Ein neuer synthetischer Zugang zu Ubichinonen

A New Synthetic Route to Ubiquinones Ubiquinones 11 have been prepared employing a new strategy: as key step, the Diels-Alder reaction of 1,1,2-trichloroethene 3 with 2,5-bis[(trimethylsilyl)oxy]-3-methylfuran ( 2 ) has been used for the construction of the quinone part. After methanolysis of the [4 + 2] adducts 4a/4b , further reaction with cyclopentadiene and substitution of the Cl-atoms by MeO groups, the intermediate 7 is obtained. Diketone 7 can easily be alkylated with the desired polyprenyl side chain 9 (X = Br) using a strong base to yield, after a retro-Diels-Alder reaction, the corresponding ubiquinones 11 in high yields.     

Neue Wege zu Pentalen-Vorstufen

New Pathways to Precursors of Pentalene Pentalene dimers 2 and 3 are easily available in moderate yields by CuCl₂-induced oxidative coupling of dilithium-pentalenediide ( 5 ) (Scheme 1). On the other hand, NBS bromination of 1,5-dihydropentalene ( 4 ) or of 1,2-dihydropentalene ( 8 ) gives unstable 1-bromo-1,2-dihydropentalene ( 9 ), while subsequent in-situ elimination with Et₃N exclusively gives syn-cis-pentalene dimer 2 in moderate yields (Scheme 3). NMR-Spectroscopic evidence for compounds 2 , 3 , and 9 is presented, and mechanistic alternatives for the formation of pentalene dimers 2 and 3 are discussed.     

Abbau von Siliciumtetrafluorid-Amin-Addukten zu Fluorsilylaminen

Zusammenfassung Die Spaltung von Disilazanen und Cyclosilazanen bei 120° durch die Amin-Addukte des Siliciumtetrafluorids F₄Si(LH)₂ (mitLH=NH₃,meNH₂ ⁶, N₂H₄, NC₅H₅) führt nach den SchemataA, B oderC (Seite 1190) zu den Fluorsilylaminen Fme ₂Si(NHSime ₂) _n F (mitn=1 und 2) sowie (me ₃SiNH) _n SiF_4–n (mitn=1, 2 und 3). Ihre chemischen, physikalischen und spektroskopischen Eigenschaften werden mitgeteilt.

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Cleavage of disilazanes and cyclosilazanes at 120°C by F₄Si(LH)₂ addition compounds (LH=NH₃,meNH₂ ⁶, N₂H₄, NC₅H₅) yields, following the schemesA, B orC (page 1190), the fluorosilylamines Fme ₂Si(NHSime ₂) _n F (n=1 and 2) and (me ₃SiNH) _n SiF_4–n (n=1, 2 and 3). Their chemical, physical and spectroscopic properties are described.

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Mit 1 Abbildung

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68. Mitt.:U. Wannagat, K. Hensen, P. Petesch, F. Vielberg undH. Voß, Mh. Chem.99, 438 (1968).

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Zugleich 9. Mitt. über Verbindungen von Nichtmetallhalogeniden mit Pyridin und seinen Homologen; 8. Mitt.: siehe¹.

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Vorläufige Mitt.:U. Wannagat undH. Bürger, Angew. Chem.76, 497 (1964).

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Sonderdrucke überU. W., D-33 Braunschweig, Pockelsstr. 4; Institut für Anorg. Chem. der Techn. Universität.

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Mit Auszügen aus der DissertationF. Höfler, Techn. Hochschule Graz 1967.     

Kobalt-katalysiert Cycloadditionen von Alkinen und Nitrilen zu Pyridinen: Ein neuer Zugang zu Pyridoxin (Vitamin B6)

Cobalt-Catalyzed Cycloaddition of Alkynes and Nitriles to Pyridines: A New Route to Pyridoxine (Vitamin B₆) A new synthesis of pyridoxine hydrochloride ( 1 ) based on a Co-catalyzed cycloaddition of MeCN with substituted di(2-propynyl) ethers ( 3 and 16 ) is described. The reaction sequences following cycloaddition and leading to 1 involve as key steps the rearrangement f the pyridine-N-oxide 6 to the 3-hydroxypyridine 7 with Ac₂O and a modified Curtius rearrangement of the acid 19 and subsequent diazotation and hydrolysis to the same pyridoxine precursor 7, respectively. The intermediate 7 is transformed to 1 by well-known procedures.     

