Rhodium-catalyzed cyclopropanation using ene-yne-imino ether compounds as precursors of (2-pyrrolyl)carbenoids

[reaction: see text] The reaction of alkenes with conjugated ene-yne-imino ether or ene-yne-aldimine in the presence of a catalytic amount of [Rh(OAc)(2)](2) gives (2-pyrrolyl)cyclopropanes in good yields. The key intermediate of this cyclopropanation is a (2-pyrrolyl)carbenoid generated by the nucleophilic attack of imine nitrogen atom at an internal alkyne carbon activated by rhodium complex. The intramolecular reaction also proceeds to afford a polycyclic pyrrole.     

A Pb MAS-NMR study of Pb-containing glasses

²⁰⁷Pb magic angle spinning (MAS)-NMR spectra have been obtained for various Pb-containing crystalline compounds and high lead glasses. The isotropic chemical shifts were determined for the crystalline samples. The more ionic lead atoms with a coordination number larger than six had relatively small chemical shifts between 0 and 2382 ppm with respect to crystalline Pb(NO₃)₂. On the other hand, the covalent lead atoms with PbO₃ trigonal and PbO₄ square pyramidal configurations gave a multiplet line profile with shifts ranging from about 3000 to 6000 ppm. The lead atoms with different local environments in PbSiO₃ (alamosite) and H-Pb₂SiO₄, for instance, could be clearly distinguished from each other on the basis of the isotropic chemical shift. The NMR spectra for the high lead glasses of composition 67PbO·33SiO₂, 80PbO·20B₂O₃ and 70PbO· 30GaO_1.5 were found to exhibit an extremely broad peak with a shift ranging from about 3000 to 6000 ppm. This shift indicates that, in these glasses, neither such highly ionic lead atoms as found in symmetrical PbO₆ octahedra nor such highly covalent ones as found in PbO₄ square pyramids in the PbO crystal are predominant, but instead PbO₃ trigonal or PbO₄ square pyramids, with two or three other neighboring oxygens at larger distances as found in H-Pb₂SiO₄ or PbSiO₃, are the major lead-oxygen configuration.     

Heat capacity of CeIrSi3 under pressure

We measured the heat capacity of CeIrSi₃ (100 mK<T<6 K) under high pressure up to P=1.38 GPa. The measurements have been used a quasiadiabatic method utilizing a CuBe piston-cylinder pressure cell in a dilution refrigerator. At 0 GPa, a sharp anomaly which indicates the antiferromagnetically transition is observed at T_N=5 K. T_N decreases monotonically with increasing pressure up to P=1.38 GPa. The magnetic entropy is released below T_N only 19% of R ln 2 at 0 GPa. And the magnetic entropy decreases with increasing pressure up to 1.38 GPa, 64% compared to that at 0 GPa.     

Constituents of holothuroidea, 14. Isolation and structure of new glucocerebroside molecular species from the sea cucumber Stichopus japonicus

Five glucocerebroside molecular species, SJC-1-SJC-5, have been isolated from the less polar lipid fraction of a chloroform/methanol extract of the sea cucumber Stichopus japonicus. The structures of these glucocerebroside molecular species were determined on the basis of chemical and spectroscopic evidence. SJC-1, SJC-2, and SJC-3 are typical sphingosine- and phytosphingosine-type glucocerebroside molecular species with nonhydroxylated and hydroxylated fatty acyl moieties. SJC-4 and SJC-5 are also sphingosine-type glucocerebroside molecular species with hydroxylated fatty acyl moieties, although they are new glucocerebroside molecular species with unique sphingosine bases.     

Effect of a thin dielectric layer on terahertz transmission characteristics for metal hole arrays

We studied the role of surface-plasmon polaritons (SPPs) in a bandpass transmission property of two-dimensional metal hole arrays (2D-MHAs) by investigating the effect of thin dielectric layers on the 2D-MHA surfaces. We measured zero-order transmission spectra of the 2D-MHAs by changing the thickness of the dielectric layer and found that the bandpass transmission peak shifted to the lower-frequency side with increasing layer thickness, owing to the change of the resonant frequency of the SPP. This result shows that SPPs play a crucial role in the transmission property of 2D-MHAs in the terahertz region.     

Interpolation inequalities in Besov spaces

In this paper we present an interpolation inequality in the homogeneous Besov spaces on , which reduces to a number of well-known inequalities in special cases.

     

On the property of eigenvalues of some infinitesimal generator

We analyze a class of finite dimensional birth-and-death processes. New conclusions are reached for the property of the eigenvalues of the infinitesimal generator for these processes.     

Focusing effect measurements of artificial dielectric multilayer lens with metal rectangular chips for terahertz wave band

This paper presents the design and fabrication of an artificial multilayer lens comprising ten layers of metal rectangular chips on a cyclo olefin polymer, which has low loss in the terahertz band. Measurements of the focusing effect are also presented. The focusing effect is produced by the rectangular metallic chips which act as an electrical dipole. Simulations are performed using ANSYS HFSS. The lenses are fabricated by laser processing or semiconductor etching. The focusing effect is confirmed by measurement using terahertz near-field microscopy, although some discrepancies are observed between the simulated and measured results.     

Total syntheses of (+)-polygalolide a and (+)-polygalolide b: elucidation of the absolute stereochemistry and biogenetic implications

The total syntheses of (+)-polygalolide?A and (+)-polygalolide?B have been completed by using a carbonyl ylide cycloaddition strategy. Three of the four stereocenters, including two consecutive tetrasubstituted carbon atoms at C2 and C8, were incorporated through internal asymmetric induction from the stereocenter at C7 by a [Rh(2) (OAc)(4)]-catalyzed carbonyl ylide formation/intramolecular 1,3-dipolar cycloaddition sequence. The arylmethylidene moiety of these natural products was successfully installed by a Mukaiyama aldol-type reaction of a silyl enol ether with a dimethyl acetal, followed by elimination under basic conditions. We have also developed an alternative approach to the carbonyl ylide precursor based on a hetero-Michael reaction. This approach requires 18 steps, and the natural products were obtained in 9.8 and 9.3?% overall yields. Comparison of specific rotations of the synthetic materials and natural products suggests that polygalolides are biosynthesized in nearly racemic forms through a [5+2] cycloaddition between a fructose-derived oxypyrylium zwitterion with an isoprene derivative.