Studies on the Thorpe-Ziegler-reaction. A new synthesis of the pyridine part of thiamine]

Thorpe-Ziegler cyclization of N′-cyano-N-(2-cyanoethyl)-acetamidine ( 5a ) yields 4-amino-2-methyl-1,6-dihydro-5-pyrimidinecarbonitrile ( 8a ). The acetamidine 5a is accessible either from the N-cyanoimidate 1 and β-aminopropionitrile ( 3a ) or the N-cyanoamidine 2 and acrylonitrile ( 4 ). The dihydropyrimidine 8a is easily converted to 4-amino-2-methyl-5-pyrimidine-carbonitrile ( 13 ) by dehydrogenation or to 4-amino-5-aminomethyl-2-methylpyrimidine ( 15 ) by hydrogenation-dehydrogenation. Both products are important intermediates in the synthesis of thiamine.     

Synthesis of 4,5-benzotropones by cyclization of 1,3-bis-silyl enol ethers with 1,2-dialdehydes

The cyclization of 1,3-bis-silyl enol ethers or (2,4-dioxobutylidene)triphenylphosphoranes with phthalic dialdehyde allowed a convenient synthesis of a variety of 4,5-benzotropones. The hydrogenation of benzotropones afforded functionalized benzocycloheptanones which were transformed into tricyclic butenolides.     

Photoelectron imaging of helium droplets

The photoionization and photoelectron spectroscopy of He nanodroplets (10(4) atoms) has been studied by photoelectron imaging with photon energies from 22.5-24.5 eV. Total electron yield measurements reveal broad features, whose onset is approximately 1.5 eV below the ionization potential of atomic He. The photoelectron spectra are dominated by very low energy electrons, with less than 0.6 meV. These results are attributed to the formation and autoionization of highly vibrationally excited He(*)(n) Rydberg states within the cluster, followed by strong final state interactions between the photoelectron and the droplet.     

Reductive desulfurization of allylic thiols by HS-/H2S in water gives clue to chemical reactions widespread in natural environments

The reduction of allylic thiols to alkenes by hydrogen sulfide in aqueous solutions, a novel reaction that may explain reduction processes widely occurring in natural environments, has been discovered. Its mechanism has been studied and suggested to follow an S(RN)1-like pathway involving radical intermediates undergoing 1,4 hydrogen shifts. [reaction: see text]     

Detection of ppm quantities of gaseous SO2 by o9rganoplatinum dendritic sites immobilised on a quartz microbalance

Sensor devices for the detection of low quantities of SO2 gas have been constructed which comprise organoplatinum receptor sites for the selective recognition of SO2 and a quartz crystal microbalance for the detection of small mass changes at the receptor sites.     

Spectrum of interpolated operators

Let be a compatible pair of Banach spaces and let be an operator that acts boundedly on both and . Let be the corresponding operator on the complex interpolation space .

The aim of this paper is to study the spectral properties of . We show that in general the set-valued function is discontinuous even in inner points and show that each operator satisfies the local uniqueness-of-resolvent condition of Ransford. Further we study connections with the real interpolation method.

     

Evidence of Hofstadter's Fractal Energy Spectrum in the Quantized Hall Conductance

The energy spectrum of a two-dimensional electron system in a perpendicular homogeneous magnetic field and a weak lateral superlattice potential with square symmetry is composed of Landau bands with recursive internal subband structure. The Hall conductance in the minigaps is anticipated to be quantized in integer multiples of e(2)/h that vary erratically from minigap to minigap in accordance with a Diophantine equation. Hall measurements on samples with the requisite properties uncover this long searched for evidence of Hofstadter's butterflylike energy spectrum.     

Ferromagnetic hcp chromium in Cr/Ru(0001) superlattices

We report the first observation of a weak ferromagnetic state of Cr in Cr/Ru(0001) superlattices, based on magnetic hysteresis and corroborated by x-ray magnetic circular dichroism at the CrL(2,3) edges. In situ reflection high-energy electron diffraction, x-ray diffraction, and Cr K-edge polarized x-ray absorption investigations have shown that the Cr layers thinner than 8 angstroms adopt a slightly distorted hcp structure, accompanied by a large atomic volume expansion of up to 14% compared to the bcc packing volume. The expanded hcp structure clearly induces the observed ferromagnetism, in agreement with theory.