessing a less negative reduction potential. The difference of reduction potential between aromatic ketones (or imines) and aliphatic carbonyl compounds was found to be one of the important key factors in this selective cross coupling.
- Maekawa, Hirofumi,Yamamoto, Yoshimasa,Shimada, Hisashi,Yonemura, Kazuaki,Nishiguchi, Ikuzo
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p. 3869 - 3872
(2007/10/03)
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- An improved version of the Sharpless asymmetric dihydroxylation
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The osmium catalyzed asymmetric dihydroxylation of olefins (Sharpless AD) was studied under controlled pH conditions. It was found that providing a constant pH value of 12.0 leads to improved reaction rates for internal olefins. Hydrolysis aids such as methanesulfonamide can be omitted. For terminal olefins, working at a constant pH of 10.0 at room temperature leads to higher enantioselectivities compared to AD reactions without pH control. (C) 2000 Elsevier Science Ltd.
- Mehltretter,Dobler,Sundermeier,Beller
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p. 8083 - 8087
(2007/10/03)
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- Synthesis of unsymmetrical diolate, oxametallacyclopentene, amido-alkoxide and thiolato-alkoxide complexes using dialkyl and diaryl titanium aminotroponiminate complexes: A route to unsymmetrical vicinal diols
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The reactivity of [TiR2(Me2ATI)2] complexes, where Me2ATI = N,N′-dimethylaminotroponiminate, or L, with CO or RNC in the presence of various organic electrophiles has been investigated. The compounds TiMe2L2 and TiPh2L2 react with CO and aldehydes or ketones to afford unsymmetrical diolate complexes that convert to the corresponding vicinal diols after hydrolysis. Phenyl acetylene also reacts to form the oxametallacyclopentene complex [Ti(OCMe2CH=CPh)(Me2ATI)2]. Treatment of TiMe2L2 with RNC yields the free imine and a source of low-valent titanium. Trapping this intermediate with 2 equiv of benzaldehyde or benzil affords the titanium diolate or enediolate complex, respectively. When 1 equiv each of benzophenone and either N-tosylbenzaldimine or acetone were added to the intermediate, [Ti(Ph2COCN(SO2tol)HPh)(Me2-ATI)2] and [Ti(Ph2COCOMe2)(Me2ATI)2], respectively, were obtained. The titanium thiolato-alkoxide complex [Ti(Ph2CSCOMe2)(Me2ATI)2] was prepared by use of thiobenzophenone and acetone. This chemistry allows for the preparation of unsymmetrical diols and oxametallacyclopentene complexes from Ti(IV) dialkyls, CO, and either carbonyl compounds or alkynes. Amido-alkoxide and thiolato-alkoxide complexes can be prepared by the reaction of Ti(IV) dialkyl complex, 2 equiv of benzophenone, and either an imine or thioketone.
- Steinhuebel, Dietrich P.,Lippard, Stephen J.
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p. 11762 - 11772
(2007/10/03)
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- Reactivity and Selectivity in the Oxidation of Styrene Derivatives. IV. Studies on the Oxidation of Substituted β,β-Dimethylstyrenes
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The liquid phase oxidation of substituted (p-MeO-, p-Cl-, m-CF3-) 2-aryl-3-methyl-but-2-enes, of 1,1-diphenyl-2-methyl-propene, of 1-ethoxy-2-methyl-1-phenyl-propene and of 9-isopropylidene-fluorene with pure oxygen was investigated in chlorobenzene solution and in presence of cumene and of cumene hydroperoxide in the temperature range 65-125°C. The product yields were determined gaschromatographically. The differences of the activation energies of epoxide formation and the parallel reactions were calculated. They amount to 19-48 kJ/mol. The epoxide selectivity increases with increasing temperature and increasing concentration of olefin. The relative chain propagation constants (kpC=C) were determined by competitive oxidation with cumene. The kpC=C values of substituted β,β-dimethylstyrenes can be correlated by a LFE-relationship with the ionisation energies of the olefins.
- Suprun
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p. 247 - 255
(2007/10/03)
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- Prostaglandin derivatives
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Derivatives of 11-deoxy-PGE2 are prepared. These new compounds not heretofore found in nature possess various pharmacological activities, one of which is bronchodilation.
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