Applications of vinylogous Mannich reactions. Total syntheses of the Ergot alkaloids rugulovasines A and B and setoclavine.

Concise syntheses of the Ergot alkaloids rugulovasine A (3a), rugulovasine B (3b), and setoclavine (2) have been completed by strategies that feature inter- and intramolecular vinylogous Mannich reactions as the key steps. Thus, the first synthesis of 3a,b commenced with the conversion of the known indole 17 into 24 via the addition of the furan 22 to the iminium ion 21, which was generated in situ from the aldehyde 19. Cyclization of 24 by a novel S(RN)1 reaction followed by removal of the N-benzyl group furnished a mixture (1:2) of 3a and 3b. In an alternative approach to these alkaloids, the biaryl 35 was reduced with DIBAL-H to give an intermediate imine that underwent spontaneous cyclization via an intramolecular vinylogous Mannich addition to provide 36a,b. N-Methylation of the derived benzyl carbamates 37a,b followed by global deprotection gave a mixture (2:1) of rugulovasines A and B (3a,b). Setoclavine (2) was then prepared from the biaryl 41 using a closely related intramolecular vinylogous Mannich reaction to furnish the spirocyclic lactones 42a,b. These lactones were subsequently transformed by hydride reduction and reductive methylation into the ergoline derivatives 43a,b, which were in turn converted into 2 by deprotection and solvolytic 1,3-rearrangement of the allylic hydroxyl group.     

Extremal Set Systems with Weakly Restricted Intersections

Received: March 17, 1997?Revised: November 16, 1998     

Spectrum of signals

Finite-energy high frequency signals, band-pass frequency signals, and band-stop frequency signals are characterized.     

Harmonic polynomials and their application in solving problems of the mathematical theory of cracks

We consider new spectral relations for harmonic polynomials of two variables. The basic relations of this type are the integral relations in a disk, which make it possible to use these polynomials to construct the solution of certain singular equations of Newtonian potential type, of both first and second kind, given on the disk. By use of these results we determine the eigenvalues of certain two-dimensional integral equations of second kind.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 36, 1992, pp. 88–93.     

Neue Verfahren für die elektroanalytische Bestimmung von Hydroxylamin. I. Niederschlagsmethoden

Zusammenfassung Wir konnten zeigen, daß die Fällungstitration für die Bestimmung von reinem Hydroxylamin-hydrochlorid und -sulfat mit Erfolg angewandt werden kann. Zur Ermittlung des Endpunktes wurden verschiedene elektrometrische Methoden angewandt. Die Resultate stehen untereinander in guter Übereinstimmung und entsprechen den berechneten Werten.

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New procedures for the determination of hydroxylammonium salts applying electroanalytical methods. I

Summary As our investigations show it was possible to determine pure chloride and sulfate of hydroxylamine by means of precipitation titrations. Various electrometric methods for the end-point detection were applied, among them our biamperometric method with polarised bismuth electrode pair. These different methods gave expected and mutually well agreed results.

     

Biexciton two-photon absorption in CuBr

The biexciton states in CuBr have been studied at K ? 0 by two-photon absorption, using two different laser sources. The energy and the symmetry of these states have been unambiguously assigned: E_B(Γ₁) = 5.9061 eV, E_B(Γ₅) = 5.9103 eV, E_B(Γ₃) = 5.9128 eV.     

Processus simultane d'évaporation libre et de diffusion de surface

If a conical metal tip is annealed in vacuum, the radius at the apex increases with time by surface diffusion. This was calculated by Nichols and Mullins and recently verified by the authors. This phenomenon is now calculated in case of a simultaneous action of evaporation and surface diffusion. By evaporation the blunting rate should be lowered until it becomes zero for a critical value of the curvature radius. Numerical data for different temperatures and cone angles are calculated for some metals (W, Mo, Pt, Ni, Cu). Measured are profile changes of Mo tips during annealing. The lowering of the blunting rate and the existence of a limit radius are confirmed. An evaporation can also occur as a consequence of a surface reaction. The measured radius changes of tungsten tips annealled in 1.5 × 10^?5 torr and 2.5 × 10^?5 torr of oxygen agree fairly well with the predictions. Surface self-diffusion measurements at high temperatures may be erroneous if evaporation is not considered, an example for Mo at 2150°K is given.     

Synthesis of 5-aza-analogues of angucyclines: manipulation of the 2-deoxy-C-glycoside subunit

Based on a heterocyclic Diels-Alder strategy, a concise synthesis of 5-aza-analogues of angucyclines bearing a 2-deoxy-C-glycoside subunit is reported. Starting from a common intermediate, a peracetylated D-2-deoxyglucose could be linked to carbons C9 or C10 of the tetracyclic framework. Further manipulations of the sugar residue allowed the installation of bromo and azido substituents at carbon C6′.