- Palladium-catalyzed isomerization of methylenecyclopropanes in acetic acid
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PD(PPh3)4-catalyzed isomerization of MCPs 1 in acetic acid proceeds smoothly at 80 °C in toluene to give the corresponding I-substituted or 1,1-disubstituted dienes 2 in good to excellent yields under mild conditions. The plausible mechanism has been disclosed on the basis of a deuterium-labeling experiment.
- Shi, Min,Wang, Bao-Yu,Huang, Jin-Wen
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- Potassium tris(triflyl)methide (KCTf3): A broadly applicable promoter for cationic metal catalysis
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KCTf3, a commercially available, easily handled neutral salt, enhanced the reaction rates and the chemical yields of a wide spectrum of cationic metal catalyzed reactions, ranging from traditional Lewis acid catalysis to transition metal catalysis.
- Han, Junbin,Lu, Zhichao,Wang, Weibo,Hammond, Gerald B.,Xu, Bo
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p. 13740 - 13743
(2015/09/07)
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- Palladium-catalyzed oxidative arylhalogenation of alkenes: Synthetic scope and mechanistic insights
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This article describes the development of a Pd-catalyzed reaction for the arylhalogenation (halogen = Cl or Br) of diverse α-olefins by oxidatively intercepting Mizoroki-Heck intermediates. These transformations afford synthetically useful 1,2- and 1,1-arylhalogenated products in good yields with good to excellent selectivities that can be modulated by changing the nature of the halogenating reagent and/or the reaction conditions. The selectivity of these reactions can be rationally tuned by (i) controlling the relative rates of oxidative functionalization versus β-hydride elimination from equilibrating PdII-alkyl species and (ii) stabilization of organometallic PdII intermediates through the formation of π-benzyl adducts. These arylhalogenations exhibit modest to excellent levels of stereoselectivity, and the key carbon-halogen bond-forming step proceeds with predominant retention of stereochemistry at carbon.
- Kalyani, Dipannita,Satterfield, Andrew D.,Sanford, Melanie S.
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supporting information; experimental part
p. 8419 - 8427
(2010/08/04)
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- Lewis acid-catalyzed ring-opening reactions of methylenecyclopropanes with alcoholic or acidic nucleophiles
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(matrix presented) Nu-H can be alcohols, thiols, phenols, carboxylic acids yield: 60%-100%. Methylenecyclopropanes can react with various nucleophiles such as alcohols, phenols, carboxylic acids, and thiols to give the corresponding homoallylic esters or
- Shi, Min,Xu, Bo
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p. 2145 - 2148
(2007/10/03)
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- Asymmetric Synthesis. Asymmetric Catalytic Allylation Using Palladium Chiral Phosphine Complexes
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The general characteristics of asymmetric catalytic allylation are analyzed in terms of the properties of the allyl acetate substrates and of the putative (?-allyl)palladium(II) intermediates.After examining the diastereometric equilibria of a series of + complexes, it was established that anti-disposed ?-allyl substituents are the major source of discrimination and that aryl substituents cause an enhancement of the epimerization rate and also are responsible for the greatest discrimination.The ?-allyl substituents appear to contribute additively to the discrimination, and a sector rule is proposed for predicting diastereomeric equilibrium constants.Under appropriate conditions, it is proposed that the optical yields of asymmetric catalytic allylation can be predicted from the chiral discrimination found for these ?-allyl intermediates.These proposals were tested and optical yields of up to 86percent are reported.Quantitative chemical yields were obtained, catalysis can be performed at 25 degC, and the products are readily transformed into useful chirons.The optical yields are sensitive to the chiral phosphine used but are insensitive to the nature of the nucleophiles that were used.There is an approximate correlation of the optical yield with the previously observed diastereomeric ratio of the corresponding (?-allyl)palladium intermediate.All of the reactions are completely regioselective, and all of the nucleophiles used gave the same prevailing enantiomer of the product for a given chiral phosphine.
- Auburn, Pamela R.,Mackenzie, Peter B.,Bosnich, B.
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p. 2033 - 2046
(2007/10/02)
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- Acylation of Alcohols by Fatty Acid Esters in Presence of Lithium Aluminium Hydride
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A novel acylation of alcohols by fatty acid esters in the presence of lithium aluminium hydride is reported.A plausible mechanism of this acylation through the formation of a lithium aluminium tetraalkoxide complex has been suggested.
- Kumar, Shiv,Kansal, V. K.,Prashad, Mahavir,Bhaduri, A. P.
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p. 856 - 858
(2007/10/02)
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