The first stereoselective total synthesis of gamahonolide A (1) has been accomplished using aminoxylation, Keck allylation, and ring-closing metathesis (RCM) reactions as key steps. 相似文献
We describe the synthesis, crystal structures, and optical absorption spectra/colors of 3d‐transition‐metal‐substituted α‐LiZnBO3 derivatives: α‐LiZn1?xMIIxBO3 (MII=CoII (0<x<0.50), NiII (0<x≤0.05), CuII (0<x≤0.10)) and α‐Li1+xZn1?2xMIIIxBO3 (MIII=MnIII (0<x≤0.10), FeIII (0<x≤0.25)). The crystal structure of the host α‐LiZnBO3, which is both disordered and distorted with respect to Li and Zn occupancies and coordination geometries, is largely retained in the derivatives, which gives rise to unique colors (blue for CoII, magenta for NiII, violet for CuII) that could be of significance for the development of new, inexpensive, and environmentally friendly pigment materials, particularly in the case of the blue pigments. Accordingly, this work identifies distorted tetrahedral MO4 (M=Co, Ni, Cu) structural units, with a long M?O bond that results in trigonal bipyramidal geometry, as new chromophores for blue, magenta, and violet colors in a α‐LiZnBO3 host. From the L*a*b* color coordinates, we found that Co‐substituted compounds have an intense blue color that is stronger than that of CoAl2O4 and YIn0.90Mn0.10O3. The near‐infrared (NIR) reflectance spectral studies indicate that these compounds exhibit a moderate IR reflectivity that could be significant for applications as “cool pigments”. 相似文献
The gas-phase coordination behavior of the [Cr(III)(Salen)]PF(6) complex at the free axial positions has been studied in the presence of amines as ligands (propylamine and a series of diamines) under electrospray ionization conditions. The [Cr(III)(Salen)](+) complex formed stable five- and six-coordinated complex ions, [Cr(III)(Salen)(L)](+) and [Cr(III)(Salen)(L)(2)](+), respectively, where L = solvent molecule or amine. When diamines were used as ligands, abundant [Cr(III)(Salen)(L)](+) ions were observed in which two axial positions of the [Cr(III)(Salen)](+) species are occupied by the two amino groups of the diamine ligand. The relative abundances of ligated complex ions, fragment ions, and solvent adducts of fragment ions in the ESI mass spectra, were found to depend on the cone voltage used to record the spectrum. The ESI mass spectra of [Cr(III)(Salen)](+) in the presence of diamines as ligands, and experiments on ligand-pickup in the collision cell, clearly demonstrated that the [Cr(III)(Salen)(L)](+) complex ion is stable for 1,2-diaminoethane and 1,3-diaminopropane. The stability of [Cr(III)(Salen)(L)](+) ions gradually decreased from 1,4-diaminobutane to 1,6-diaminohexane, and then showed a slight increase for 1,7-diaminoheptane and 1,8-diaminooctane. The collision-induced dissociation spectra of [Cr(III)(Salen)(L)](+) ions support the above observations. 相似文献
In this work a number of techniques (electronic speckle pattern interferometry, holographic interferometry, strain gauge and finite element method) are brought to bear in order to establish consistency in the results of strain measurement. This is necessary if optical non-destructive testing methods, such as those used here, are to gain acceptance for routine industrial use. The FE model provides a useful check. Furthermore, ESPI fringe data facilitates the extension of FE models, an approach that is of growing importance in component testing.
The use of in-plane and out-of-plane sensitive electronic speckle pattern interferometry (ESPI) for non-destructive material characterization of thick unplasticised polyvinylchloride (uPVC) pipes is presented. A test rig has been designed for stressing pipes by internal pressure. ESPI gives a complete mapping of the displacement field over the area imaged by the video camera. The results for the strain of uPVC obtained from ESPI data and from strain gauges are in good agreement. The value of Young's modulus has been obtained from the fringe data and compared with results obtained using holographic interferometry and from strain gauge measurements. The FE model also produces fringe data that is consistent with the ESPI results. 相似文献
A number of complexes of Co(II), Ni(II), Cu(II), Ru(II), Pd(II) and Pt(II) with 2-methyl-3-(carboxy methyl) quinazolin (3H)-4-one
(MCMQ) and 2-phenyl-3-(carboxy methyl) quinazolin (3H)-4-one (PCMQ) have been synthesized and characterized by analytical,
conductivity, thermal, magnetic, infrared, electronic, proton magnetic resonance and electron spin resonance spectral data.
Based on analytical data, the stoichiometry and the association with other molecules of the complexes have been determined.
Conductivity data show that all these complexes are nonelectrolytes. Infrared and PMR spectral data indicate that both the
ligands are uninegative bidentate with all the metal ions. Based on electronic spectral data, the geometries of the complexes
have been indicated. Electronic spectral parameters for Co(II) and Ni(II) and ESR parameters for Cu(II) complexes have been
calculated and relevant conclusions have been drawn with respect to the nature of bonds present in them. 相似文献
The synthesis of the styryl lactone Leiocarpin C has been achieved in a highly stereoselective manner using Jacobsen’s kinetic resolution, Sharpless asymmetric epoxidation and Sharpless asymmetric dihydroxylation as key steps. This is the first total synthesis of Leiocarpin C, and thus establishes for the first time the absolute stereochemistry of this natural product. 相似文献