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51.
Kevin T. Sprott Matthew D. McReynolds Paul R. Hanson 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1807-1809
A general approach to the synthesis of P -heterocycles using the ring-closing metathesis reaction is described. We have developed a new method utilizing phosphorus nuclei as suitable temporary tethers for the coupling of non-racemic allylic amines. This approach allows for the generation of symmetric and unsymmetric 1,4-diamines. Subsequent coupling of these 1,4-diamines with various nuclei produces an array of 7-membered heterocycles. 相似文献
52.
53.
Hanson JR 《Natural product reports》2002,19(2):125-132
The review covers the isolation and chemistry of diterpenoids including labdanes, clerodanes, pimaranes, abietanes, kauranes, gibberellins, cembranolides, taxanes and marine diterpenoids. The literature from January to December 2000 is reviewed and 157 references are cited. 相似文献
54.
A transition metal-catalyzed/Curtius rearrangement sequence toward the development of conformationally constrained alpha-Boc-aminophosphonates 2-6 is described. An approach using the versatile tert-butylphosphonoacetate moieties 1a and 1b to derive an array of mono- and bicyclic alpha-Boc-aminophosphonate systems is presented. Conformational constraint is incorporated using either the ring-closing metathesis reaction catalyzed by the first generation Grubbs catalyst or intramolecular cyclopropanation mediated by Rh2(OAc)4. Using the tert-butyl ester functionality in 1a or 1b as a potential amino group, the Curtius rearrangement provides an efficient route toward the target alpha-Boc-aminophosphonates. 相似文献
55.
De Franceschi S Hanson R Van Der Wiel WG Elzerman JM Wijpkema JJ Fujisawa T Tarucha S Kouwenhoven LP 《Physical review letters》2002,89(15):156801
We study the nonequilibrium regime of the Kondo effect in a quantum dot laterally coupled to a narrow wire. We observe a split Kondo resonance when a finite bias voltage is imposed across the wire. The splitting is attributed to the creation of a double-step Fermi distribution function in the wire. Kondo correlations are strongly suppressed when the voltage across the wire exceeds the Kondo temperature. A perpendicular magnetic field enables us to selectively control the coupling between the dot and the two Fermi seas in the wire. Already at fields of order 0.1 T only the Kondo resonance associated with the strongly coupled reservoir survives. 相似文献
56.
57.
The effect of an external electric field on the rate of electronic excitation energy transfer in a model molecular crystal system is shown to depend on the nature of the site-to-site transfer and on whether the directional coherence is limited by phonon scattering or by defect scattering processes. 相似文献
58.
A new nitro-containing metabolite, spectinabilin, was isolated from the crude streptovaricin complex produced by Streptomyces spectabilis. The structure was determined by degradation studies and spectral properties. A possible biosynthetic pathway of the metabolite is discussed in relation to the biosynthesis of the streptovaricins. 相似文献
59.
The eigenfrequencies for the lowest triplet state of the naphthalene resonance pair hamiltonian are calculated and compared with optical and magnetic resonance data. The importance of both coherent and incoherent processes in understanding exciton spectra is emphasized. 相似文献
60.
Hanson RJ Macomber HK Morrison AC Boucher MA 《The Journal of the Acoustical Society of America》2005,117(1):400-412
The purpose of the work reported here is to further experimentally explore the wide variety of behaviors exhibited by driven vibrating wires, primarily in the nonlinear regime. When the wire is driven near a resonant frequency, it is found that most such behaviors are significantly affected by the splitting of the resonant frequency and by the existence of a "characteristic" axis associated with each split frequency. It is shown that frequency splitting decreases with increasing wire tension and can be altered by twisting. Two methods are described for determining the orientation of characteristic axes. Evidence is provided, with a possible explanation, that each axis has the same orientation everywhere along the wire. Frequency response data exhibiting nonlinear generation of transverse motion perpendicular to the driving direction, hysteresis, linear generation of perpendicular motion (sometimes tubular), and generation of motion at harmonics of the driving frequency are exhibited and discussed. Also reported under seemingly unchanging conditions are abrupt large changes in the harmonic content of the motion that sometimes involve large subharmonics and harmonics thereof. Slow transitions from one stable state of vibration to another and quasiperiodic motions are also exhibited. Possible musical significance is discussed. 相似文献