03 Fakultät Chemie
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Item Open Access Darstellung von Didehydropyridinen aus (Trimethylsilyl)pyridinen(1991) Effenberger, Franz; Daub, WolfgangHalogen-substituted (trimethylsilyl)pyridines 2, 3, 5 - 7 and trifluoromethylsulfonyloxy-substituted (trimethylsilyl)pyridines 9b, 11b are obtained from 2- and 3-halopyridines 1, 4 or hydroxypyridines 8, 10, and 12. Reactions of the 3- and 2-(trimethylsilyl)pyridines 2,9b and 11b with bases in the presence of furans 15 give only protodesilylation or hydrolysis products but no indication is found for the formation of a 2,3-didehydropyridine. 3-Bromo-4-(trimethylsilyl)pyridine (5a) reacts with KOCMe3 in the presence of furan (15a) to give a mixture of products from which the isoquinoline derivative 20 and the tert-butoxypyridines 23, 24 are formed by addition to 3,4-didehydropyridine. Under comparable conditions far higher yields of 3,4-didehydropyridines are obtained by treatment of the 3-halo-2,4-bis(trimethylsilyl)pyridines 7 with strong bases.Item Open Access Enantioselektive Veresterung racemischer Cyanhydrine und enantioselektive Hydrolyse oder Umesterung racemischer Cyanhydrinester mittels Lipasen (Enzym-katalysierte Reaktionen ; 7)(1991) Effenberger, Franz; Gutterer, Beate; Ziegler, Thomas; Eckhardt, Elisabeth; Aichholz, ReinerIn der vorliegenden Arbeit berichten wir zusammenfassend über die enantioselektive Hydrolyse oder enantioselektive Umesterung racemischer Cyanhydrinester und über die enantioselektive Veresterung racemischer Cyanhydrine mittels Lipasen.Item Open Access Properties of amphiphilic terminally substituted conjugated nonaene- and 2-docosylnonaene carboxylic acids in monolayers at the air-water interface(1991) Effenberger, Franz; Meller, Paul; Ringsdorf, Helmut; Schlosser, HubertIn the present communication, we report thesynthesis of conjugated nonaene- and 2-docosylnonaene carboxylic acids with different terminal substituents. These substituents have been chosen so that their spectroscopic properties differ from those of the polyene chain; they also have specific electron donor, electron acceptor or redox properties to allow for specific and selective excitation (energy intake). Because of the amphiphilic character of these compounds, pressure-area isotherms were determined in monolayers at the air-water interface.Item Open Access Darstellung und stereoselektive Reaktionen von (R)-α-Sulfonyloxynitrilen(1991) Effenberger, Franz; Stelzer, UweHier berichten wir über eine wichtige Erweiterung des Synthesepotentials optisch aktiver Cyanhydrine durch Uberfiührung der Hydroxygruppe in eine gute Austrittsgruppe. Besonderes Interesse kommt dabei den Reaktionen der Cyanhydrinderivate zu, bei denen der Stickstoff der Cyangruppe im Molekül erhalten bleibt, da Verbindungen dieses Typs nicht direkt iüber α-Amino- oder α-Hydroxycarbonsäuren zugänglich sind.Item Open Access Darstellung von (R)-2-(Sulfonyloxy)nitrilen und ihre Reaktionen mit Acetaten : Konfigurationsumkehr optisch aktiver Cyanhydrine (Enzym-katalysierte Reaktionen ; 15)(1993) Effenberger, Franz; Stelzer, Uwe2-(Sulfonyloxy)nitriles (R)-6, 7, 8 are obtained in high optical purity from the respective cyanohydrins (R)-2 by sulfonylation with methanesulfonyl chloride (3), toluenesulfonyl chloride (4), and trifluoromethanesulfonic anhydride (5), respectively. In contrast to the aliphatic (sulfonyloxy)nitriles (R)-6, 7, 8a - e, the benzylic-type mandelic acid derivatives (R)-7,8í are unstable at higher temperature. The 2-(sulfonyloxy)nitriles (R)1- 6, 7, 8a - e react at room temperature with alkali acetates in a typical SN2 manner to give the cyanohydrin acetates (S)-9 in high optical purity. Under these reaction conditions, however, the mandelic-type compounds (R)-7, 8í partly racemize and decompose. By hydrolysis of the acetates (S)-9, (S)1-cyanohydrins (S)-2 of aliphatic aldehydes are easily available.Item Open Access Nucleophile Substitution von Nitrit in Nitrobenzolen, Nitrobiphenylen und Nitronaphthalinen(1991) Effenberger, Franz; Koch, Markus; Streicher, WilliAromatic compounds, accessible only by multistep procedures, can be synthesized easily by nucleophilic substitution of nitrite in nitrobenzenes, nitrobiphenyls, and nitronaphthalenes. Thus, meta-substituted phenols 3, 4, and 7 are obtained from 1,3-dinitrobenzene (1) and meta-substituted nitrobenzenes 6, as well as 3,5-disubstituted phenols 10 and 5-substituted resorcinol derivatives 11 from 3,5-disubstituted nitrobenzenes 9. The unsymmetrically