排序方式: 共有45条查询结果,搜索用时 15 毫秒
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Pei-Hsun Wei Mukulesh Mondal Gero D. Harzmann Kraig A. Wheeler 《Tetrahedron letters》2010,51(51):6690-6694
The mechanism of PBu3-catalyzed homodimerization of ketoketenes has been explored and compared with that of the previously reported trialkylphosphite-mediated reactions. NMR studies of the PBu3-catalyzed reaction implicated the involvement of tetravalent phosphonium intermediates. Phosphonium intermediates in the catalytic cycle were trapped through reaction with trimethylsilyl chloride and 4-chlorobenzaldehyde, and the resulting products were characterized. A method for the stoichiometric generation of phosphonium enolates was developed as a result of these studies. No evidence was obtained for the involvement of pentacovalent phosphorane intermediates in trialkylphosphine-catalyzed ketoketene homodimerization reactions, in contrast with the mechanism of the trialkylphosphite-mediated homodimerization of dimethylketene. An X-ray crystal structure analysis of methylphenylketene dimer showed that it possesses Z-geometry about the exocyclic olefin. 相似文献
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Max M. Abrahams Gregory W. Cushing Zachary N. Pickett William A. Howard Kraig A. Wheeler 《Journal of chemical crystallography》2010,40(7):583-590
Abstract
Mer-RhBr3(Me2pzH)3 (Me2pzH = 3,5-dimethylpyrazole) (monoclinic, P21/n, a = 8.3300 (5) Å, b = 16.2889 (9) Å, c = 15.9299 (11) Å, α = 90°, β = 100.217 (5)°, γ = 90°; V = 2,127.2 (2) Å3; Z = 4) has been characterized by X-ray diffraction, 1H and 13C nuclear magnetic resonance spectroscopy, infrared spectroscopy, and electronic absorption spectroscopy, and modeled by density functional theory (DFT) and time-dependent density functional theory (TDDFT). Mer-RhBr3(Me2pzH)3 is an octahedral complex with a HOMO → LUMO transition at 486 nm. The DFT and TDDFT calculations predicted mer-RhBr3(Me2pzH)3 to be an octahedral complex with a HOMO → LUMO transition at 540 nm. 相似文献3.
A palladium-catalyzed multicomponent synthesis of imidazolinium carboxylates and imidazolines is described. The palladium catalyst [Pd(CH(R(1))N(R(2))COR(3))Cl](2), or [Pd(allyl)Cl](2), with P(t-Bu)(2)(2-biphenyl) can mediate the simultaneous coupling of two imines, acid chloride, and carbon monoxide into substituted imidazolinium carboxylates within hours under mild conditions (45 °C, 4 atm of CO). The reaction proceeds in good yield with aryl-, heteroaryl-, and alkyl-substituted acid chlorides, as well as variously functionalized imines. Imidazolines are formed via the initial generation of Mu?nchnone intermediates, followed by their cycloaddition with an in situ generated protonated imine. The addition of an amine base can intercept catalysis at Münchnone formation, which allows the subsequent cycloaddition of a second imine. The latter provides a route for the assembly of complex, polysubstituted imidazolinium carboxylates with independent control of all five substituents. The subsequent removal of the nitrogen substituent(s) provides an overall synthesis of imidazolines. 相似文献
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Mateusz F. Serafin Kraig A. Wheeler 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):o620-o621
The title bimolecular compound, C4H5N3·C21H18O2, constructed from 2‐aminopyrimidine and 3,3,3‐triphenylpropanoic acid, forms a tetramolecular hydrogen‐bonded motif via O—H...N, N—H...O and N—H...N contacts. This aggregate organizes to give crystal‐packing motifs with hydrophilic and hydrophobic regions. 相似文献
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George D. Bennett Lauren R. Bringman Elise M. Wildman Kraig A. Wheeler 《Journal of chemical crystallography》2010,40(1):76-79
Abstract
The title compounds, C10H12O4 and C12H14O5, were prepared as part of an ongoing study to explore the practical aspects of solventless reaction methods. As confirmed by the crystal structures, treatment of maleic anhydride with (2E,4E)-hexa-2,4-dien-1-ol or its acetate counterpart resulted in cis bicyclo [4.3.0] molecular frameworks. The racemic product derived from the dienol synthon crystallized in chiral space group P212121 via a pasteurian resolution process with molecules organized by carboxyl⋯carboxyl and C–H⋯O contacts. The acetate derivative crystallizes in space group Cc. 相似文献9.
Kraig A. Wheeler 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(5):o231-o233
The title trans prolyl amide exists as a benzene solvate, C15H18N2O3·C6H6, with positional disorder of the prolyl ring. The molecular structure is influenced by a close intramolecular N—H⋯N contact that provides structural support for the intramolecular catalysis of peptidyl–prolyl cis–trans isomerization. 相似文献
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Thomas J. Otto Kraig A. Wheeler 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):704-705
The title compound, poly[[aquazinc(II)]‐μ‐benzene‐1,3‐dicarboxylato‐O1:O1′:O2], [Zn(C8H4O4)(H2O)]n, forms a metal–organic coordination network that consists of tetrahedral Zn atoms bonded to one water molecule and three carboxylate groups. Isophthalate groups bridge the four‐coordinate Zn centers to generate two‐dimensional architectures in the ac plane. These planar zinc isophthalate motifs are linked by infinite C=O?H—O—H interactions along the a axis to form a chiral framework. The observed polar structural pattern originates due to the distorted tetrahedral Zn centers [O—Zn—O 100.7 (2)–136.0 (1)°] and the alignment of the water molecules. Bridging isophthalate groups align to form approximate centrosymmetric motifs. 相似文献