Neue Wege zu Polysilanen

Summary Disilane derivatives undergo disproportionation reactions to polysilanes. Investigated were 1,2-dimethyldisilane and 1,2-dimethyltetrachlorodisilane with catalysts like NH₄Cl, AgCN, and Nacyanamide. In case of 1,2-dimethyldisilane, with more than catalytic amounts of NH₄Cl, a nitrogen containing polysilane is formed. Two new compoundsMeSiH(NCO)₂ andMe ₂Si₂(NCO)₄ were synthesized and characterized. The last one leads to a polymer at heating. Additionally an electrochemical formation of polydimethylsilane is described.

     

Wege zu Si-funktionalisierten Organostannylsilanen

Summary Silicon substituted organostannyl silanes are formed by the reaction of stannylallyl silanes with triflic acid and from stannyl-hydrogen silanes and CHBr₃. The structures have been proved by NMR-investigations.

Herrn Prof. Dr.E. Hengge zum 65. Geburtstag gewidmet     

Ein neuer Weg zu Cyclopentasilanderivaten

Summary By means of the new possibility to split a trimethylsilyl group from the methylated cyclopentasilane by action ofEtONa, a new, simple, and effective pathway to valuable molecules for other syntheses was found.

Herrn Univ.-Prof. Dr. Edgar Nachbaur zum 60. Geburtstag gewidmet     

Neue Wege zu 1H- und 2H-Pyrrolen

New Routes to 1H- and 2H-Pyrroles A synthesis of 1H-pyrroles is described starting with pyridine analogues of chalcones and involving the reaction of acetic anhydride with 1-pyrroline-1-oxides. Another route leads from 1-pyrrolines to 2 H-pyrroles via bromination with N-bromosuccinimide and subsequent dehydrobromination in dimethylformamide.     

Ringöffnung von Verdazylen zu N-Formyl-formazanen

Zusammenfassung Verdazyle mit einer Methylenbrücke in 6-Stellung werden in Gegenwart von Carboraffin durch Luftsauerstoff unter Ringöffnung zu N-Formyl-formazanen oxydiert. Mit Acetanhydrid/BF₃-Ätherat ergeben C-Aryl-formazane C-Aryl-N-Acetyl-formazane.

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In the presence of carboraffin verdazyls with a methylene bridge in position 6 are oxidized with atmospheric oxygen under ring opening to N-formyl-formazans. C-Aryl-formazans yield C-aryl-N-formyl-formazans with aceticanhydride/BF₃ etherate.

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Herrn Prof. Dr.F. Wessely zur Vollendung seines 70. Lebensjahres in alter Verbundenheit gewidmet.

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15. Mitt.:F. A. Neugebauer, H. Trischmann undM. Jenne, Angew. Chem.79 (1967), im Druck; 14. Mitt.:F. A. Neugebauer, H. Trischmann undG. Taigel, Mh. Chem.98, 713 (1967).     

Aminierende reduktive Kupplung aromatischer Aldehyde mit niervalenten Titan-Reagenzien zu 1,2-Diarylethylendiaminen

Preparation of 1,2-Diarylethylenediamines by Aminative Reductive Coupling of Aromatic Aldehydes with Low-Valent Titanium Reagents In a novel McMurry- Type one-pot reaction, aromatic aldehydes and secondary amines are poupled of give the N, N, N′, N′-tetraalkyl-1,2-diarylethylendiamines 1–22 (Table 3). To this end, a lithium dialkylamide is added to an aromatic aldehyde to give the adduct B which is then treated with 1 equiv. of TiC1₄ to yield a coloured suspension of a reagent synthetically equivalent to a iminium salt ( C/D in Scheme 4). After treatment with a low-valent Ti reagent which is prepared by reduction of TiC1₄ with either K or, preferably, Mg, the coupling products are isolated in 23 to 81% yield as a 1:1 mixture of the diastereoisomers (meso- and rac-form). These are separated either by chromatography or by crystallization and characterized.     

