Asymmetric synthesis of 2-alkenyl-1-cyclopentanols via tin-lithium exchange and intramolecular cycloalkylation

[reaction: see text] We report a method for the synthesis of chiral cyclopentanes using tin-lithium exchange and cycloalkylation reactions. The sec-butyllithium/(-)-sparteine-mediated deprotonation of an alkyl carbamate and subsequent substitution furnishes a highly enantioenriched stannane as a stable carbanion equivalent. It was transformed into suitable cyclization precursors, which underwent tin-lithium exchange and stereoselective cycloalkylation when reacted with n-butyllithium, giving highly enantioenriched cyclopentanes in very good yields. A kinetic resolution was observed with a higher substituted stannane.     

Asymmetric synthesis of (2-carbamoyloxy-1-alkenyl)cyclopropanes by intramolecular cycloalkylation

Enantioenriched, diastereomerically pure (2-carbamoyloxy-1-alkenyl)cyclopropanes 22 are easily prepared via deprotonation of different allyl carbamates with n-butyllithium and (−)-sparteine (4). The mechanism of the cyclization reaction was determined and several substituted (S)-configured vinylcyclopropanes 32 were synthesized by two different methods. The configurational stability of the intermediate lithiated allyl carbamates and the half-time of epimerization were investigated in a series of silylation experiments, achieving up to 90% ee in the kinetically controlled enantiotopos-differentiating deprotonation.     

Asymmetric synthesis of a (2Z,7E)-cyclononadiene by an intramolecular cycloalkylation and insight to its conformational properties

Here, we report a novel synthesis of a monosubstituted, enantio- and diastereomerically enriched trans-cyclononadienol. The reaction consists of an enantioselective (-)-sparteine-mediated allylic lithiation of an achiral 7-chlorononadienyl carbamate and a subsequent stereospecific intramolecular allyllithium-allyl chloride coupling. The stereochemical course of the cyclization has been determined, and the high configurative stability of the chiral nine-membered carbocycle has been investigated by kinetic measurements and rationalized by computational calculations.     

Hydrogen isotope exchange of polymethylferrocenes with acids

Conclusions The rate of isotope exchange of the ring hydrogen atoms in hexamethylferrocene is 10⁴ times greater than for unsubstituted ferrocene, while this rate for octamethylferrocene is 10⁵ times greater than for unsubstituted ferrocene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2389–2390, October, 1984.     

Hydrogen exchange of molybdenum tricarbonyl triphenylphosphonium cyclopentadienylide

Conclusions Molybdenum tricarbonyl triphenylphosphonium cyclopentadienylide enters into the hydrogen exchange reaction with deuteroethanol in neutral medium with the same speed as the uncomplexed ylid corresponding to it.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1375–1376, June, 1973.The mass spectra were taken and analyzed by N. I. Vasyukova, for which we are grateful.     

Hydrogen exchange and hydration dynamics in gelatin gels

Gelatin, derived from the collagen triple helix, is the most widely used functional biopolymer and a prototype for studies of physical gels. Gelatin gels have also served as models for soft biological tissue in efforts to elucidate the molecular basis of the magnetic relaxation phenomena that govern magnetic resonance image contrast. Yet, the microstructure, hydration, and magnetic relaxation behavior of gelatin gels are not well understood. To address these issues, we report here the water 2H and 17O magnetic relaxation dispersion (MRD) profiles from gelatin gels over wide ranges of resonance frequency and pH. For the global analysis of this extensive data set, we use a generalized relaxation theory that remains valid for arbitrarily slow molecular dynamics. The strong pH dependence in the 2H profiles can be rationalized quantitatively as the result of exchange with bulk water of labile hydrogens in gelatin side chains. The global analysis of the MRD data yields hydrogen-exchange rate constants, acid dissociation constants, and orientational order parameters in agreement with independent structural, thermodynamic, and kinetic data. The MRD analysis reveals a highly mobile hydration layer at the surface of the gelatin triple helix and a small number of trapped water molecules with residence times on the order of 10(-8) s, presumably associated with structural defects and branch points in the gel. The MRD data also indicate that approximately 20% of the gelatin residues belong to flexible polypeptide chains, rather than to rigid triple-helical segments. By identifying the molecular species and motions responsible for the 2H and 17O dispersion profiles, this study takes a significant step toward a quantitative understanding of water relaxation in aqueous gels and biological tissue.     

