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51.
Oxorhenium(V) complexes [ReOX3(PPh3)2] (X = Cl, Br) react with phenylacetylene under formation of complexes with ylide‐type ligands. Compounds of the compositions [ReOCl3(PPh3){C(Ph)C(H)(PPh3)}] ( 1 ), [ReOBr3(OPPh3){C(Ph)C(H)(PPh3)}] ( 2 ), and [ReOBr3(OPPh3){C(H)C(Ph)(PPh3)}] ( 3 ) were isolated and characterized by X‐ray diffraction. They contain a ligand, which was formed by a nucleophilic attack of released PPh3 at coordinated phenylacetylene. The structures of the products show that there is no preferable position for this attack. Cleavage of the Re–C bond in 3 and dimerization of the organic ligand resulted in the formation of the [{(PPh3)(H)CC(Ph)}2]2+ cation, which crystallized as its [(ReOBr4)(OReO3)]2– salt. 相似文献
52.
53.
Ying Han 《Tetrahedron》2010,66(39):7743-7748
New zwitterionic salts of pyridinium-Meldrum acid and pyridinium-barbituric acid are conveniently synthesized from the three-component reactions of 2-, 3-, or 4-pyridacylpyridinum iodides, aromatic aldehydes, and Meldrum acid or N,N-dimethylbarbituric acid in the presence of triethylamine as base promoter in acetonitrile. 相似文献
54.
Ramazan Erenler 《Tetrahedron letters》2005,46(34):5683-5685
The conversion of 4-pyridyl propargylic alcohols 1 to the (E)-propenones 3 and propynones 2 occurs under mild reaction conditions, pyridinium chloride in methanol at room temperature. (Z)-4-Pyridyl propenones 11 are detected as initial products when large substituents such as trimethylsilyl, tert-butyl and phenyl are attached at C-3 of the propynols and these (Z)-enones 11 are isomerised to the (E)-isomers 3 under the reaction conditions. In the presence of deuterated solvent, both hydrogens at the double bond of enone 3d are deuterated. An allenol is proposed as intermediate whose preferential protonation occurs at the less hindered side giving the (Z)-enone. The propargylic alcohols, pyridin-2-yl 12 and quinolin-4-yl 5, are converted to (E)-enones 13 and 7, respectively. 相似文献
55.
The reactions of several thioketones containing a conjugated C?C bond with diazo compounds were investigated. All of the selected compounds reacted via a 1,3‐dipolar cycloaddition with the C?S group and subsequent N2 elimination to yield thiocarbonyl ylides as intermediates, which underwent a 1,3‐dipolar electrocyclization to give the corresponding thiirane 25 , or, by a subsequent desulfurization, to give the olefins 33a and 33b . None of the intermediate thiocarbonyl ylides reacted via 1,5‐dipolar electrocyclization. If the α,β‐unsaturated thiocarbonyl compound bears an amino group in the β‐position, the reactions with diazo compounds led to the 2,5‐dihydrothiophenes 40a – 40d . In these cases, the proposed mechanism of the reactions led once more to the thiocarbonyl ylides 36 and thiiranes 38 , respectively. The thiiranes reacted via an SNi′‐like mechanism to give the corresponding thiolate/ammonium zwitterion 39 , which underwent a ring closure to yield the 2,5‐dihydrothiophenes 40 . Also in these cases, no 1,5‐dipolar electrocyclization could be observed. The structures of several key products were established by X‐ray crystallography. 相似文献
56.
Norbert W. Mitzel Daniel H. Brown Simon Parsons Paul T. Brain Colin R. Pulham David W. H. Rankin 《Angewandte Chemie (International ed. in English)》1998,37(12):1670-1672
Clearly different from local C 3 symmetric is the heavy-atom core of Me3P=CH2, the simplest phosphonium ylide. The geometry obtained by reanalysis of gas-electron-diffraction data from 1977 is now consistent with theoretical calculations, but different from the molecular structure in the solid state. The picture shows the structure of Me3P=CH2 in the gas phase (a) and in the crystal (c) together with the calculated transition state (b) (viewed along the P=C bond). 相似文献
57.
Dimeric Dialkylphosphanylgermylenes: Ylidic Diphosphadigermetanes The dichlorogermylene triphenylphosphane complex ( 1 ) reacts with di-t-butyl(trimethylsilyl)phosphane ( 2 a ) only in a 1 : 1 stoichiometry providing dimeric chloro(di-t-butylphosphanyl)germylene ( 3 a ); with two equivalents of diisopropyl(trimethylsilyl)phosphane ( 2 b ), however, 1 (or the dichlorogermylene dioxane complex) provide straightforwardly dimeric bis(diisopropylphosphanyl)germylene ( 5 b ) as yellow crystals. The trans-dimeric structures of 3 a and 5 b are confirmed by spectroscopic data and by X-ray diffraction. Dialkylphosphanylgermylenes 3 a and 5 b are ylide-type diphosphadigermetanes in solution and in the solid state. 相似文献
58.
Raj K. Bansal Neelima Gupta K. Karaghiosoff P. Mayer M. Vogt 《Tetrahedron letters》2004,45(41):7771-7773
An X-ray crystal structure investigation as well as theoretical DFT (hybrid B3LYP/6-31G** level) calculations of 2-ethylpyridinium dichlorophosphino-ethoxycarbonylmethylide confirm the existence of significant n→σ* negative (anionic) hyperconjugation between the ylidic charge and the σ*P-Cl bond in the most stable conformer, which has the phosphorus lone pair oriented orthogonally to the ylidic pz orbital, resulting in elongation of the P-Cl bond parallel to the pz orbital but shortening of the C-P bond. 相似文献
59.
Premchendar Nandhikonda 《Tetrahedron》2009,65(11):2173-2177
As a minimum modification approach toward longer wavelength chromophores, a series of (4-diethylamino-1,8-naphthaloyl)-aminopyridines were prepared with the pyridine nitrogen located at the ortho, meta, and para positions. Comparison between these isomeric neutral dyes and their corresponding pyridinium-1,3-propanesulfonate salts reveals a red-shift in both absorption (up to an emission of 1682 cm−1 in ethyl acetate) and emission. These observed shifts along with increased fluorescence quantum yield are attributed to polarization induced by the quaternary nitrogen of the pyridinium cation. 相似文献
60.
Hubert Schmidbaur 《Angewandte Chemie (International ed. in English)》1983,22(12):907-927
Phosphorus ylides are not only classical reagents in organic chemistry, but also play an increasingly important role as novel components in organometallic compounds. These metallic “ylide complexes” are either synthesized from “preformed ylides” and coordination compounds by addition or substitution, on the building block principle, or they are formed, in sometimes complicated reactions, from phosphanes, metal complexes, and C1 substrates in the coordination sphere of the metals. The resulting metal-carbon bonds are greatly modified in their properties by the immediate presence of the phosphonium center and often belong to the most stable of M-C structural units. The metal can come from any group of the periodic table, including the lanthanoids and actinoids. Numerous preparative and structural studies are gradually enabling us to gain an overall picture of the scope of this area of research. 相似文献