Anwendungsbreite der reduktiven Kupplung aromatischer Aldimin-Derivate mit niedervalenten Titan-Reagenzien zu 1,2-Diarylethylendiaminen

Scope and Limitations of the Reductive Coupling of Aromatic Aldimine Derivatives with Formation of 1,2-Diarylethylenediamine Units, Using Low-Valent Titanium Reagents Besides the adducts from lithium amides to aromatic aldehydes, iminium salts, animals, and N-silylimines of aromatic aldehydes are coupled by the black suspension obtained from TiCL₄ and Mg turnings in tetrahydrofuran (THF). The 1,2-diarylethylenediamines with tertiary and primary amino groups thus obtained are formed with no or only moderate diastereoselectivity (products 4a–d (Scheme 2) and 5–e (Scheme 3), respectively); the amine component may contain a strained ring or additional heteroatoms as in azetidin, bis(2-methoxyethyl)amine, piperazine, morpholine, and thiomorpholine (products 6a–e ; Table 1). By an in-situ procedure, ethylenediamines exclusively trans-diaryl-substituted piperazine and perhydro-1,4-diazepine derivatives (products 7a–f ; Table 2). Enantiomerically pure monocyclic trans,cis-5-alkyl-2,-3-diaryl-piperazines and diazabicyclo[4.3.0]nonanes and -[4.4.0]decanes are obtained by employing suitable diamines prepared from the amino acids (S)-alanine, (S)-phenylalanine, (S)-proline and from (S,S)- or (R,R)-cyclohexane-1,2-diamine, respectively (products 11a–i , 7e ; Table 4). The configuration of all products are derived from the high-field NMR spectra, some of which are discussed in detail (Figs. 1 and 2, Tables 3 and 5); all new compounds are fully characterized by their physical data. Depending upon the structure of the components employed, the yields of purified products range from as low as 7% to essentially quantitative.     

Gef?rbter Niederschlag zu colorimetrischen Bestimmungen

Zusammenfassung Die Färbung des weißen ZnHg(SCN)₄-Niederschlags zu einem lilapurpurnen Niederschlag durch Spuren Cu und zu einem blauen Niederschlag durch Spuren Co kann colorimetrisch angewendet werden unter Erzielung derselben Genauigkeit wie bei gewöhnlichen colorimetrischen Bestimmungen. Die Empfindlichkeit in beiden Fällen ist ungefähr 10mal größer als die Colorimetrie mit Hilfe von NH₄OH.Die deutlich wahrnehmbaren Grenzkonzentrationen; bei denen noch Färbung mit bloßem Auge sichtbar ist, sind:0,0001% Cu oder Co in Gegenwart von 1% Zn bei völligem Niederschlag.0,00005–0,00001% Cu in Gegenwart von 1% Zn bei unvollkommener Fällung.0,00001% Cu in Gegenwart von 0,01% Zn bei vollständiger Ausfällung. Für qualitative Untersuchungen muß man zur Erzielung der größtmöglichen Empfindlichkeit das Kupfer oder das Kobalt in Gegenwart von ±0,01% Zn mit (NH₄)₂Hg(SCN)₄-Reagens vollständig ausfällen. In Reagensgläsern kann man auf diese Weise leicht 1g Cu in 10ccm und 0,1g Cu in 1ccm erkennen. Auf der Tüpfelplatte nimmt man lieber die Zinkkonzentration etwas größer, um einen deutlichen Niederschlag zu bekommen. Mit einem Volumen von 0,1ccm kommt man zu derselben Grenze von 0,1g Cu oder Co. Mikrochemisch liegt die Grenzkonzentration höher, das zu gebrauchende Volumen ist jedoch kleiner, wodurch die Grenze in 0,01ccm wieder auf 0,1g Cu oder Co steigt.     

Homoleptische Zinkamide: Der Übergang zu monomeren Molekülen

Homoleptic Zinc Amides: Transition to Monomeric Molecules Zinc chloride reacts with the lithium salts of the bulky secondary amines HN(i-Bu)₂ and HN(t-Bu)₂ to form the corresponding homoleptic zinc compounds {Zn[N(i-Bu)₂]₂}₂ ( 1 ) and Zn[N(t-Bu)₂]₂ ( 2 ). The NMR spectroscopic and mass spectrometric results as well as the molecular weight determinations and X-ray diffraction data are consistent with a dimeric structure of 1 and a monomeric structure of 2 in the gas phase, in solution and in the solid state.     

