Totalsynthese und absolute Konfiguration von natürlichem Multifloramin

The diphenol 1 was resolved into its antipodes and their absolute configuration was established. The levorotatory isomer R-(?)- 1 was oxidized to the dienone R-(?)- 6 , which was rearranged to afford natural (?)-multifloramine (R-(?)- 7 ), thus establishing that the latter has the R-configuration. By the same reaction sequences, the enantiomeric diphenol S-(+)- 1 was transformed to provide (+)-multifloramine (S-(+)- 7 ) of the S-configuration.     

Synthese von natürlichen Haloindolen via Hetero-Cope-Umlagerung von Vinyl-N-phenylhydroxamaten

Synthesis of Natural, Halogenated Indoles via Hetero-Cope Rearrangement of Vinyl N-Phenylhydroxamates An efficient method for the synthesis of natural 4-chloro-6-methoxyindole (the promutagen from fava beans) and of the two 4,6- dibromo- and 3,4,6-tribromoindoles (produced by acorn worms, Enteropneusta) is presented. The key step is a hetero-Cope rearrangement of the intermediate N-phenyl-O-vinylhydroxylamine derivatives.     

Die Strukturdynamik von Pentadienylmetall-Verbindungen mit endständiger Alkyl-Gruppe: zugleich «stereoselektive» und «stereodefensive» Synthese eines natürlichen Riechstoffes

Structural Dynamics of Pentadienyl Metal-Compounds Bearing a Terminal Alkyl Substituent: Both ‘Stereoselective’ and ‘Stereodefensive’ Synthesis of a Natural Perfume . The (2Z, 4E)-, (2E, 4Z)- and (2E, 4E)-isomers of 2,4-decadien-1-ol (5) have been obtained with high and predictable stereochemical homogeneity starting from both (Z)- and (E)-1, 4-decadiene. These hydrocarbons were hydroxylated in a reaction sequence consisting of metallation (by means of s-butyllithium or butyllithium/potassium-t-butoxide, giving rise to organometallic intermediates of specific conformation), dimethoxyborylation and oxidation. The different decadienols as well as (2E, 4Z)-2, 4-undecadien-1-ol were converted into the isovalerates, the ester derived from (2E, 4Z)-2, 4-decadien-1-ol being a natural flavor component.     

Stereoselektive Totalsynthese von natürlichem Phytol und Phytolderivaten und deren Verwendung zur Herstellung von natürlichem Vitamin K1

Steroselective Total Synthesis of Natural Phytol and Derivatives thereof; Use of these Compounds in the Synthesis of Natural Vitamin K₁ The Li₂CuCl₄-catalyzed couplings of the easily accessible bifunctional C₅ allylic acetates (E)- 18a and (E)- 18b with racemic hexahydrofarnesylmagnesium bromide ((3 RS/RS, 7 RS/SR)- 19a ) proceed with high chemo- and stereoselectivity (≥98% (E)-retention) to give the (2E, 7 RS/RS, 11 RS/SR)-phytol derivatives 1a and 1b , respectively, in yields of 72–80% (Scheme 5). The same couplings performed with optically active hexahydrofarnesylmagnesium bromide (3 R, 7 R)- 19a yielded the (E)-phytol derivatives of the natural series (7 R, 11R)- 1a and (7 R, 11 R)- 1b. Acid-catalyzed hydrolysis of(2 E, 7 R, 11 R)- 1b gave natural phytol((2 E, 7 R, 11 R)- 1c ) Friedel-Crafts alkylation of ‘menadiol monobenzoate’ 11b with (2 E, 7 R, 11 R)- 1a or (2 E, 7 R, 11 R)- 1b gave the dihydrovitamine K₁ derivative (2 E/Z, 7′ R, 11′R)- 12b ((E/Z)≈? 9:l). Conversion of configurationally pure (2 E, 7′ R, 11′ R)- 12b (yield 73%; obtained after chromatographic removal of the (Z)-isomer) into natural vitamine K₁ ((2 E,7′ R, 11′ R)- 2 ) was achieved in the usual way by saponification and oxidation with air. Some further investigations of the coupling reactions of bifunctional C₅ allylic synthons with hexahydrofarnesylmagnesium bromide (3 RS/RS, 7 RS/SR)- 19a showed the outcome of these reactions to be critically dependent on the nature of the leaving group, the double-bond geometry and the nature and concentration of the catalyst. Thus, the Li₂CuCl₄-catalyzed couplings of (3 RS/RS,7 RS/SR)- 19a with the allylic halides 29a and 29c as well as with p-toluenesulfonate 29b yielded besides the phytol derivatives 1a and 1b - also the S_N2′-type products 30a and 30b (Scheme 8, Table 2); the same result was found for the coupling with the cis-configurated allylic acetates (Z)- 18a and (Z)- 18b (Table 3). A similar loss of chemo selectivity as well as the loss of stereoselectivity in the coupling reactions of 19 with the bifunctional (E)-olefins of type 18 was observed when the Li₂CuCl₄-catalyst concentration was increased from 0.2 to 25 mol-% or upon substitution of Li₂CuCl₄ by copper (I) chloride or iodide (Table 4).     

