β‐Sinensal (2,6‐dimethyl‐10‐methylene‐dodeca‐2,6,11‐trienal) was synthesized from the diene‐aldehyde 5. This was converted into the trans‐ and cis‐triene‐aldehydes 16 and 17, which were condensed with the phosphorane 18 to give the corresponding two geometrical isomers (3 and 19) of β‐sinensal.
sun moves around the galactic nucleus in a circular orbit whose radius is approximately 30000 light years, and completes the orbit in 200 million years. The nucleus and disk are surrounded by a n almost spherical halo, which contains the globular star clusters as well as the high velocity stars and subdwarfs. Spectral ClassificationThe spectra of stars are arranged according to two parameters: a) Spectral types (S) 0 €3 A F G K M which constitute a sequence in which the effective temperature decreases from left to right. b) Luminosity classes (LC) I-V which correspond essentially t o a decreasing absolute brightness; I = supergiants; V = main sequence stars. The older Harvard classification was elaborated by Morgan and Keenan t o yield the M K classification generally used today.The relatively few stars which do not fit into the two-parameter scheme are denoted as "peculiar", e.g. the Ap stars with strong magnetic fields. This article describes the first results of investigations directed toward the development of synthetic pathways [9] to compounds with the corrin structure. (11The concept underlying our work is patterned on a type of reaction that seems predestined for the construction of the conjugated unsaturated carbon-nitrogen chain typical of the corrin chromophore, viz. C+C condensation of carbanionoid carbon centers with C = N double bonds of imino ether derivatives [lo] (Scheme 1). The Scheme 1. The reaction principle used for the synthesis of the corrin chromophor.[9] Cf. also R. verification of such a scheme hinges on the availability of the trialkyloxonium salts discovered by Meerwein et al.[l 11 as reagents that allow a reliable conversion of amide or lactam groups into the corresponding imino ether derivatives.the development of a synthetic route to the corrin type of structure was inspired by the substitution pattern present in natural corrin complexes; moreover, it circumvents dangers of isomerization and dehydrogenation COOCH, The synthetic route is illustrated by the formulae of the bicyclic intermediates ( 2 ) and (3) ; their combination in the sense shown is intended to yield a derivative of that might well lie along the path to the unsubstituted corrin. Scheme 2 shows a synthesis of the left-hand structure (2). The monocyclic tetraester (4), readily prepared by Diels-Alder addition of tetramethyl ethylenetetracarboxylate onto isoprene, is smoothly converted into the aliphatic tetraester ( 5 ) by a novel reductive ring-cleavage with sodium in liquid ammonia. The position and configuration of the double bond in ( 5 ) is unambiguously defined by the method of formation.[I 21 With the exception of the sodium salt (1 71, all the compounds shown in Schemes 2-4 gave correct elementary analyses. The data denote the following: mwL: maxima in the ultraviolet spectrum in ethanol; log E values in brackets. cm-1: characteristic bands in the infrared spectrum in CHCI,. ppm: selected signals referred to ( 3The crystalline diamide (6) is the starting material for a sequence of operations leading to steros...
A m Beispiel der Synthese des Nickel(II)-Komplexes des (&)-I .8.8.13.13-Pentamethyltrans-corrins wird ein synthetischer Zugang zurn Verbindungstyp der Corrine aufgezeigt. Durch die mehrfache Verwendung des Triathyloxonium-tetrafluorborats bietet die Arbeit eine Illustration der praparativen Bedeutung der von H . Meerwein und Mitarbeitern entdeckten Trialkyloxoniumsalze. Als Corrin ( I ) [3] bezeichnet man das hypothetischeGrundsystem des porphyrinoiden Ligandgerustes, welches in Form eines Cobaltkomplexes den besonderen Strukturtypus des Vitamins BIZ [4] verkorpert. Unsere Kenntnisse von der Konstitution dieses Systems stammen aus einer vor rund einem Jahrzehnt von D. Crowfoot-Hndgkin und Mitarbeitern in Oxford durchgefuhrten, nunmehr klassischen Serie rontgenographischer Strukturanalysen [5]. Die damals der organischen Na-[ I ] Gestorben am 12. Dezember 1963. 121 Rontgenanalytische Abteilung des Organisch-Chemischen Laboratoriums, ETH, Zurich. [3] Um die trans-Verknupfung der Ringe A und D, wie sie in den Vitamin-B12-Verbindungen vorliegt, zum Ausdruck zu bringen, verwenden wir hier fur das System (Z) die Bezeichnung ,,trans-Corrin". Bei allen Verbindungen mit chiraler Struktur handelt es sich in dieser Arbeit um die racemischen Formen. [4] R.
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