substituted nitrobiphenyls 13, 15, 17, 19, 21, 23, 24, and 26 are also available by nitrite exchange from the corresponding easily accessible dinitrobiphenyls 16, 18, 20, 22, and 25. A nitrite exchange with nucleophiles is easily possible in the 1,5-disubstituted naphthalenes 29, 34, while in the case of the 1,8-disubstituted naphthalenes 31, 36 only the chloro derivative 36 undergoes this exchange under much stronger conditions in low yield.Item Open Access Stereoselektive Darstellung von 2-Aminoalkoholen aus (R)- und (S)-Cyanhydrinen (Enzym-katalysierte Reaktionen ; 8)(1991) Effenberger, Franz; Gutterer, Beate; Ziegler, ThomasIn der vorliegenden Arbeit berichten wir über die strukturellen Einflüsse auf die Diastereomerenbildung bei der Hydrierung mittels NaBH4 der aus O-Trimethylsilyl-geschützten (R)-Cyanhydrinen mit Grignard-Verbindungen in situ erhaltenen Imino-Verbindungen A zu (1R,2S)-2-Aminoalkoholen. In den zitierten Publikationen werden lediglich Beispiele für (R)-Arylcyanhydrine beschrieben, wobei in der Regel keine optisch reinen (R)-Cyanhydrine eingesetzt wurden und darüber hinaus die erhaltenen Rohprodukte erst durch Umkristallisation gereinigt wurden, so daß korrekte Aussagen über die Diastereoselektivitat der Hydrierung der Imino-Verbindungen A nicht möglich sind.Item Open Access 5-Dimethylamino-5'-nitro-2,2'-bithiophene : a new dye with pronounced positive solvatochromism(1993) Effenberger, Franz; Würthner, Frank-Item Open Access Experimental and theoretical aspects of the formation of radical cations from tripyrrolidinobenzenes and their follow-up reactions(1990) Effenberger, Franz; Stohrer, Wolf-Dieter; Mack, Karl Ernst; Reisinger, Friedrich; Seufert, Walter; Kramer, Horst E.A.; Föll, Rudolf; Vogelmann, EkehardtTripyrrolidinobenzene radical cations(1*+), obtained from the corresponding arenes by oxidation with silver nitrate, are specially stabilized and thus allow specific reaction pathways of arene radical cations to be investigated separately and individually. Radical cations 1*+ ,for instance, generated under exclusion of oxygen, undergo dimerization to 2, or they abstract hydrogen from the solvent to form 3. In a pure oxygen atmosphere, the O2 reaction products 6 and 7 are formed, respectively, either exclusively or together with 2 and 3. Kinetic measurements give the following order of reactivity for these individual processes: reaction with O2 > dimerization. > H-abstraction from solvent. The changes in the product spectrum upon modification of the reaction conditions are in accord with the kinetic results. The dimeric u complexes 2 show surprisingly facile dissociation into two radical cations, two (1*+)with a much higher dissociation rate for the alkyl derivatives 2b-d than for 2a. Dissociation is enhanced substantially by light or in the presence of π donors. Individual product formation, rate of reactions of the radical cations 1*+, and photochemical cleavage of the dimeric σ complexes 2 can be rationalized, by qualitative and quantitative MO considerations, in terms of their relative frontier orbital energies.Item Open Access Kinetic analysis and simulation studies for lipase-catalysed resolution of racemic 2-methyl-1-pentanol(1993) Indlekofer, Michael; Reuss, Michael; Barth, Stefan; Effenberger, FranzThe lipase-catalysed optical resolution of a racemic mixture of 2-methyl-1-pentanol by transesterification using vinyl acetate as acyl donor has been studied experimentally. A mechanistic model has been developed for the double-substrate reaction sequence treating both enantiomers as competing substrates. The model is based upon a ping-pong mechanism with alternative substrates involving an acyl-enzyme intermediate. The kinetic constants of the model have been evaluated using initial rate experiments and nonlinear regression analysis. The model successfully predicts the evolution of the enantiomeric excess of substrate (eeR) and the degree of conversion with time for batch experiments with various initial concentrations of vinyl acetate and (R,S)-2-methyl-1-pentanol. Furthermore, the rate equations have been used to theoretically study the dynamic progression of a continuous enzyme-catalysed resolution process. The enantiomeric excess as a function of conversion for different process configurations is discussed. It is found, that the maximum attainable eeR is strongly dependent on the residence time distribution of the continuous reactor and is rather low for a continuous stirred tank reactor (CSTR) due to competitive inhibition effects.