Neue Zugänge zu einigen aromatischen Retinoiden

New Approaches to Some Aromatic Retinoids Starting from 2,3,5-trimethylphenol ( 2 ), two pathways to ethyl (all-E)-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethylnona-2,4,6,8-tetraenoate ( 1 ) and to some of its (Z)-isomers have been developed. The first one is based on a Pd(O)-catalyzed arylation of (Z)-3-methylpent-2-en-4-yn-l-ol ( 6 ) with 4-bromo-2,3,5-trimethylanisol ( 5 ). The acetylenic C₁₅?alcohol 9 was transformed into the corresponding acetylenic phosphonium salt 10 , which was catalytically hydrogenated to the olefinic Wittig salt. Wittig olefination led, then, to the (6Z, 8Z)- and (4Z, 6Z, 8Z)-isomers, 7 and 8 , respectively. In a second approach, Friedel-Crafts reaction of 3-methylpent-l-en-4-yn-3-ol with the 2,3,5-trimethylanisol gave a C₁₅-intermediate with a terminal C?C bond in the side chain. After deprotonation and reaction with a C₅ aldehyd, the corresponding C₂₀-intermediate could be isolated in high yield. Finally, further conversion led predominantly to the (all-E)-retinoid, accompanied by its (9Z)- and (13Z)-isomers.     

Zum Mechanismus der Umlagerung von N-Aryl-S,S-dimethylsulfimiden zu o-Methylthiomethylanilinen

Zusammenfassung N-Aryl-S,S-dimethylsulfimide können entweder in aprotischen Lösungsmitteln in Gegenwart von Basen (Triäthylamin) oder in protischen Lösungsmitteln (Alkohole, Wasser) ohne Zusatz von Basen in o-Methylthiomethylaniline umgelagert werden. Die Geschwindigkeit der Umlagerung wird bestimmt von der Abspaltung eines Protons aus einer S-Methylgruppe und von der Lage des Gleichgewichts für die Protonierung am Stickstoffatom, was aus einem kinetischen Isotopeneffekt und aus der Richtung des Einflusses von p-Substituenten geschlossen wurde. Die eigentliche Umlagerung des intermediären S-Ylids ist rascher als seine Reprotonierung durch protische Lösungsmittel und entspricht einer sigmatropen [2,3]-Verschiebung.

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On the mechanism of the rearrangement of N-Aryl-S,S,-dimethyl sulfimides to o-methylthiomethyl anilines

N-Aryl-S,S-dimethyl sulfimides may be rearranged to yield o-methylthiomethyl anilines either in aprotic solvents in presence of bases (triethyl amine) or in protic solvents (alcohols, water) without addition of base. The rate of the rearrangement is determined by the rate of proton abstraction from one of the S-methyl groups as well as by the position of the equilibrium for protomation of the nitrogen atom, as indicated by kinetic isotope effects and the influence of p-substituents, respectively. The rearrangement of the intermediate S-ylide is faster than its reprotonation by protic solvents and represents a sigmatropic [2.3]-migration.

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Mit 4 Abbildungen

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Herrn Prof. Dr.O. Kratky zum 70. Geburtstag gewidmet.

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7. Mitt.:P. Claus, W. Vycudilik undW. Rieder, Mh. Chem.102, 1571 (1971).

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Teile der Ergebnisse über die Umlagerung des N-4-Chlorphenyl-S,S-dimethylsulfimids sind in der DissertationW. Rieder, Univ. Wien (1971), enthalten.     

Die photosensibilisierte Oxydation einwertiger Phenole zu Chinonen

The photosensitized oxidation of methyl substituted phenols with free para-positions starts with an electrophilic attack of position 4 by singlet oxygen. This follows from the course of the reaction using phenols with methyl groups in different positions. The influence of the solvent shows that the hydroperoxide formation from the primary oxygen adduct proceeds via an inter-molecular hydrogen shift. The solvent is the hydrogen donator, whereas the phenoxy radicals resulting from the oxidation of the phenol by the excited sensitizer are the hydrogen acceptors. Finally, the quinones are formed from the hydroperoxides by elimination of water.     

Die basenkatalysierte Umlagerung von N-Aryl-S,S-dialkylsulfimiden zu o-Alkylthioalkylanilinen

Zusammenfassung Die Umlagerung von N-Aryl-S,S-dimethylsulfimiden in Toluol/Triäthylamin liefert in hohen Ausbeuten o-Methylthiomethylaniline. In Alkohol verläuft die Umlagerung ohne Zusatz von Basen rascher, als Nebenreaktion läuft aber die Spaltung zu dem zugrunde liegenden aromatischen Amin ab. 2,6-Di-substituierte N-Arylsulfimide ergeben durch analoge Umlagerung Cyclohexadienimine. Die Umlagerung von N-Aryl-S,S-dialkylsulfimiden erfolgt langsamer als die der S-Methylderivate; sie führte in einem Fall in hohen Ausbeuten zu einem durch 1,2-Wanderung entstandenen N-Alkylthioalkylprodukt. Die Ergebnisse liefern Aufschlüsse über den Mechanismus von Methylthiomethylierungen von anilinen und Phenolen.

