Ring-Closing Metathesis Strategies to P -heterocycles

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.     

Diterpenoids

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.     

Conformationally constrained alpha-boc-aminophosphonates via transition metal-catalyzed/curtius rearrangement strategies

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.     

Out-of-equilibrium Kondo effect in a mesoscopic device

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.     

Electric field effects on quasi-coherent energy transfer

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.     

Spectinabilin,a new nitro-containing metabolite isolated from streptomyces spectabilis

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.     

The nature of energy delocalization in molecular crystals

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.