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991.
The structures of two carbonylphosphine complexes of chromium were determined by X-ray analysis. cis-Tricarbonyltriphosphinechromium(0), [(CO)3(PH3)3Cr], crystallizes in space group P21/m with a = 6.90± 0.01, b = 11.29±0.02, c = 6.41±0.01 Å, β = 93.80±0.08°, Z=2. The structure was solved by conventional methods and refined by least squares (R1 = 0.056). The idealized octahedral molecule shows approximate C3v, symmetry. The mean CrP-distance is 2.346±40.003 Å. Pentacarbonylphosphinechromium, [(CO)5(PH3)Cr], crystallizes in spacegroup Pnma with a = 12.23±0.02, b = 11.33±0.02, c = 6.61 ±0.01 Å, Z = 4. Cell dimensions and structural parameters are very similar to those of hexacarbonylchromium(0). In the crystal the PH3 group is disordered over three mutually cis-positions of the coordination octahedron.  相似文献   
992.
Quinazoline Carboxylic Acids. An Easy Route to (4-Oxo-3,4-dihydroquinazolin-3-yl)-alkanoic Acids, (4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)-alkanoic Acids and their Esters A new route was found for the synthesis of (4-Oxo-3,4-dihydroquinazolin-3-yl)-alkanoic acids ( 8 ) and (4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)-alkanoic acids ( 6 ) by cyclization of the N-(2-aminobenzoyl)amino acids 5 with HCOOH or HNO2. 2H-3,1-Benzoxazine-2,4(1H)-diones ( 1 ) reacted with glycine esters to 2 , which were cyclized by HNO2 to the esters 4 . Ester 4 was hydrolyzed to 6 (X = CH2). Diones 1 reacted with the most common amino acids (as the ammonium salt of tertiary amine) to amino-alkanoic acids 5 , which were cyclized with orthoformate to 7 or 8 depending on the reaction conditions.  相似文献   
993.
A novel ruthenium-catalyzed ring opening/ring closing tandem metathesis reaction with a catalytic transfer of stereocenters from a ring to an olefinic chain is described. This ring rearrangement serves as the key step in the stereoselective synthesis of the new azasugar analogues 1 and 2.  相似文献   
994.
Intermittency effects in high Reynolds number turbulence (Re103–106) are calculated from the Navier-Stokes equation in Fourier-Weierstrass approximation. First, the probability density functions (PDF) of scale resolved turbulent signals is found to be Gaussian for large scales, whereas for smaller scales the PDF changes (in agreement with experiment) to a more and more stretched exponential type. This is due to intermittent small scale fluctuations which are caused by the competition between turbulent energy transfer downscale and viscous energy loss. Second, we calculate the moments of ther-averaged energy dissipation rate r (x) and theirr-scaling exponents (m/3). Our results well agree with experiment and numerical simulations of the full Navier-Stokes equations ((2)=0.29±0.02). We analytically show that the common identification between the (m/3) and the corrections (m) to classical scaling of the velocity structure functions (Kolmogorov's refined similarity hypothesis) is doubtful, because even Gaussian 1 u 1-PDFs (characterizing non intermittent flow) lead to (m/3)0.  相似文献   
995.
Summary Reactions of -chloro--cyano--(5-nitrofur-2-yl)-acrylic acid derivatives with malonic acid derivatives in the presence of collidine yield the allyl anions3a–d. The pyridines4, 8 or9 are formed by cyclization of3 under acidic conditions. The 2-chloropyridine4a reacts with nucleophiles under substitution. The treatment of ethyl dichloropropionate1b with C-H-acidic compounds provided the cyclopropanes11 or12, the configurations of which were determined by13C-NMR spectroscopy. The results of the X-ray structure analysis of8c are discussed.
Furylvinylhalogenide, 12. Mitt.: Reaktionen von -Chlor--(5-nitrofur-2-yl)--cyanacrylsäurederivaten mit Malonsäurederivaten
Zusammenfassung Die Umsetzung von -Chlor--cyan--(5-nitrofur-2-yl)-acrylsäurederivaten mit Malonsäurederivaten in Gegenwart von Collidin führt zu Allylanionen3a–d. Unter sauren Bedingungen cyclisiert3 zu den Pyridinen4, 8 oder9. Das 2-Chlorpyridin4a reagiert mit Nukleophilen unter Substitution. Setzt man den Dichlorpropionsäureester1b mit C-H-aciden Verbindungen in Gegenwart von Collidin um, so werden die Cyclopropane11 bzw.12 gebildet, deren Konfigurationen mit Hilfe der13C-NMR-Spektroskopie bestimmt wurden. Die Ergebnisse der Röntgenkristallstrukturanalyse von8c werden diskutiert.
  相似文献   
996.
LetX 1,X 2,... be i.i.d. random variables with values in a simply connected nilpotent Lie groupG. Assume the laws of to be weakly convergent to a probability measure onG, n Aut(G), and (k n)n strictly increasing in. In this paper we want to characterize the possible limit laws. We obtain that every limit law is continuously embeddable and we prove a kind of functional limit theorem. Further, we study the connections between two different concepts of stability (resp. semistability) and limit laws. Finally, we describe the various domains of attraction of measures (resp. of convolution semigroups).  相似文献   
997.
998.
The biosynthesis of thebaine is based on the regioselective, intramolecular, oxidative coupling of (R)‐reticuline. For decades, chemists have sought to mimic this coupling by using stoichiometric oxidants. However, all approaches to date have suffered from low yields or the formation of undesired regioisomers. Electrochemistry would represent a sustainable alternative in this respect but all attempts to accomplish an electrochemical synthesis of thebaine have failed so far. Herein, a regio‐ and diastereoselective anodic coupling of 3′,4′,5′‐trioxygenated laudanosine derivatives is presented, which finally enables electrochemical access to (?)‐thebaine.  相似文献   
999.
A novel strategy for the synthesis of biaryls consisting of a benzothiophene and a phenol moiety is reported. These heterobiaryls are of utmost interest for pharmaceutical, biological, and high‐performance optoelectronic applications. The metal‐ and reagent‐free, electrosynthetic, and highly efficient method enables the generation of 2‐ and 3‐(hydroxyphenyl)benzo[b]thiophenes in a regioselective fashion. The described one‐step synthesis is easy to conduct, scalable, and inherently safe. The products are afforded in high yields of up to 88 % and with exquisite selectivity. The reaction also features a broad scope and tolerates a large variety of functional groups.  相似文献   
1000.
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