- Determining the Scope of the Organolanthanide-Catalyzed, Sequential Intramolecular Amination/Cyclization Reaction: Formation of Substituted Quinolizidines, Indolizidines, and Pyrrolizidines
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The scope of the lanthanide-mediated, intramolecular amination/cyclization reaction was determined for the formation of substituted quinolizidines, indolizidines, and pyrrolizidines. A methyl group was installed at diverse positions in the substrates to d
- Molander, Gary A.,Pack, Shawn K.
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p. 9214 - 9220
(2007/10/03)
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- Solvolysis Rates and β-Deuterium Secondary Kinetic Isotope Effects of Some Tertiary and Secondary Alk-5-enyl Derivatives. Evidence for ?-Participation
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Tertiary 1,1-dimethylalk-5-enyl chlorides solvolyze in 80percent v/v ethanol with no or moderate rate enhancements attributable to ?-participation.However, secondary β-deuterium kinetic isotope effects (KIE, two deuterated methyl groups) are significantly reduced (kH/kD = 1.22-1.57) relative to the saturated analogues (kH/kD = 1.80), indicating participation of the double bond.Secondary 1-methylalk-5-enyl tosylates show the same trends, i.e., no or very moderate rate enhancements but reduced β-deuterium secondary KIE relative to the saturated analogue.
- Orlovic, Mirko,Borcic, Stanko,Humski, Kresimir,Kronja, Olga,Imper, Vera,et al.
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p. 1874 - 1878
(2007/10/02)
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- Concerning the Mechanism of Grignard Reagent Formation. Evidence for Radical Escape and Return to the Surface of Magnesium
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A study of the mechanism of formation of Grignard reagents using alkyl halide radical probes has been conducted.The effects of activation of the magnesium, temperature, concentration of the alkyl halide, magnesium to alkyl halide ratio, magnesium purity, the nature of the alkyl group, the nature of the halide group, and solvent (viscosity and basicity) on the formation of Grignard reagent were studied.The data obtained were used to test the earlier report by Garst that alkyl radicals, generated in the reaction of an alkyl halide with magnesium, diffuse freely into the solvent phase and return to the magnesium surface to form Grignard reagent.In this study cyclizable radical probes and radical traps were employed to study the extent to which radicals leave and return to the surface of magnesium to form Grignard reagent.In the particular system reported here, the data indicate that ca.25percent of the Grignard reagent is formed from radicals that diffuse into the solvent phase and than return to the magnesium surface to form Grignard reagent.
- Ashby, E. C.,Oswald, John
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p. 6068 - 6076
(2007/10/02)
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- HOMOLYTIC DISPLACEMENT AT CARBON. XI. INTRAMOLECULAR HOMOLYTIC DISPLACEMENT AS A ROUTE TO CYCLOPENTANE AND TETRAHYDROFURAN DERIVATIVES FROM HEX-5-ENYL- AND HEX-3-OXO-5-ENYLCOBALOXIMES
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5-Methylhex-5-enylcobaloxime reacts with carbon tetrachloride and with fluorotrichloromethane at 80-100 deg C to give substantially pure 1-methyl-1-(Β,Β,Β-trichloroethyl)- and 1-methyl-1-(β-fluoro-β,β-dichloroethyl)-cyclopentane.Hex-5-enylcobaloxime also gives trichloroethylcyclopentane from carbon tetrachloride, but the yield is dependent on the concentration of carbon tetrachloride.Similar cyclisation to give trichloroethyl- or fluorodichloroethyltetrahydrofuran is observed in the reactions of hex-3-oxo-5-enylcobaloxime with carbon tetrachloride and fluorotrichloromethane.However, no cyclisation was observed in the reactions of the ester, hex-2-one-3-oxo-5-enylcobaloxime, with carbon tetrachloride.These reactions are believed to take place by attack of a polyhalogenomethyl radical at the terminal unsaturated carbon of the organic ligand, followed either by an intramolecular homolytic displacement in which the carbon radical at position-5 attacks carbon-1 with displacement of cobaloxime(II), or by a halogen atom abstraction.
- Bongars, Christophe,Bougeard, Peter,Bury, Adrian,Cooksey, Christopher J.,Johnson, Michael D.,et al.
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p. 163 - 172
(2007/10/02)
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- FREE RADICAL REARRANGEMENTS OF ORGANOCOBALOXIMES: ALKYNYL TO CYCLOALKYLIDENE AND HEXENYL TO CYCLOPENTYLMETHYL
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Under irradiation by tungsten light in pyridine solution, several substituted alkylcobaloximes undergo rearrangement to more stable substituted alkyl- or alkenyl-cobaloximes.When the same reactions are carried out in the presence of carbon tetrachloride or chloroform, no rearranged organobaloximes are obtained, but a variety of organic products are obtained derived from the interception of transient organic radicals by the halogenated solvent.The rearrangements are rationalised in terms of a reversible homolysis of the carbon-cobalt bond, rearrangement of the organic radical and recapture by the cobalt(II) fragment to give complexes that are more stable to irradiation than their precursors.
- Bougeard, Peter,Cooksey, Christopher J.,Johnson, Michael D.,Lewin, Melanie J.,Mitchell, Stewart,Owens, Paul A.
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p. 349 - 358
(2007/10/02)
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- Occurrence of Electron Transfer in the Reduction of Organic Halides by LiAlH4 and AlH3
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A variety of methods have been utilized to detect the occurrence of a single electron transfer pathway in the reduction of alkyl halides by LiAlH4 and AlH3, i.e., (1) product studies of reduction of cyclizable alkyl halides containing the 5-hexenyl group, (2) trapping of intermediate radicals by dicyclohexylphosphine and other trapping agents, (3) direct EPR observation of the trityl radical in the reduction of trityl bromide, and (4) stereochemical studies of the reduction of secondary halides by lithium aluminum deuteride.The extent of electron transfer was found to be a function of the solvent, the substrate, the leaving group, and the hydride reagent.For alkyl iodides, and to a lesser extent bromides, electron transfer was found to be the major reaction pathway; however, no evidence for electron transfer was found for the corresponding chlorides or tosylates.Reduction of (+)-2-octyl iodide by LiAlD4 was found to be much less stereospecific than the corresponding reduction of bromide, chloride, or tosylate, indicating intermediate radical formation in the reduction of the secondary iodide.
- Ashby, E. C.,DePriest, R. N.,Goel, A. B.,Wenderoth, Bernd,Pham, Tung N.
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p. 3545 - 3556
(2007/10/02)
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