Beiträge zur Chemie der Pyrrolpigmente, 38. Mitt.: Zur Assoziation von Gallenpigmenten

The long standing problem of solvent dependent absorption spectra of certain bile pigments such as bilirubindimethylester has been solved by measurement of molecular masses by means of vapour pressure osmometry. Using this method and the investigation of the concentration and temperature dependence of the absorption spectra on several model compounds an association equilibrium for pigments of the rubinoid structural type could be confirmed. Moreover the optical properties of the coexisting species and the corresponding equilibrium constants could be deduced by spectroscopic techniques. Verdinoid pigments lacking free carboxylic functions on the other hand tend to be monomeric in solution. A heteroassociated species involving equimolar amounts of a verdinoid and a rubinoid pigment could be verified existing on adsorbents like silicagel.

37. Mitt.:Falk, H., Thirring, K., Tetrahedron, im Druck.     

Intramolecular Diels-Alder reactions: Construction of aza- and diaza-steroid type skeletons

The preparation of 2-(4-phenyl)butadienyl-piperidine 5 is described. An intramolecular Diels-Alder reaction of the intermediately formed fumaramide thereof produces stereoselectively the tricyclic lactam 6 . Its structure, as well as the configurational relationship of its 5 asymmetric centers, is corroborated on the basis of the NMR.-data. Cycloacylation of the thermodynamically stable precursors 13 and 20 leads to pentacyclic aza- or diaza-steroid type skeletons. Their structures ( 14, 16 , and 21 ) and in particular their relative configurations are elaborated. A few qualitative kinetic aspects of this intramolecular (4+2)-cycloaddition are presented.     

Photochemisches Verhalten von 1- und 2-alkylierten 1, 2-Dihydronaphthalinen bei tiefen Temperaturen

The irradiations of 1, 1-dimethyl- (8), 1, 1-di-(tri-deuteriomethyl)- (d₆– 8 ), 1, 1, 2, 2-tetramethyl- ( 9 ) and cis- and trans-1, 2-dimethyl-1, 2-dihydronaphthalenes (cis- and trans- 10 ) were investigated in 2, 2-dimethylbutane/pentane at ?100° using a mercury high-pressure lamp, and with mercury high- and low-pressure lamps at room temperature. The results were compared with one another, and those of the individual compounds are collected in schemes 2 and 4–7. The most important results are the following: 1. The 1, 2-dihydronaphthalenes undergo a conrotatory ring opening to the o-quinodimethanes on irradiation with high- or low-pressure lamps at room temperature or at ?100°. Thermal reactions ([1, 7a]H-shifts, electrocyclisations) are suppressed at ?100°. The o-quinodimethanes formed from 8 (scheme 2), 9 (scheme 5) or cis- 10 (scheme 6) undergo on irradiation with the high-pressure lamp, [1, 5]H-shifts or photochemical Diels-Alder reactions after renewed photochemical excitation, to yield the benzobicyclo[3.1.0]hex-2-ene derivatives. These Diels-Alder reactions do not proceed stereospecifically, and therefore are not orbital symmetry controlled reactions. 2. If the 1, 2-dihydronaphthalenes are irradiated at room temperature with either a high- or a low-pressure lamp, then the initially formed o-quinodimethanes undergo thermal [1, 7a]H-shifts, in preference to all other reactions, as long as this is sterically possible; the resulting products can undergo secondary photochemical transformations. Such o-quinodimethanes are formed on irradiation of 8, 9 and cis- 10 . From trans- 10 , an o-quinodimethane mixture is formed, of which one component (cis, cis- 22 ) undergoes thermal [1, 7a] H-shifts, while the other (trans, trans- 22 ) suffers a thermal disrotatory electrocyclisation to give cis- 10 . If a high-pressure lamp is used in the last experiment, then the competing photochemical Diels-Alder cyclisation to bicyclic compounds of the type 23 (scheme 7) can result in the trans, trans- 22 . As was shown by Salisbury [3], and confirmed by ourselves in other cases [2], photochemical Diels-Alder reactions or [1, 5]H-shifts in the o-quinodimethanes require light of wavelength ? 400 nm (high-pressure lamp). The present photochemical investigations amplify and confirm our earlier conclusions concerning the photochemistry of the 1, 2-dihydronaphthalenes [2].     

Beiträge zur Chemie der Pyrrolpigmente, 70. Mitt.: Zum aktiven Transport mit tripyrrinoiden Liganden

The tripyrrin carboxylic acid6 exhibits a pronounced efficiency for carrier mediated proton driven secondary active transport (counter transport) for a series of toxic or valuable cations in a bulk chloroform membrane. In case of Zn⁺⁺ ions the mechanism including complete concentration profiles forNerst diffusion layers and bulk phase have been established. This compound might be used for detoxification or enrichment of precious metals using membrane separation systems.

Herrn Prof. Dr.A. Neckel mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Das Verhalten der WÄrmeleitfÄhigkeit von Kautschuk bei der Dehnung

Zusammenfassung Mit einer Me\apparatur, die nach einer Relativmethode die W?rmeleitung in fadenf?rmigen Kautschukvulkanisaten zu messen gestattet, wird der Einflu\ der Dehnung auf die W?rmeleitf?higkeit untersucht. Es ergibt sich ein wesentlicher Anstieg der W?rmeleitung mit der Dehnung bei allen untersuchten Materialien. Bei stark vulkanisiertem Kautschuk ist dieser Anstieg am geringsten, bei Polybutadienen ist er h?her als bei Naturkautschuk. Auf Grund von bekannten Vorstellungen über die Kinetik der hochpolymeren Moleküle bei Dehnung und über die Ausbreitung von W?rmewellen in Festk?rpern werden die Beobachtungsergebnisse gedeutet. Dabei wird festgestellt, da\ der Anstieg der W?rmeleitf?higkeit auf eine zunehmende Ausrichtung von Molekülkettenabschnitten in Dehnungsrichtung — die zugleich Richtung des W?rmestromes ist- und auf eine Abnahme der Zahl der Streuzentren für die W?rmewellen zurückzuführen ist. Auch Unterschiede bezüglich des Betrages des Anstiegs, den die einzelnen Materialien zeigen, k?nnen z. T. auf Grund dieser Vorstellungen erkl?rt werden.