Totalsynthese eines Neobetanidin-Derivates und des Neobetenamins

The total synthesis of a neobetanidine derivative ( 3b ) is described. Preliminary experiments led to the synthesis of neobetenamine ( 4 ), which presents the ring system of neobetanidine ( 3 ). A general method for the synthesis of several compounds containing the essential neobetanidine chromophore (a 1, 7-diazaheptamethine system incorporating a pyridine ring) consisted of Vilsmeier-Haack condensations involving the active (enolizable) methyl group of γ-picoline. Neobetenamine ( 4 ) resulted from this reaction with N-formyl-indoline, and also by an amine exchange between indoline and the Vilsmeier-Haack product from γ-picoline and N-methyl-formanilide. The methyl group of γ-picoline-2, 6-dicarboxylic ester 9 , however, was resistant to the Vilsmeier-Haack condensation, but could be activated by introduction of a carboxyl into it: 4-chloropyridine-2, 6-dicarboxylic ester ( 11a ) (from chelidamic ester) was used to alkylate malonic ester. The product ( 12a ) lost only one carboxyl group when saponified. The resulting 2, 6-dicarboxy-pyridine-4-acetic acid ( 13a ) readily underwent a novel decarboxylative condensation with the Meerwein acetal of dimethyl formamide to 4-(2-dimethylamino-vinyl)-2, 6-dimethoxycarbonyl-pyridine ( 14b ), the first synthetic derivative of a neobetalaine. The enamine 14b was subjected to amine exchange reactions with indoline to 2-decarboxy-5, 6-dideoxy-neobetanidine dimethyl ester ( 15 ), and with (S)-cyclodopa ( 16 ) 5, 6-di-O-methyl-neobetanidine trimethyl ester ( 3b ). The latter was identical with the diazomethane transformation product of betanidine ( 1 ), the aglucone of the pigment of the red beet, betanine. A few proton resonance and electron spectral properties, as well as the basicities of several of the synthesized compounds, are tabulated and discussed as far as they express special structural and electronic features of the common 1, 7-diazaheptamethine chromophore.     

Anwendung von ionenaustauschverfahren zur bestimmung von spurenelementen in natürlichen wässern—I: Kobalt

Two methods are described for the determination of cobat lin natural waters. In the first the sample is acidified with HCl, then ascorbic acid and potassium thiocyanate are added, and the solution is run through a column of strongly basic anion-exchanger (Dowex 1-X8). The cobalt thiocyanate complex is retained on the column while other ions are washed through with a mixture of organic solvent and aqueous HCl. The cobalt is then eluted with purely aqueous 6M HCl and determined photometrically with nitroso-R salt. In the second method, (for very dirty samples) the filtered sample is taken through a multi-step evaporation procedure and then added to the column in the mixed solvent. Results are presented for many samples collected in Lower Austria.

Résumé

On décrit deux méthodes pour la détermination du cobalt dans les eaux naturelles. Dans la premiére l'échantillon est acidifié par HCl, puis on ajoute de l'acide ascorbique et du thiocyanate de potassium, et la solution est passée sur une colonne d'échangeur d'anions fortement basique (Dowex 1-X8). Le complexe de thiocyanate de cobalt est retenu sur la colonne tandis que les autres ions sont lavés avec un mélange de solvant organique et de HCl aqueux. Le cobalt est alors élué avec HCl 6M purement aqueux et dosé photométriquement avec le sel nitroso-R. Dans la seconde méthode (pour les échantillons trés sales), l'échantillon filtré est soumis à une technique d'évaporation multistades puis ajouté à la colonne dans le solvant mixte. On présente des résultats pour de nombreux échantillons prélevés en Basse-Autriche.