- Palladium-Catalyzed Cross-Coupling of Silyl Electrophiles with Alkylzinc Halides: A Silyl-Negishi Reaction
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We report the first example of a silyl-Negishi reaction between secondary zinc organometallics and silicon electrophiles. This palladium-catalyzed process provides direct access to alkyl silanes. The delicate balance of steric and electronic parameters of the employed DrewPhos ligand is paramount to suppressing isomerization and promoting efficient and selective cross-coupling.
- Cinderella, Andrew P.,Vulovic, Bojan,Watson, Donald A.
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supporting information
p. 7741 - 7744
(2017/06/21)
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- Terminal-Selective Functionalization of Alkyl Chains by Regioconvergent Cross-Coupling
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Hydrocarbons are still the most important precursors of functionalized organic molecules, which has stirred interest in the discovery of new C?H bond functionalization methods. We describe herein a new step-economical approach that enables C?C bonds to be constructed at the terminal position of linear alkanes. First, we show that secondary alkyl bromides can undergo in situ conversion into alkyl zinc bromides and regioconvergent Negishi coupling with aryl or alkenyl triflates. The use of a suitable phosphine ligand favoring Pd migration enabled the selective formation of the linear cross-coupling product. Subsequently, mixtures of secondary alkyl bromides were prepared from linear alkanes by standard bromination, and regioconvergent cross-coupling then provided access to the corresponding linear arylation product in only two steps.
- Dupuy, Stéphanie,Zhang, Ke-Feng,Goutierre, Anne-Sophie,Baudoin, Olivier
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supporting information
p. 14793 - 14797
(2016/11/23)
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- A novel route for the synthesis of alkanes from glycerol in a two step process using a Pd/SBA-15 catalyst
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Glycerol is produced as a valuable by-product in the transesterification of fatty acids, but it cannot be used directly as a fuel additive. In this study, we developed a systematic conversion for glycerol, which proceeds via synthesizing the key intermediate, 1,2,3-tribromopropane and using the Suzuki coupling reaction to introduce the alkyl group. A series of Pd/SBA-15 catalysts with different wt% of Pd (10%, 15% and 20%) was prepared by a one step sol-gel method. The structure and composition of the catalysts were characterized by X-ray diffraction analysis (XRD), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectrometry (ICP-OES). The metallic state of dispersed palladium in SBA-15 is confirmed with X-ray photoelectron spectroscopy (XPS). Pd/SBA-15 with a Pd loading of 20 wt% shows good catalytic activity at 90 °C with methylboronic acid, allowing the complete conversion of 1,2,3-tribromopropane and 64% selectivity of 3-methylpentane. The optimized catalysts were also employed in coupling reactions between various alkylhalides and methylboronic acid, which obtained the desired product with an excellent selectivity. The catalyst can be successfully recycled five times. After the first cycle, we observed a drop in activity with 20% Pd/SBA-15, which was due to the leaching of palladium but in the later cycles, there was no significant decrease in activity.
- Udayakumar,Pandurangan
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p. 78719 - 78727
(2015/10/05)
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- Tribromoisocyanuric acid/triphenylphosphine: A new system for conversion of alcohols into alkyl bromides
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An efficient and facile method has been developed for the conversion of alcohols into alkyl bromides under neutral conditions using tribromoisocyanuric acid and triphenylphosphine (molar ratio 1.0:0.7:2.0, alcohol/ tribromoisocyanuric acid/triphenylphosphine) in dichloromethane at room temperature. This method can be applied for the conversion of primary, secondary, benzylic and allylic alcohols, and their corresponding bromides are obtained in 67-82 percent yield. Tertiary alcohols do not react under these conditions.
- De Andrade, Vitor S.C.,De Mattos, Marcio C.S.
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p. 975 - 979
(2014/06/24)
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- ORGANOBORANES FOR SYNTHESIS. 11. PREPARATION OF ALKYL BROMIDES IN THE DARK REACTION OF BROMINE WITH ORGANOBORANES. EXCEPTIONAL REACTIVITY TOWARD RADICAL BROMINATION OF THE ALPHA HYDROGEN IN TRIALKYLBORANES
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The reaction of the three isomeric tributylboranes (tri-n-butyl, triisobutyl and tri-sec-butyl) with bromine in the dark gives rise to both butyl bromide and hydrogen bromide when carbon tetrachloride is used as a solvent.The rate of disappearance of the borane and bromine are essentially equal and decreases in the order sec-butyl n-butyl isobutyl.However, the corresponding butyl bromide appears at a much slower rate and the formation of hydrogen bromide is quite rapid during the initial stages of the reaction.The amount of hydrogen bromide produced in the reaction reaches a peak in 1 h and then decreases with time.Similar results are obtained in cyclohexane.In methylene chloride, the rate of initial disappearance of bromine and tributylborane compares closely to the results obtained in carbon tetrachloride and cyclohexane.However, butyl bromide is formed with essentially the same rate as the rate of disappearance of the borane.Moreover, hydrogen bromide is formed in only minor amounts and the yields of alkyl bromides are high.In tetrahydrofuran, tri-n-butylborane and tri-sec-butylborane react at a rate similar to the rate of formation of the corresponding bromobutanes.This raction is proposed to involve a slow, direct electrophilic attack of bromine, or its complex with THF, on tributylborane.Whereas in carbon tetrachloride, cyclohexane and methylene chloride, a fast, initially free-radical bromination, followed by a slow cleavage of the resulting α-bromoorganoborane with hydrogen bromide, takes place.Evidence supporting this mechanism is given.Competitive bromination studies reveal that the α-hydrogen in trialkylboranes is highly reactive toward free-radical bromination in the dark reaction.As an important synthetic application of this new reaction, the preparation of alkyl bromides is presented.
- Brown, Herbert C.,Lane, Clinton F.,de Lue, Norman R.
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p. 2773 - 2784
(2007/10/02)
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- Crossover Products from Joint Reactions of Alkenes, Alkynes, and Hydrogen Halides
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Joint reactions of alkenes, alkynes, and hydrogen bromide or hydrogen chloride were examined.Ethylene was the only olefin which afforded a crossed cycloadduct, viz. 1-bromo-1-methylcyclobutane (3), in its reaction with propyne and HBr.Reactions of propene with propyne/HBr, with 1-butyne/HCl, and with 2-butyne/HCl as well as reactions of 1-butene with propyne/HBr gave only cyclic and/or acyclic crossover products, which are derived from alkylation of the alkyne by the alkene.Dihalotrialkylcyclobutanes were obtained as cyclic crossover products, which had carbon skeletons composed of two molecules of the acetylene and of one molecule of the olefin used.
- Griesbaum, Karl,Mach, Helmut
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p. 3818 - 3829
(2007/10/02)
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