- Deuterium and Tritium Labeling with the Zinc-Sodium Iodide Method
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Primary and secondary hydroxyl groups can be replaced by deuterium or tritium when the corresponding sulfonate esters are reduced with zinc, sodium iodide, and deuterium or tritium oxide in 1,2-dimethoxyethane.The method tolerates a variety of other reducible functionalities, namely, α,β-enone, ketone, and ester.The labeling can be conducted with a high regiospecificity in the presence of enolizable hydrogens.The method is less satisfactory for a stereospecific replacement of secondary hydroxyl groups, yielding mixtures of stereoisomers and olefins as byproducts.The distribution of the stereoisomers depends on the rate of configurational inversion in the intermediary iodides arising by displacement of the original tosyloxy group.Deuterium NMR spectra and their use in the configurational assignment are discussed.
- Turecek, Frantisek,Veres, Karel,Kocovsky, Pavel,Pouzar, Vladimir,Fajkos, Jan
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- The quasi-homo-anomeric interaction in substituted tetrahydropyranyl radicals: Diastereoselectivity
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The isomer distribution of products from the reaction of a range of simple cyclohexyl and tetrahydropyranyl radicals (3 - 7) with Bu3SnD and with allyltributyltin, has been determined in order to gauge the influence of the classical anomeric ef
- Beckwith, Athelstan L.J.,Duggan, Peter J.
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- Stereoselective Retentive Domino Transmetalations of Secondary Alkyllithium Compounds to Functionalized Secondary Alkylcopper Reagents
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Functionalized secondary alkyllithium reagents obtained by I/Li exchange from the corresponding secondary alkyl iodides undergo two successive transmetalations with Me3SiCH2ZnBr.LiBr and CuBr.2LiCl.Me2S to provide functionalized secondary alkylcopper compounds with high retention of configuration. These alkylcopper derivatives react further with electrophiles such as alkynyl esters, acid chlorides, allylic chlorides, ketals, ethylene oxide, and 3-iodocyclopentanone with high retention of configuration. A related sequence of transmetalations with MeMgI and LaCl3.2LiCl allows a retentive addition of secondary alkyllithium reagents to acetone. The influence of the solvent on the configurational stability of secondary alkylzinc reagents is described.
- Moriya, Kohei,Simon, Meike,Mose, Rasmus,Karaghiosoff, Konstantin,Knochel, Paul
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supporting information
p. 10963 - 10967
(2015/09/15)
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- Preparation of stereodefined secondary alkyllithium compounds
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We have developed a practical stereoretentive iodine/lithium-exchange process that allows the stereodefined preparation of cis- and trans-cycloalkyllithium compounds from their corresponding stereodefined iodides. Quenching with electrophiles offers stere
- Seel, Stephanie,Dagousset, Guillaume,Thaler, Tobias,Frischmuth, Annette,Karaghiosoff, Konstantin,Zipse, Hendrik,Knochel, Paul
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p. 4614 - 4622
(2013/05/08)
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- Preparation and reactivity of chiral β-amino-alkylzinc iodides and related configurationally stable zinc organometallics
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Several zinc organometallics bearing at the β-position a carbamate or an amido function with an acidic N-H group were prepared using the direct insertion of zinc dust into the corresponding alkyl iodides in THF or THF:DMSO mixtures. Most of the starting iodides were obtained from natural α-amino acids and the resulting zinc species afforded after transmetalation with CuCN.2LiCl and reaction with a selection of relatively reactive electrophiles a variety of polyfunctional 1,2-amino alcohol derivatives and carbamates in optically pure form. Several secondary β-amido alkyl iodides were converted to the corresponding chiral zinc reagents and trapped with electrophiles. The configurational stability of chiral secondary organozinc compounds and the stereochemical course of their reactions were examined.
- Duddu,Eckhardt,Furlong,Knoess,Berger,Knochel
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p. 2415 - 2432
(2007/10/02)
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- Diastereofacial selectivity in reactions of substituted cyclohexyl radicals. An experimental and theoretical study
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The diastereofacial selectivity in reactions of a series of alkyl-substituted cyclohexyl radicals has been investigated. In additions of cyclohexyl radicals to alkenes, it has been found that only substituents bound at the olefinic center being attacked by the radical influence the equatorial-axial selectivity. Substituents bound to the radical center or axial substituents β to the radical center lead to increased axial attack. Equatorial β-substituents or axial γ-substituents increase the amount of equatorial attack. The same trends are observed for halogen and hydrogen abstraction reactions; the amount of axial reaction product is usually somewhat higher than in the addition reactions. The stereoselectivities can be explained with steric and torsional effects very similar to those suggested for nucleophilic addition reactions to cyclohexanones. A MM2 force field has been parameterized to gain further insight into the stereochemistry of the reaction.
