Synthesen von Moniliformin,einem Mycotoxin mit Cyclobutendion-Struktur

Syntheses of Moniliformin, a Mycotoxine with a Cyclobutenedione Structure Six different routes to 3-hydroxy-3-cyclobutene-1, 2-dione ( 4 ), the free acid of the mycotoxine Moniliformin (=alkali salt of 4 ) are described. A common feature of all pathways is the synthesis of cyclobutanes having the oxidation level 6. Moniliformin precursors which are easily transformed to 4 by acid catalysed hydrolysis include [2+2]-cycloadducts of ketene with tetraalkoxy-olefins, 3,4,4-trialkoxycyclobutenes, derivatives of polyfluorinated cyclobutenes, the brominated [2+2]-cycloadduct of ethyl vinyl ether and dichloroketene, tetrabromocyclobutanone, [2+2]-photocycloadducts of dichlorovinylenecarbonate with dichloroethylenes, and the dimer of chloroketene. The most convenient synthesis via the [2+2]-cycloadduct of tetraethoxyethylene and ketene ( 14b ) is reported in detail and produces 4 in four simple steps in 57% overall yield. In addition, two new syntheses of squaric acid ( 56 ) are described.     

Über die Reaktion einiger 2H-Pyran-2-on-Derivate mit primären Aminen

On the Reaction of Some 2H-Pyran-2-one Derivatives with Primary Amines The versatile reactivity of 6-unsubstituted 2H-pyran-2-ones towards aliphatic and aromatic amines has been studied. It was found that the result of the reaction depends not only on the substitution of 2H-pyran-2-ones and on the structure of amines, but also on the stoichiometric ratio of reacting compounds.     

Neue Derivate der 2-Phenyl-benzo[b]thiophen-3-carbonsäure

Zusammenfassung 2-Phenyl-5-methoxy-benzo[b]thiophen-3-carbonsäure und 2-Phenyl-5,6-dimethoxy-benzo[b]thiophen-3-carbonsäure wurden durch Ringschlußreaktionen hergestellt und in eine Reihe von Säureamiden und basisch substituierten Estern übergeführt.

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New derivatives of 2-Phenyl-benzo[b]thiophene-3-carboxylic acid

2-Phenyl-5-methoxy-benzo[b]thiophene-3-carboxylic acid and 2-phenyl-5,6-dimethoxy-benzo[b]thiophene-3-carboxylic acid, prepared by ring closure reactions, were used for the synthesis of amides and of basically substituted esters.

     

Recent results from the TCV tokamak

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0B _tor1.46T,I _p800kA,k2.05, –0.71. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s^–1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors ( _tor aB/I _p) up to two and densities up to 2.25×10²⁰m^–3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×10²⁰m^–3 have been obtained in elongated D-shaped plasmas with 360 kAI _P600 kA.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was partly supported by the Fonds National Suisse de la Recherche Scientifique.     

Reagents for new heteroannelation reactions III. 2-(Methylthio)-2-thiazoline

Summary A variety of partly novel tri- and tetracyclic hetero systems were obtained by reaction of heteroaromatic 2-aminoesters with 2-(methylthio)-2-thiazoline, yielding double-annelation of a thiazolo[2,3-b]pyrimido moiety in a one-pot process.On leave from University of Chittagong, Bangladesh     

Proton and lithium cation affinities calculated with floating orbital geometry optimization (FOGO)

The FOGO method is used to calculate proton affinities and lithium cation affinities. The molecules of primary interest in this study are the methyl-substituted amines. In addition, the lithium cation affinity of HF, H₂O, CH₃OH, H₂CO, and HCN are calculated for comparison. Geometries of all species are fully optimized with a double-zeta (DZ) basis set, including polarization on hydrogen and the first-row elements by floating orbitals. Comparison with experimental values demonstrates that structural data and proton affinities resulting from this type of ab initio calculation are of chemical accuracy. The lithium cation affinities are also reasonably well reproduced, but the small experimental differences are not within the accuracy, which can be expected from this type of calculation.     

Geometry optimization in ab initio SCF calculations: Part IV. Energy barriers and dipole moments obtained with floating orbital geometry optimization (FOGO)

The floating orbital geometry optimization (FOGO) described previously is applied to H₂O₂, NH₃, HNC, HNO, HNCO, and CH₃OH. In the FOGO method we apply two analytically calculated energy gradients in a variable metric method. Some orbitals are no longer fixed on the corresponding nuclei, but their position is optimized simultaneously with the nuclear coordinates. It is shown that relative energies (e.g. rotational barriers) are obtained with similar accuracy to basis sets including polarization functions. Further, it is confirmed that FOGO yields excellent dipole moments. The FOGO method involves a considerable time saving compared to conventional calculations with DZ + P basis sets.     

Untersuchungen über Phenthiazinderivate. 10. Mitteilung

Zusammenfassung Es wurde ein allgemein anwendbarer Weg zur Herstellung von in -Stellung basisch substituierten 4,10-Trimethylenphenthiazinen durch Umsetzung der aus den -Hydroxyverbindungen erhaltenen -Bromverbindungen mit sekundären Aminen angegeben. Für das in der Literatur bekannte -Amino-4,10-Trimethylen-phenthiazin wurden neue Darstellungen beschrieben.     

Untersuchungen über Phenthiazinderivate, 17. Mitt.: Über Strukturfragen bei der LiAlH4-Reduktion des 4, 10-(α-Hydroximino-trimethylen)-phenthiazins

Zusammenfassung Je nach den Reaktionsbedingungen entstehen verschiedene Produkte bei der Reduktion des 4,10-(-Hydroximino-trimethylen)-phenthiazins. Durch Vergleich mit Verbindungen bekannter Struktur wurde der Beweis erbracht, daß die von uns schon früher für das Produkt der Natriumamalgamreduktion angenommene Struktur richtig ist.Mit 2 Abbildungen     

Partial Synthesis and Characterization of the Mono-and Diepoxides of β-Cryptoxanthin

β-Cryptoxanthin ( 1 ) was acetylated and then epoxidized with monoperoxyphthalic acid. After hydrolysis, repeated chromatography, and crystallization, (3S,5R,6S)-5,6-epoxy-β-cryptoxanthin ( 3 ), (3S,5S,6R)-5,6-epoxy-β-cryptoxanthin ( 4 ), (3R,5′R,6′R)-5′,6′-epoxy-β-cryptoxanthin ( 5 ), (3S,5R,6S,5′R,6′S)-5,6:5′,6′-diepoxy-β-cryp-toxanthin ( 6 ), and (3S,5S,6R,5′S,6′R)-5,6:5′,6′-diepoxy-β-cryptoxanthin ( 7 ) were isolated as main products and characterized by their UV/VIS, CD, ¹H- and ¹³C-NMR, and mass spectra. The comparison of the carotenoid isolated from yellow, tomato-shaped paprika (Capsicum annuum var. lycopersiciforme flavum) with 3–5 strongly supports the structure of 3 for the natural product.