- Reactions of partially solvated Grignard reagents with a ketone
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Ratios of the yields of addition and reduction products for the reactions of n-butylmagnesium chloride and bromide with diisopropyl ketone in toluene were determined at different THF, diethyl ether and methyl tertbutyl ether (MTBE) contents in the Grignard reagent. The reduction reaction yield is a maximum at the molar ratio 0.1 of THF or diethyl ether to the Grignard reagent. The addition reaction has a maximum in the region of 0.3-0.4 for the same ethers and about 1.5 for MTBE. The ratio Add/Red for conventional Grignard reagents is lower than that for partially solvated reagents. The results were discussed in terms of the solvation of the species in the reaction mixture. The decisive role of the steric requirements of the reagents over their intrinsic acid-base properties was demonstrated. Partially solvated Grignard reagents can serve as tools for the investigation of solvent effects in the Grignard reaction.
- Tuulmets, Ants,Sassian, Meeri
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- Solvation effects in the Grignard reaction with carbonyl compounds
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Ratios of the yields of addition and reduction products for the reactions of butylmagnesium chloride with diisopropyl ketone, methyl 2-methylpropanoate, and isopropyl 2-methylpropanoate in toluene were determined at different THF, diethyl ether, and tert-
- Sassian, Meeri,Tuulmets, Ants
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- Instantaneous SmI2/H2O/amine-mediated reductions in THF
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The SmI2-mediated reductions of ketones, imines, and α,β-unsaturated esters have been shown to be instantaneous in the presence of H2O and an amine in THF. The SmI2-mediated reductions are not only shown to be fast and quantitative by the addition of H2O and an amine, but the workup procedures are also simplified. Competing experiments with SmI2/H2O/amine confirmed that α,β-unsaturated esters could be selectively reduced in the presence of ketones or imines. Comparison of analogue ligands showed that nitrogen and phosphorus ligands are superior to oxygen and sulfur ligands in these reductions. The trialkylphosphine 1,2-bis(dimethylphosphino)ethane (DMPE) provided a primary kinetic isotope effect, yielding a kH/kD of 4.5.
- Dahlen, Anders,Hilmersson, Goeran
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p. 1123 - 1128
(2007/10/03)
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- Instantaneous SmI2-H2O-mediated reduction of dialkyl ketones induced by amines in THF
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Reduction of various ketones to their corresponding alcohols is shown to be instantaneous, i.e. completed in less than 10 s, by samarium diiodide (2.5 equiv.) in the presence of water (6.25 equiv.) and an amine (5 equiv.) in THF. The rates of reduction of ketones in this mixture exceed by far the rates determined by an amine or water alone. Rate enhancement is at least 100 000 compared to the reduction without a proton source, or at least 100 times faster than the rate of the widely used HMPA/alcohol accelerated reductions. This new method is therefore suggested to be an excellent replacement of the toxic HMPA/alcohol method.
- Dahlén, Anders,Hilmersson, G?ran
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p. 7197 - 7200
(2007/10/03)
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- Enantioselective butylation of aliphatic aldehydes by mixed chiral lithium amide/n-BuLi dimers
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The enantioselective butylation of aliphatic aldehydes with mixtures of n-butyllithium and chiral lithium amides in a diethyl ether-dimethoxymethane solvent mixture is described. Enantiomeric excesses ranging from 91 to 98.5% were observed for several aliphatic alcohols. The asymmetric butylation of the prochiral aldehydes proceeds much faster by the mixed lithium amide/n- BuLi complexes than by tetrameric n-BuLi.
- Arvidsson, Per I.,Davidsson, Oejvind,Hilmersson, Goeran
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p. 527 - 534
(2007/10/03)
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- Direct transformation of dialkyl sulfates into alkyllithium reagents by a naphthalene-catalysed lithiation
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The lithiation of primary and secondary dialkyl sufates with an excess of lithium powder in the presence of a catalytic amount of naphthalene (4 mol %) in THF at -78°C leads to the corresponding alkyllithium reagents (1:2 molar ratio) which react with different electrophiles, mainly carbonyl compounds, to yield after hydrolysis, the expected coupling products. This methodology represents an indirect way to transform alcohols into organolithium compounds through the corresponding dialkyl sulfates. When the same procedure is applied to five or six member cyclic sulfates (derived from 1,2- or 1,3-diols) only products arising from a β- or γ-elimination process (giving olefins or cyclopropanes), respectively, are obtained.
- Guijarro, David,Guillena, Gabricia,Mancheno, Balbino,Yus, Miguel
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p. 3427 - 3436
(2007/10/02)
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- Naphthalene-catalysed lithiation of dialkyl sulfates: A new route for organolithium reagents
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The lithiation of primary and secondary dialkyl sulfates with an excess of lithium powder in the presence of a catalytic amount of naphthalene at -78°C leads to the corresponding alkyl-lithium reagents (1:2 molar ratio), which react with different electrophiles, mainly carbonyl compounds, to yield the expected coupling products. This methodology represents an indirect way for transforming alcohols into organolithium compounds through the corresponding dialkyl sulfates.
- Guijarro,Mancheno,Yus
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p. 5597 - 5600
(2007/10/02)
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- Synthesis of α-Hydroxy Ketones by Direct, Low-Temperature, in Situ Nucleophilic Acylation of Aldehydes and Ketones by Acyllithium Reagents
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The reaction of n-, sec-, and tert-butyllithium with CO at atmospheric pressure at -110 and -135 deg C in the appropriate solvent system in the presence of ketones and aldehydes generates the acyllithium, RC(O)Li, which reacts with the carbonyl compound to give the α-hydroxy ketone, generally in good yield.Reactions with aldehydes are limited in scope, working well with the t-BuLi-derived acyllithium reagents, but not with n-BuC(O)Li.
- Seyferth, Dietmar,Weinstein, Robert M.,Hui, Richard C.,Wang, Wei-Liang,Archer, Colin M.
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p. 5620 - 5629
(2007/10/02)
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- Chiral Organometallic Reagents, IV Stereoselective Formation of β-Silyloxy-α-bromoalkyllithium Compounds
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The diastereomeric carbenoids 4 have been generated by diastereoselective (84:16) exchange of the diastereotopic bromine atoms in the dibromo compound 3 for lithium at -120 deg C.The implication of the observed diastereoselectivity for the Nozaki ring-expansion method is discussedKey words: Carbenoids / Halogen-metal exchange / Diastereotopic groups
- Hoffmann, Reinhard W.,Julius, Manfred
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p. 811 - 822
(2007/10/02)
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- HIGH YIELD ACYL ANION TRANSFER REACTIONS: NUCLEOPHILIC ACYLATION OF ALDEHYDES
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Aldehydes be may acylated to give R'CH(OH)C(O)R in good yield by the RLi/CO in situ procedure at very low temperatures.Examples are given of ketone acylations which demonstrate the advantages of 1:1 RLi/substrate stoichiometry and the use of lower (-135 deg C) temperature.
- Seyferth, Dietmar,Weinstein, Robert M.,Wang, Wei-Liang,Hui, Richard C.
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p. 4907 - 4910
(2007/10/02)
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