- Damm,Giese,Hartung,Hasskerl,Houk,Hüter,Zipse
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p. 4067 - 4079
(2007/10/02)
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- MECHANISMS OF FREE-RADICAL REACTIONS. XVIII. STEREOSELECTIVITY OF THE TRANSFER OF A HYDROGEN ATOM DURING THE FREE-RADICAL REDUCTION OF SUBSTITUTED CYCLOHEXYL HALIDES
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The stereochemistry of the free-radical reduction of cis- and trans-4-tert-butylcyclohexyl halides by trialkyldeuterostannanes R3SnD was studied.Irrespective of the nature of the halogen atom (bromine or chlorine) and the stereochemistry of the initial halide, the predominant reaction product is cis-4-deutero-tert-butylcyclohexane with axial orientation of the deuterium atom ( cca 80percent, 13C NMR).The stereoselectivity of the transfer of the deuterium atom to the 4-tert-butylcyclohexyl radical is determined by the torsial strain in the transition state.The reduction of 1,4-dimethylcyclohexyl chloride by the reagents R3EH (E=Sn, Ge) gives a mixture of trans(e,e)- and cis(e,a)-1,4-dimethylcyclohexanes richer in the trans isomer.
- Dneprovskii, A. S.,Pertsikov, B. Z.,Chertkov, V. A.
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p. 291 - 294
(2007/10/02)
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- Studies on the Mechanism of Transition-Metal-Assisted Sodium Borohydride and Lithium Aluminium Hydride Reductions
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Studies on the course of transition-metal-assisted NaBH4 and LiAlH4 reductions of (1) nitriles, (2) alkenes, and (3) alkyl halides are described. (1) The kinetics of benzonitrile (PhCN) reduction indicate that at high nitrile:catalyst ratios, the rate of reduction is independent of PhCN concentrations.Furthermore, the rate of PhCN reduction exhibits a first-order dependence on NaBH4 concentration, as measured over a fourfold range of BH4(1-) concentration and several half-lives of PhCN.Moreover, when PhCN was reduced with equimolar mixtures of NaBH4 and NaBD4, a significant primary kinetic isotope effect was observed.Rapid complexation of PhCN to be boride surface apparently activates the nitrile group toward rate-determining hydride addition from dissolved, uncoordinated NaBH4. (2) The selective reduction of alkenes by NaBH4-CoCl2 is attributed to adventitious heterogeneous catalytic hydrogenation. (3) The combination of LiAlH4 with CoCl2 forms a black precipitate of cobalt aluminide (CoAl) which was isolated, analyzed by atomic absorption spectroscopy, and shown to play an essential catalytic role in the reduction of alkyl halides.Labeling experiments demonstrate stereochemical randomization by a heterogeneous process involving solvent as the hydrogen donor and LiAlH4 as a co-reductant.A radical mechanism involving halide atom transfer or oxidative addition to the aluminide is proposed.
- Osby, John O.,Heinzman, Stephen W.,Ganem, Bruce
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- Stereochemistry of the Reactions of Lithium Di-tert-butylbiphenyl with Alkyl Halides
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The stereochemistry of the reaction of lithium di-tert-butylbiphenyl with cyclopropyl halides, 7-chloronorcarane, 7-bromo-7-methylnorcarane, and anti-3-chloro-exo-tricyclo2,4>octane generated syn/anti lithio reagent ratios of 1:10, 3:1, and 200:1, respectively.Similar treatment of noncyclopropyl secondary halides syn-7-bromonorbornene, anti-7-bromobenzonorbornadiene, exo-2-chloronorbornane, and 4-chloro-tert-butylcyclohexane resulted in lithio reagent ratios of 1:3.8 (syn/anti), 1:1,33 (syn/anti), 10:1 (exo/endo), and 1:14 (cis/trans), respectively.For the cyclopropyl radicals generated in the first group, the lithio reagent ratios describe the related radical equilibrium; the significance of the stereochemistry of the reaction of LiDBB with noncyclopropyl secondary halides is discussed in terms of both precursor radicals and carbanions.
- Freeman, Peter K.,Hutchinson, Larry L.
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p. 4705 - 4713
(2007/10/02)
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- 2H Nuclear Magnetic Resonance Study of the Stereochemistry of Reduction of Some Organomercurials
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The stereochemical courses of the replacement of mercury by deuterium in a range of organomercury halides or acetates, by employing as reducing systems sodium borodeuteride/tetrahydrofuran/aqueous base and 1-2percent sodium amalgam/ deuterium oxide/ sodiu
- Kitching, William,Atkins, Annette R.,Wickham, Geoffrey,Alberts, Vince
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p. 563 - 570
(2007/10/02)
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