- Reduction of Organic Compounds at Lead Cathodes and Mediation by Dimethylpyrrolidinium Ion
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Reduction of several organic compounds at Pb cathodes was studied and the use of dimethylpyrrolidinium (DMP+) as a mediator for such reactions was evaluated.Following previous reports that have shown that the reduction product of DMP+ at Pb deposits as a monolayer and bulk DMP(Pb5), the catalytic properties of both phases for organic electroreduction were investigated.Of the organic compounds investigated, the monolayer catalyzes the reduction of alkyl chlorides only.Bulk DMP(Pb5) mediates electron transfer also to several ketones, allylbenzene, and difluorobenzene.Of particular interest is the fact that the reduction of 6-hepten-2-one (5), 6-heptyn-2-one, and 5-phenylpentan-2-one can be catalyzed whereas other ketones are unaffected.Preparative electrolyses at Pb were performed with 6-chloro-1-hexene (4) and 6-hepten-2-one (5).The main product of 4 was 1-hexene, whereas 5 yielded 1,2-dimethylcyclopentanol exclusively.The reduction of 4 and 5 in the presence of catalytic amounts of DMP+ can be achieved at potentials 400 - 500 mV positive of the reduction potentials when DMP+ is absent.The mechanism of the reductive cyclization of 5 is discussed.
- Lawin, Phillip B.,Hutson, Alan C.,Kariv-Miller, Essie
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- Efficient and selective oxidation of methyl substituted cycloalkanes by heterogeneous methyltrioxorhenium-hydrogen peroxide systems
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Polymer-supported methyltrioxorhenium (MTO) systems are efficient catalysts for the oxidative functionalisation of cyclohexane and cyclopentane derivatives with H2O2 as oxygen donor. Using poly(4-vinyl)pyridine and poly(4-vinyl)pyridine-N-oxide as MTO supports, cycloalkanol, cycloalkanediol, cycloalkanone and ω-hydroxy methyl ketone derivatives were obtained in different yields depending on the experimental conditions. Interestingly, cycloalkane dimers were selectively recovered in acceptable to good yields when the oxidation was performed with polystyrene-microencapsulated MTO catalyst. The EPR investigation suggests that the homolytic cleavage of the CH3-Re bond with formation of CH3{radical dot} radicals occurs inside the polystyrene capsule, indicating a possible role of methyl radical in the cycloalkane dimerisation pathway.
- Bianchini, Gianluca,Crucianelli, Marcello,Canevali, Carmen,Crestini, Claudia,Morazzoni, Franca,Saladino, Raffaele
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p. 12326 - 12333
(2007/10/03)
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- Reductive cyclization of enones by titanium(IV) aryloxide and a Grignard reagent
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The titanium-mediated cyclization of δ,ε-enones by using dichlorotitanium diphenoxide-cyclohexylmagnesium chloride diastereoselectively afforded cis-substituted cyclopentanols and was thus found to parallel the stoichiometric and catalytic titanocene-mediated reactions.
- Quan, Long Guo,Cha, Jin Kun
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p. 8567 - 8569
(2007/10/03)
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- Regio- and stereoselective intramolecular cyclization of some unconjugated ketones at mercury pool cathode
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This work describes preparative scale electroreductive regio- and stereoselective intramolecular cyclization of some unconjugated ketones at mercury pool cathode in dimethylformamide-2-propanol using tetrabutylammonium fluoroborate as supporting electrolyte and (-)-N,N'-dimethylquininium tetrafluoroborate as a stereo controlled cyclizing agent to yield cis-cyclized products in good yield. Cyclic voltammetric studies have been carried out and a probable mechanism of the process has been presented.
- Yadav,Singh
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p. 1199 - 1201
(2007/10/03)
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- Development of a method for the reductive cyclization of enones by a titanium catalyst
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An effective protocol in which bis(trimethylphosphine)titanocene is used to catalyze the reductive cyclization of enones to cyclopentanols via a metallacyclic intermediate has been developed. The key step in the process is the cleavage of the titanium-oxygen bond in the metallacycle by a silane to regenerate the catalyst. Mechanistic aspects of the reaction are discussed and the diastereoselectivity of the transformation is studied using both achiral and chiral substrates. The scope and limitations of the procedure are described. An in situ protocol for the generation of the air- and moisture-sensitive catalyst has also been developed. This work demonstrates, for the first time, the viability of using an early transition metal complex to catalyze the reductive cyclization of an alkene with a heteroatom-containing functional group.An effective protocol in which bis(trimethylphosphine) titanocene is used to catalyze the reductive cyclization of enones to cyclopentanols via a metallacyclic intermediate has been developed. The key step in the process is the cleavage of the titanium-oxygen bond in the metallacycle by a silane to regenerate the catalyst. Mechanistic aspects of the reaction are discussed and the diastereoselectivity of the transformation is studied using both achiral and chiral substrates. The scope and limitations of the procedure are described. An in situ protocol for the generation of the air-and moisture-sensitive catalyst has also been developed. This work demonstrates, for the first time, the viability of using an early transition metal complex to catalyze the reductive cyclization of an alkene with a heteroatom containing functional group.
- Kablaoui, Natasha M.,Buchwald, Stephen L.
