Alicyclic-Amine-Derived Imine-BF3 Complexes: Easy-to-Make Building Blocks for the Synthesis of Valuable α-Functionalized Azacycles

A new strategy to access α-functionalized alicyclic amines via their corresponding imine-BF₃ complexes is reported. Isolable imine-BF₃ complexes, readily prepared via dehydrohalogenation of N-bromoamines in a base-promoted/18-crown-6 catalyzed process followed by addition of boron trifluoride etherate, undergo reactions with a wide range of organometallic nucleophiles to afford α-functionalized azacycles. Organozinc and organomagnesium nucleophiles add at ambient temperatures, obviating the need for cryogenic conditions. In situ preparation of imine-BF₃ complexes provides access to α-functionalized morpholines and piperazines directly from their parent amines in a single operation. α-Functionalized morpholines can be elaborated further, for instance by installing a second substituent in the α′-position.     

Self-chemical ionization of diethylzinc

The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd.     

Gasanalyse

Ohne Zusammenfassung     

Fast numerical method for the solution of the quasigeostrophic vorticity equation

Particle methods are typically O(N²), where N is the number of computational elements. We present an O(N) particle method for the equations for the conservation of potential vorticity. This method is based on the idea of grouping the particles. The necessary expansions and truncation errors are given. The accuracy and speed of the method are presented for both scalar and vector machines. © 1993 John Wiley & Sons, Inc.     

Some properties of the magnetic moments of the Δ′s in QCD

Zeitschrift für Physik C Particles and Fields - The three experimental findings namely, deficits in the solar and atmospheric neutrino fluxes and the need for a significant hot component in...     

Hydrogen storage in novel organometallic buckyballs

Transition metal (TM) atoms bound to fullerenes are proposed as adsorbents for high density, room temperature, ambient pressure storage of hydrogen. C60 or C48B12 disperses TMs by charge transfer interactions to produce stable organometallic buckyballs (OBBs). A particular scandium OBB can bind as many as 11 hydrogen atoms per TM, ten of which are in the form of dihydrogen that can be adsorbed and desorbed reversibly. In this case, the calculated binding energy is about 0.3 eV/H(2), which is ideal for use on board vehicles. The theoretical maximum retrievable H2 storage density is approximately 9 wt %.     

A crystallization-induced stereoselective glycosidation reaction in the synthesis of the anticancer drug etoposide

The anticancer drug etoposide, 1, is prepared in 79% overall yield from readily available 4'-demethyl-4-epipodophyllotoxin, 3, and 4, 6-O-ethylidene-2,3-O-dibenzyl-D-glucose, 4, via a crystallization-induced stereoselective glycosidation reaction followed by catalytic hydrogenation.     

An impact theory for Doppler and pressure broadening—I. General theory

A quantum-mechanical impact theory for the combined effects of Doppler and pressure broadening is developed from quantum radiation theory. The results are compared with other semiclassical theories and certain simplifying approximations relevant to cases of experimental and theoretical interest are discussed.     

Pion pair production in photon-photon collisions at spear

We report a measurement of the cross section for the process γγ→π⁺π^? at invariant masses 500 MeV/c² < m_ππ<2000 MeV/c². A value for the radiative width of the f(1270) tensor meson Γ_f→γγ = 3.6 ± 0.3 ± 0.5 KeV (helicity λ = 2) has been obtained from a fit to the observed ππ mass spectrum.     

Electronic energy band parameters of graphite and their dependence on pressure,temperature and acceptor concentration

An analysis has been made of experimental data on the dependence of electronic properties of graphite on pressure and acceptor concentration, using the Slonczewski-Weiss dispersion relationship for the free carriers. It is shown that such experiments cannot be interpreted adequately without taking into account all of the band-overlap parameters in this theory. Previous workers had particularly neglected the influence of the parameter γ₃, which trigonally warps the constant energy surfaces. The results presented will also be useful for interpreting new experiments in which either the band overlap parameters or the Fermi-energy are changed. A discussion of possible changes in band parameters with temperature is included.