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81.
82.
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. 相似文献
83.
Albrecht Pietsch 《Mathematische Annalen》1980,247(2):169-178
84.
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. 相似文献
85.
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. 相似文献
86.
87.
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] 相似文献
88.
Albrecht M Schlupp M Bargon J van Koten G 《Chemical communications (Cambridge, England)》2001,(18):1874-1875
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. 相似文献
89.
Ernst Albrecht Vladimir Mü ller 《Proceedings of the American Mathematical Society》2001,129(3):807-814
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.
90.
Albrecht C Smet JH von Klitzing K Weiss D Umansky V Schweizer H 《Physical review letters》2001,86(1):147-150
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. 相似文献