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p. 3182 - 3191
(2007/10/03)
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- Stereochemical Investigations of Samarium(II) Iodide-Promoted 5-Exo and 6-Exo Ketyl-Olefin Radical Cyclization Reactions
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Samarium(II) iodide (SmI2)-promoted ketyl cyclizations of several substituted, unsaturated ketones, providing various cyclpentyl and cyclohexyl systems, have been investigated.The resulting experiments provide stereochemical insight into these reactions and in addition outline the synthetic potential of these 5-exo and 6-exo radical cyclization processes.
- Molander, Gary A.,McKie, Jeffrey A.
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p. 872 - 882
(2007/10/02)
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- Electroorganic Chemistry. 144. Electroreductive Coupling of Ketones with O-Methyl Oximes, N,N-Dimethylhydrazones, amd Nitrones. A Convenient Route to Synthesis of β-Amino Alcohol
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The intermolecular coupling of a variety of ketones with some types of O-methyl oximes took place when a mixture of both components was electrochemically reduced in i-PrOH with an Sn cathode.The product, β-methoxyamino alcohol was easily converted to β-amino alcohol by simple reduction.A chiral ligand effective for the enantioselective addition of diethylzinc to an aldehyde was easily obtained from the product formed by the electroreductive coupling of (-)-menthone with O-methylacetaldoxime.The intermolecular coupling of a ketone with a N,N-dimethylhydrazone or nitrone was also promoted by the electroreduction.Furthermore, the electroreductive coupling of a carbonyl group with an intramolecular O-methyl oxime moiety gave the corresponding cyclized product stereoselectively.
- Shono, Tatsuya,Kise, Naoki,Fujimoto, Taku,Yamanami, Ayuko,Nomura, Ryoji
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p. 1730 - 1740
(2007/10/02)
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- Samarium(II) Iodide-Induced Reductive Cyclization of Unactivated Olefinic Ketones. Sequential Radical Cyclization/Intermolecular Nucleophilic Addition and Substitution Reactions
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Samarium(II) iodide in the presence of HMPA effectively promotes the intramolecular coupling of unactivated olefinic ketones by a reductive ketyl-olefin radical-cyclization process.The reaction is quite general for the formation of 5- and 6-membered carbocycles and even provides modest yields in less facile cyclization processes as evidenced by the generation of methylcyclooctanol via an 8-endo cyclization.Sequential radical cyclization-intermolecular nucleophilic addition/substitution processes set the SmI2 reaction apart from its radical-chain, photochemical, and electrochemical counterparts.In addition to delineating the synthetic potential of this reaction, the role played by HMPA in enhancing SmI2 reactivity has been further refined, and a model correlating the high diastereoselectivity and product distribution in SmI2-promoted reductive coupling processes with HMPA concentration has been established.
- Molander, Gary A.,McKie, Jeffrey A.
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p. 3132 - 3139
(2007/10/02)
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- Homogeneous Redox Catalysis Study of the Reductive Cyclization of 6-Hepten-2-one. Unusual Effects of the Nature and Concentration of the Catalyst
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Electrochemical reductive cyclization of 6-hepten-2-one can be effected by homogeneous redox catalysts.Effective catalysts include biphenyl, 2-methoxybiphenyl, naphthalene, and phenanthrene.The reaction consumed 2 F mol1-, and cis- and trans-1,2-dimethylcyclopentanol were formed as exclusive products.The percentage of the cyclic alcohol that was cis increased with increasing redox catalyst concentration, increasingly positive reduction potentials of the catalyst, and increasing amounts of water present in the medium.These results are explained by invoking amechanism involving reversible cyclization of the ketyl radical anion formed from reduction of 6-hepten-2-one.The cis or trans cyclized radical anions can be trapped by further reduction or by protonation to (ultimately) form the observed products.
- Swartz, James E.,Kariv-Miller, Essie,Harrold, Steven J.
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p. 1211 - 1216
(2007/10/02)
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- Selective Cyclization and Pinacolization Directed by Tetraalkylammonium Ions
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The effect of the electrolyte composition on the cathodic reduction of cyclohexanone and 6-hepten-2-one was investigated.It was found that addition of catalytic amounts of certain tetraalkylammonium salts to the electrolysis solution alters the reaction pathways.Using a mercury cathode in DMF, dimethylpyrrolidinium (DMP+) tetrafluoroborate, shifts the potential required for preparative reduction to less negative values and changes the reaction products.Cyclohexanone yields the corresponding pinacol and 6-hepten-2-one is stereoselectively cyclized to cis-1,2-dimethylcyclopentanol (95percent).In the absence of DMP+ both substrates are reduced to the corresponding simple alcohols.Stereoselective reductive cylization in DMF can also be induced by tetraethylammonium cations (TEA+) on mercury and by either DMP+ or TEA+ on graphite electrodes.The combination of DMR+ and mercury results in excellent chemical yield and current efficiency.On the basis of results of preparative electrolyses under various conditions and cyclic voltammograms, a mechanism involving the initial reduction of the catalyst cation with participation of the electrode material is proposed.It is suggested that catalysis by specific tetraalkylammonium ions can lead to a preference for one-electron reaction routes.
- Kariv-Miller, Essie,Mahachi, Tendai J.
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p. 1041 - 1045
(2007/10/02)
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