Application of Chromium-Arene Complexes in the Organic Synthesis. Efficient Synthesis of Stilbene Phytoalexins

Planar chiral ⁶-arene-Cr(CO)₃ complexes represent highly valuable building blocks for the diastereo- and enantioselective synthesis. Their employment as synthons offer new and unique opportunities for the stereoselective multistep synthesis of complex natural products. The strategy of novel efficient synthesis of stilbene phytoalexins was based on arene chromium chemistry and the chemical and stereochemical effects of the metal unit on the reactivity of complexed arene ligand and stereochemical features of such compounds. Two variants for the construction of the trans-stilbene and diarylethanol framework via facilitated benzylic deprotonation of an ⁶-benzene-Cr(CO)₃ complex and subsequent coupling with para-anisaldehyde in an aldol-type or a Wittig–Horner reaction were suggested.     

Electroviscous Forces on a Charged Cylinder Moving Near a Charged Wall

The refined theory of the electroviscous lift forces is presented for the case when the separation distance between the particle and the wall is larger than the double-layer thickness. The theory is based on the lubrication approximation for motion of a long cylinder near a solid wall in creeping flow. The approximate analytical formula for the lift force valid for Pe相似文献   

Synthesis and selective silylation of ω-hydroxy functionalized (η-alkenyl)carbene complexes of chromium(0) and tungsten(0) Part 11. The chemistry of metallacyclic alkenylcarbene complexes

Tungsten(0) carbene complexes of the type (OC)₅WC(NMeCH₂CHCHCH₂OH)R 2 (R=Me: 2a; R=Ph: 2b) were generated by aminolysis of (OC)₅WC(OMe)R with cis-NHMeCH₂CHCHCH₂OH. Like their Cr-congeners 1, complexes 2 exist at room temperature as mixtures of Z- and E-isomers with regard to the C-N bond. The metallacyclic complexes (OC)₄WC(η²-NMeCH₂CHCHCH₂OH)R (4) were obtained in good yields upon photo-decarbonylation of 2. Deprotonation/silylation of the complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)Me (M=Cr: 3a; M=W: 4a) with one equivalent of ⁿBuLi/Me₃SiCl gave (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₃ (M=Cr: 5; M=W: 6), whereas with two equivalents of ⁿBuLi/Me₃SiCl complexes (OC)₄MC(η²-NMeCH₂CHCHCH₂OSiMe₃)CH₂SiMe₃ (M=Cr: 7; M=W: 8) were formed. Hydrolysis of the latter yielded selectively (OC)₄MC(η²-NMeCH₂CHCHCH₂OH)CH₂SiMe₃ (M=Cr: 9; M=W: 10). The complexes 1-10 were analyzed in solution by one- and two-dimensional NMR spectroscopy (¹H, ¹³C, ²⁹Si, ¹H/¹H COSY, ¹H/¹H NOESY, ¹³C/¹H HETCOR).     

Beitrag zur Isomerenanalyse des Kautschuks

Zusammenfassung Die beiden 1,4-Isomeren des Polyisoprens wurden bisher infrarotspektroskopisch an Hand der Banden bei 840,1100 und 4050 cm^–1 ermittelt. Da die betreffenden Verfahren gegenüber Störungen empfindlich sind, ist es günstiger, wenn die Bestimmungen mit Hilfe von Bandenverhältnissen erfolgen. An der Bandengruppe bei 1100 cm^–1 lassen sich mehrere derartige Verhältnisse bilden, die — unempfindlich gegenüber Untergrundstörungen — auf optisch aktive Verunreinigungen verschieden reagieren.Für die Bestimmung der Extinktionskoeffizienten der 1,2- und der 3,4-Struktur wird ein Verfahren angegeben, bei dem unter Einschaltung der Benzopersäuremethode die Eichwerte direkt an Kautschukproben gewonnen werden können.Bei routinemäßigen Analysen bestimmt man das Verhältnis der beiden 1,4-Isomeren an den Banden bei 1100 cm^–1, während die Gesamtkonzentration dieser beiden Komponenten mit Hilfe der Summenbande bei 840 cm^–1 ermittelt wird. Die Teilkonzentrationen der anderen beiden Komponenten werden ebenfalls aus dem Spektrum berechnet und die prozentualen Anteile durch Bildung der entsprechenden Verhältnisse ermittelt. Da auf diese Weise eine experimentelle Konzentrationsbestimmung nicht nötig ist, können nach dem Verfahren auch unlösliche Isoprenpolymerisate im angequollenen Zustand analysiert werden.Die Arbeit wurde im Untersuchungslaboratorium des VEB Chemische Werke Buna (Schkopau Kr. Merseburg) durchgeführt. Für die Unterstützung und das der Arbeit entgegengebrachte Interesse danken wir an dieser Stelle Herrn Prof. Dr. Dr. h. c. J. Nelles sowie den Herren Dr. A. Grimm und Dr. W. Luchsinger. Weiterhin möchten wir Frl. B. Randzio, Frl. L. Russ, Frau Chr. Scholz und Herrn M. Röder für die zahlreichen Untersuchungen unseren Dank aussprechen.Teil I: Schmalz, E. O., u. G. Geiseler: diese Z. 190, 293 (1962).Teil der Dissertation, Universität Leipzig 1961.     

The zero curvature equation for rigid CR-manifolds

In this paper, we present the general analytic solution to the zero curvature equation for rigid three-dimensional CR-manifolds. The solutions are uniquely determined by one function and four real parameters.     

Nucleoside Analogues with a 1,3‐Diene?Fe(CO)3 Substructure: Stereoselective Synthesis,Configurational Assignment,and Apoptosis‐Inducing Activity

The synthesis and stereochemical assignment of two classes of iron‐containing nucleoside analogues, both of which contain a butadiene? Fe(CO)₃ substructure, is described. The first type of compounds are Fe(CO)₃‐complexed 3′‐alkenyl‐2′,3′‐dideoxy‐2′,3′‐dehydro nucleosides (2,5‐dihydrofuran derivatives), from which the second class of compounds is derived by formal replacement of the ring oxygen atom by a CH₂ group (carbocyclic nucleoside analogues). These compounds were prepared in a stereoselective manner through the metal‐assisted introduction of the nucleobase. Whilst the furanoid intermediates were prepared from carbohydrates (such as methyl‐glucopyranoside), the carbocyclic compounds were obtained by using an intramolecular Pauson–Khand reaction. Stereochemical assignments based on NMR and CD spectroscopy were confirmed by X‐ray structural analysis. Biological investigations revealed that several of the complexes exhibited pronounced apoptosis‐inducing properties (through an unusual caspase 3‐independent but ROS‐dependent pathway). Furthermore, some structure–activity relationships were identified, also as a precondition for the design and synthesis of fluorescent and biotin‐labeled conjugates.