Hydrogen exchange in benzamidoximes studied by NMR spectroscopy

The hydrogen exchange process in benzamidoximes ( 1 and 2 ) was studied over a range of temperature and a determination of the activation parameter ΔG? for this process was made.     

Hydrogen and chlorine isotope exchange in N-Methylimidazolium chloride

Isotope exchange of deuterium and³⁶Cl between N-methylimidazolium chloride and gaseus hydrogen chloride has been studied over the temperature range of 249–322 K. A mechanism of exchange for both atmos is proposed and the equilibrium isotope effect of deuterium accompanying this reaction is discussed.     

Kinetics of hydrogen isotope exchange in molecules with strong intramolecular hydrogen bonds

Rate constants and activation energies of hydrogen exchange in solution between methanol and molecules with intramolecular H-bonds have been measured. It has been established that the rate-determining step is the dissociation of this bond.

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Effect of a metal ion on intramolecular spin exchange in spin-labeled complexes

The characteristic features of intramolecular spin exchange in 14 complexes of Ag^I, Hg^II, Ni^II, Pd^II, Pt^II, Au^III, and Pt^IV with spin-labeled ligands were studied by ESR spectroscopy. The measured values of the exchange integral ‖J‖ and the differences between the enthalpies of the efficient conformations (ΔH) were compared with the electronic polarization (refraction)R _f of the Ni^II, Pd^II, and Pt^II ions and Klopman's rigidity parameters σ_K, which characterize the total polarazibility of the ions and the degree of covalence of the bond between the metal atom and the donor atom of the ligand, respectively. Delocalization of the electron spin density and the efficiency of spin exchange are determined by the relative contributions of the s, p, and d orbitals, which produce the overlap integral of wave functions, ‖J‖, and by the geometric features of the coordination polyhedron, which affect the mutual orientation of the N−O fragments. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2005–2009, October, 1999.     

Solvent-controlled regioselectivity in the ortho-palladation of benzylamines and intramolecular exchange in cyclopalladated ligands

Conclusions Cyclometallation of 1-(3,4-dimethoxyphenyl)-2-methyl-3-(4-nitrophenyl)-2-azapropane upon treatment with Pd(II) acetate occurs at the electron rich dimethoxy-substituted aromatic ring in CHCl₃ solution, and at the electron poor nitrophenyl ring in AcOH solution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 175–181, January, 1988.     

Synthesis of sultams by cycloalkylation of (alkoxycarbonylmethane)sulfonanilides

(Methoxycarbonylmethane)sulfonanilides are alkylated by α, ω-dihaloalkanes in K₂CO₃-DMF with the formation of sultams. A high sensitivity has been detected for the reaction rate on the electronic effect of substituents in the aromatic nucleus, although substituents in the ortho position do not obstruct the reaction and in the case of 2,6-disubstituted derivatives the reaction rate and sultam yield were maximal. Tertiary sulfonamides form derivatives of 1-sulfamoylcyclopropanecarboxylic acid under these conditions. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 605–617, April, 2008.     

Hydrogen isotope exchange and separation in gas-solid phase systems

Systems of two or more hydrogen-containing phases in solution equilibrium with hydrogen may not be in isotopic equilibrium. The resulting exchange of hydrogen isotopes between the phases is discussed with respect to both the kinetic behaviour and the final equilibrium state. The advantages of tracer experiments using tritium are discussed in terms of the experimental arrangement and the information attainable. It is shown that the equilibrium separation factor reflects the state of the dissolved hydrogen in different sorption states and that the exchange kinetics are affected by the state of the interphase. The effect of the total hydrogen pressure on the tracer exchange with tritium is discussed. The relationships developed are applied to the metal-hydrogen systems PdH_n and Ti_0.4Mn_0.6H_n. The results are supplemented by pressure-composition isotherms, neutron vibrational spectra, scanning electron micrographs, Auger electron spectra and Auger electron spectroscopy depth profiles obtained using argon ions.     

Hydrogen and chlorine isotope exchange in hydrogen dichloride ions

The kinetics of deuterium and chlorine-36 isotope exchange between hydrogen dichloride ions in tetramethyl- and tetraethyl-ammonium salts and hydrogen chloride has been studied in the temperature range 275–304 K. On the basis of the results obtained the exchange mechanism was proposed emphasizing the role of hydrogen bonding in the exchange process.