Palladium(0)-catalyzed cyclization of electron-deficient enynes and enediynes

In the presence of a Pd(0) precatalyst, Pd2(bq)2(nbe)2 or Pd2(dba)3, 1,6-enyne esters were heated in refluxing benzene to give cyclodimers as single regioisomers. On the other hand, the combination of the Pd(0) precatalyst and triphenyl phosphite gave rise to various cycloisomerization products depending on the substitution pattern of the enyne esters. Six-membered ring cycloisomerization products were predominantly obtained from enyne esters bearing methallyl or 2-phenyl-2-propenyl moieties, while other enyne esters afforded normal five-membered ring cycloisomerization products. Intramolecular [2 + 2 + 2] cyclocotrimerization of enediyne esters also proceeded in the presence of the Pd(0) precatalyst and triphenylphosphine to give fused cyclohexadienes.     

Use of a chiral praseodymium shift reagent in predicting the complete stereostructure of glisoprenin A

[structure: see text] The complete stereostructure of glisoprenin A has been predicted via analysis of the 13C NMR behaviors in the presence of (R)- and (S)-Pr(tfc)3.     

Spin-flop transition and the anisotropic magnetoresistance of Pr(1.3-x)La(0.7)CexCuO4: unexpectedly strong spin-charge coupling in the electron-doped cuprates

We use transport and neutron-scattering measurements to show that a magnetic-field-induced transition from noncollinear to collinear spin arrangement in adjacent CuO2 planes of lightly electron-doped Pr(1.3-x)La(0.7)CexCuO4 (x=0.01) crystals affects significantly both the in-plane and out-of-plane resistivity. In the high-field collinear state, the magnetoresistance (MR) does not saturate but exhibits an intriguing fourfold-symmetric angular dependence, oscillating from being positive at B//[100] to being negative at B//[110]. The observed MR of more than 30% at low temperatures induced by a modest modification of the spin structure indicates an unexpectedly strong spin-charge coupling in electron-doped cuprates.     

Absolute stereostructures of polypodane-type triterpenes, myrrhanol A and myrrhanone A, from guggul-gum resin (the resin of Balsamodendron mukul)

Two new polypodane-type triterpenes, myrrhanol A and myrrhanone A, were isolated from the 50% aqueous methanolic extract of guggul-gum resin [the resin of Balsamodendron (=Commiphora) mukul HOOK]. The structures of the new constituents, including their absolute configurations, were determined on the basis of chemical and physicochemical evidence.     

Reaction of poly(vinyl alcohol) with pentavalent vanadium ion

The reaction of poly(vinyl alcohol) (PVAL) with V(V), i.e., pentavalent vanadium ion, was studied in aqueous H₂SO₄ medium. The viscosity change of reaction mixture with time showed a peculiar feature owing to formation of labile complex between V(V) and PVAL and the subsequent decomposition of the complex. On the other hand, the change of viscosity disappeared when NaOH was added during the reaction to neutralize H₂SO₄ in the reaction mixture. Under a suitable condition, the reaction mixture set to a gel as a result of complex formation. It appeared that reactive sites in PVAL responsive to complexing with V(V) were 1,2-glycol unit and 1,2-ketoalcohol unit resulting from the oxidation of 1,2-glycol by V(V). The rate of oxidation was increased with increasing H₂SO₄ concentration. The main-chain scission of PVAL took place to an insignificant extent, unless the reaction condition was severe. Based on the results obtained a reaction mechanism has been proposed.     

Observation of the acceleration of a single bunch by using the induction device in the KEK proton synchrotron

A single rf bunch in the KEK proton synchrotron was accelerated with an induction acceleration method from the injection energy of 500 MeV to 5 GeV.