- Further studies on 1,5-Bu3Sn group transfer reactions. 1,5-Bu3Sn group and 1,5-hydrogen atom transfer competition
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1,5-Bu3Sn group transfer is favored over 1,5-hydrogen atom transfer roughly in a ratio of 20:1, 1,5-Bu3Sn transfers from carbon to carbon and from enoxy oxygen to carbon are observed for the first time.
- Kim, Sunggak,Lim, Kwang Min
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Read Online
- Asymmetric hydrovinylation of 1-vinylcycloalkenes. Reagent control of regio- and stereoselectivity
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1-Vinylcycloalkenes undergo highly regio- and enantioselective (>98% ee) 1,4-hydrovinylation (HV) when treated with ethylene (1 atm) at room temperature in the presence of [(S,S)-2,4-bis-diphenylphosphinopentane (BDPP)]CoCl 2 (0.05 equiv) and methylaluminoxane. The minor 1,2-HV products, seen only in 1-vinylcyclohexene (~15%) and 1-vinylcycloheptene (2%), are formed as racemic mixtures. The corresponding Ni(II)-catalyzed HV reactions of these substrates give mostly the 1,2-adducts. Racemic 4-tert-butyl-1-vinylcyclohexene, when treated with Co[(S,S)-(BDPP)]Cl2 and ethylene, undergoes a rare enantiodivergent reaction giving two diastereomers each in >98% ee.
- Page, Jordan P.,Rajanbabu
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p. 6556 - 6559
(2012/06/15)
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- MACROCYCLIC PYRIMIDINE DERIVATIVES
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Macrocyclic pyrimidine compounds, compositions comprising such compounds, methods for making the compounds, and methods of treating and preventing the progression of diseases, conditions, and disorders using such compounds and compositions are described h
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Page/Page column 84
(2009/10/17)
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- Enantioselective synthesis of α-substituted ketones by asymmetric addition of chiral zinc enamides to 1-alkenes
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A zinc enamide of a chiral imine derived from a ketone and (S)-valinol or (S)-t-leucinol undergoes addition to 1-alkene to generate a γ-zincioimine intermediate, which reacts with a carbon electrophile to give upon hydrolysis an optically active α-substituted ketone in good yield. The stereoselectivity of the addition reaction may reach 99% for the reaction of a cyclohexanone imine with ethylene. Copyright
- Nakamura, Masaharu,Hatakeyama, Takuji,Hara, Kenji,Nakamura, Eiichi
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p. 6362 - 6363
(2007/10/03)
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- Cu-catalyzed enantioselective conjugate addition of alkylzincs to cyclic nitroalkenes: Catalytic asymmetric synthesis of cyclic α-substituted ketones
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An efficient and highly enantioselective (≥92% ee) catalytic method for conjugate addition of alkylzinc reagents to cyclic nitroalkenes is reported. Reactions are promoted in the presence of 0.5-5 mol % (CuOTf)2·C6H6 and 1
- Luchaco-Cullis, Courtney A.,Hoveyda, Amir H.
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p. 8192 - 8193
(2007/10/03)
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- 1,4-Addition of diorganozincs to α,β-unsaturated ketones catalyzed by a copper(I)-sulfonamide combined system
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A mixture of CuCN and N-benzylbenzenesulfonamide catalyzes the 1,4- addition of dialkylzincs or diarylzincs (Cu: Zn = 1: 200 to 1: 10000) to α,β-unsaturated ketones to give, after aqueous workup, the corresponding β-substituted ketones in nearly quantitative yields. A range of cyclic enones having s-cis or s-trans geometries as well as conformationally flexible acyclic enones are usable as substrates. The ethyl group migrates more readily than the methyl and phenyl groups. CuOTf, CuO-t-C4H9, and mesitylcopper can be used in place of CuCN. The in situ-formed alkylzinc enolate, prior to aqueous workup, further undergoes an aldol reaction with aldehydes or Pd(0)-assisted coupling with allyl acetate, resulting in regio- controlled, vicinal carbacondensation products. A catalytic cycle is proposed on the basis of a kinetic study and a structural analysis of the zinc enolate product by NMR and molecular weight measurements.
- Kitamura, Masato,Miki, Takashi,Nakano, Keiji,Noyori, Ryoji
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p. 999 - 1014
(2007/10/03)
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- Synthesis of medium ring ethers. 5. The synthesis of (±)-laurencin
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The enantioselective synthesis of (+)-laurencin 1 has been achieved in 27 steps from (R)-malic acid 20. The key steps involved methylenation of the lactone 49 followed by intramolecular hydrosilation of the enol ether 14 (Scheme 11) and one carbon homologation of the diol 13 to give the key ethyl substituted cyclic ether 59 (Scheme 13). The lactone 49 was obtained by two efficient routes, namely a Claisen ring expansion (Scheme 3) followed by cl-hydroxylation (Scheme 6) and a Yamaguchi lactonization (Scheme 11). Elaboration of the (E)-pentenynyl side chain (Scheme 18) and introduction of bromine (Scheme 19) completed the synthesis of (+)-laurencin 1.
- Burton, Jonathan W.,Clark, J. Stephen,Derrer, Sam,Stork, Thomas C.,Bendall, Justin G.,Holmes, Andrew B.
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p. 7483 - 7498
(2007/10/03)
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- Ring enlargement of α-ethylidenecycloalkanones to β-alkylidenecycloalkanones induced by trimethylstannyllithium/aldehyde equivalents/Lewis acids
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α-Ethylidenecycloalkanones underwent a ring enlargement to β-alkylidenecycloalkanones upon a treatment with trimethylstannyllithium/aldehyde equivalents/Lewis acids with high stereoselectivity.
- Fujiwara,Tokuyasu,Sato
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p. 289 - 296
(2007/10/02)
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- A STRATEGY FOR THE ASYMMETRIC SYNTHESIS OF MEDIUM RING OXYGEN HETEROCYCLES: ENANTIOSELECTIVE TOTAL SYNTHESIS OF (+)-OCTAHYDRODEACETYLDEBROMOLAURENCIN
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The asymmetric synthesis of the laurencin degradation product (2) by methylenation of the chiral heptanolide (5), conformationally controlled hydroboration of the enol ether (6), to give exclusively the cis-alcohol (7), and introduction of the pentyl side chain, demonstrates a new approach to the enantioselective synthesis of 2,8-disubstituted oxocanes, and confirms the absolute configuration of laurencin (1).
- Clark, J. Stephen,Holmes, Andrew B.
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p. 4333 - 4336
(2007/10/02)
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