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Methylthiomethylation of anilines and phenols, VII: Basecatalysed rearrangement of N-aryl-S.S-dialkyl sulfimides to o-methylthiomethyl anilines

Rearrangement of N-aryl-S.S-dimethyl sulfimides in toluene/triethyl amine yields high amounts of o-methylthiomethylated anilines. Rearrangement in ethanol without addition of base proceeds faster, but yields also the original aniline as by-product. 2.6-Di-substituted N-aryl sulfimides yielded on analogous rearrangement cyclohexadiene imines. The rearrangement of N-aryl-S.S-dialkyl sulfimides is slower than that of the S-methyl derivatives, and yielded in one case high amounts of N-alkylthioalkyl product formed via 1.2-migration. The results offer some informations on the mechanism of methylthiomethylations of anilines and phenols.

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Herrn Prof. Dr.H. Nowotny gewidmet.

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6. Mitt.:P. Claus, N. Vavra undP. Schilling, Mh. Chem.102, 1072 (1971).     

Photolactonisierung: Ein neuer synthetischer Zugang zu Makroliden

Photolactonization: A Novel Synthetic Entry to Macrolides o-Quinol acetates, hydroxyalkylated at C(6), are easily accessible from simple phenols by Wessely acetoxylation (preferentially catalyzed by BF₃). On UV irradiation (in the presence of an appropriate tertiary amine), they are smoothly converted to macrocyclic lactones. Subtle conditions have been elaborated to lead to high overall yields, and the scope of the conversion of phenols to macrolides has been elucidated.     

Säurekatalysierte Umlagerung von 9-Hydroxyfuranoeremophilanen zu Eremophilanlactonen

Acid-Catalyzed Rearrangement of 9-Hydroxyfuranoeremophilanes to Eremophilanlactones 9-Hydroxyfuranoeremophilanes 1–3 are the main components of freshly harvested rhizomes of P. hybridus (furanopetasin chemovar, Table, Fig. 1). They easily and quantitatively rearrange in the presence of traces of acid to give an epimeric mixture of 8-H-eremophilanlactones 4–6 (eremophilenolides, Table, Figs. 4 and 5). Besides subsequent oxidation (see 4 → 7 ), this is the most important reaction occuring during drying and storage of rhizomes of P. hybridus (Figs. 1 and 3). A reasonable mechanism of the rearrangement is presented, and spectroscopic structure elucidation of 8-H-eremophilanlactones is discussed.     

Chemie der α-Aminonitrile 1. Mitteilung Einleitung und Wege zu Uroporphyrinogen-octanitrilen

Chemistry of α-Aminonitriles I: Introduction and Pathways to Uroporphyrinogen-octanitriles. An introduction to experimental studies on the chemistry of α-aminonitriles potentially relevant to the problems of prebiotic chemistry is presented. The framework of conditions wherein the investigation is chosen to be carried out implies both molecular oxygen and - whenever feasible - water to be excluded from reaction conditions. This study focusses on 2-amino-2-propenenitrile ( 3 ) (Scheme 6) as central starting material of reaction sequences which aim at the nitrile forms of proteinogenic amino acids as well as at the aza forms of building blocks of biological cofactor molecules as their targets (Scheme 5). Schemes 13,16,23 as well as 25 and 26 summarize reaction sequences by which 3 is transformed within the defined framework of conditions into the thermodynamic (statistically controlled) mixture of the four isomeric uroperphyrinogen-octanitriles 57–60 . HPLC's of such mixtures document the dominance of the least symmetrical isomer whose constitutional pattern of peripheral substituents happens to be the one percent in all biological porphinoids. Preparative procedures for the synthesis of 3 (Scheme 9), the β,β-disubstituted pyrrol-nitriles 30,53 and 54 (Scheme 19) as well as the porphyrinogenoctakis(propionitrile) and-octakis(acetonitrile) 65 and 66 , respectively (Scheme 24) are given.