Über einige neue Bispirane

We have obtained four new bispirane systems in which both spiroatoms are vicinal atoms in cyclopropane or cyclobutane rings and in which the heterocyclic component has the basic structure of 1,4-dioxep-2-ene. We have shown that from two possibilities (bispiran, propellan) the general reaction leads only to a bispiran system. To the bispiran2 exhibiting the highest hyperchromism we ascribed the bispirocoplanar conformation (Fig. 1).

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Identification of amber and imitations by near infrared reflection spectroscopy

Imitations of amber have been prepared since a long time, but the number of imitations is increasing since modern polymers are available. At present, many imitations are based on a few synthetic polymers and even experts have some problems in distinguishing between real and falsed amber without destruction of the material. IR-Spectroscopy or pyrolysis combined with gas chromatography/mass spectrometry are very efficient methods in identifying amber and imitations but these methods need a sample preparation. By means of near infrared reflection spectroscopy it is possible to identify amber and imitations without any sample preparation in a short time. Optimization of the method and the application are discussed.     

Phenylimino-phosphorsäure-(diäthylamid)-chloride

Zusammenfassung Monomere Phosphinimine der allgemeinen Formel C₆H₅N= =PCl _n (NEt₂)_3-n (n=0,1,2) lassen sich (I) aus dimerem Phenylimino-phosphorsäure-trichlorid und Diäthylamin in Gegenwart eines Chlorwasserstoffakzeptors und (II) durch Reaktion der Phosphine PCl _n (NEt₂)_3-n mit Phenylazid darstellen. Die Phosphorane Et₂NPCl₄, (Et₂N)₂PCl₃ und (Et₂N)₃PBr₂ reagieren mit Anilin nicht zu Phenylimino-Verbindungen. Durch alkalische Hydrolyse von C₆H₅N=PCl(NEt₂)₂ entsteht das Phosphorsäure-bis[diäthylamino]-anilid. Die IR- und¹H- und³¹P-NMR-Spektren der Verbindungen werden mitgeteilt.

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Monomeric phosphinimines of the general formula C₆H₅N= =PCl _n (NEt₂)_3-n (n=0,1,2) are formed (I) from dimeric phenyliminophosphoricacid-trichloride and diethylamine in the presence of a HCl-acceptor and (II) by reacting the phosphines PCl _n (NEt₂)_3-n with phenylazide. The phosphoranes Et₂NPCl₄, (Et₂N)₂PCl₃ and (Et₂N)₃PBr₂ do not give the corresponding phenylimines with aniline. Alkaline hydrolysis of C₆H₅N= =PCl(NEt₂)₂ gives bis[diethylamino]-anilido-phosphinoxid. IR-,¹H- and³¹P-NMR-spectra are given.

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Classification of Poincaré duality algebras over the rationals

The Poincaré duality algebras over Q play a key role in the rational homotopy classification of closed manifolds [3]. In this paper we give a way of classifying general Poincaré duality algebras and then specialize to the case of algebras which are generated by some homogeneous component and show how the classification reduces to the linear classification of certain homogeneous polynomials and exterior forms.     

Aza-Claisen Rearrangement: Synthesis of 5′-branched 5′-aminothymidines

The syntheses of both diastereoisomers of 5′-ethyl-substituted thymidine dimers, the (5′R)- and (5′S)-configurated 33a and 33b respectively, in which the natural phosphodiester linkage is replaced by an amide group (C(3′)-CH₂CONH-CH(5′)(Et)), arc described. Their fully protected derivatives 35a and 35b , respectively, are suitable for incorporation into antisense oligonucleotides. Unexpectedly, an attempted Pd^II-catalysed aza-Claisen rearrangement of trichloroacetimidate 7 provided the diastereoisomerically pure cyclopropane derivative 17 , whose structure was confirmed by X-ray analysis.     

Copper—A “Modern” Bioelement

Copper is a bioessential element in biology with truly unique chemical characteristics in its two relevant oxidation states +I and +II. Significant progress has been made in recent years in the elucidation of the frequently surprising biochemistry of this trace element. Those advances were especially furthered through mutual stimulation involving results from biochemistry, molecular biology, and medicine on one hand and the synthesis as well as the structural and spectroscopic characterization of low molecular weight model complexes on the other. The most notable features of protein-bound active copper are its almost exclusive function in the metabolism of O₂ or N/O compounds (NO, N₂O) and its frequent association with oxidizing organic and inorganic radicals such as tyrosyl, semiquinones, superoxide, or nitrosyl. This unique biological role of copper can be rationalized given its chemical and assumed evolutionary background.     

IBX-mediated alpha-hydroxylation of alpha-alkynyl carbonyl systems. A convenient method for the synthesis of tertiary alcohols

[reaction: see text] IBX (o-iodoxybenzoic acid) is an excellent reagent for the alpha-hydroxylation of alpha-alkynyl carbonyl compounds without giving dehydrogenation products. The convenient procedure proves to be useful for the construction of a variety of tertiary alcohols (55-91%) under mildly acidic conditions.     

A Short Synthesis of (−)-Carbovir

(–)-Carbovir ((–)- 1 ) was synthesized via the cyclic carbonate 2 in four steps starting from enantiomerically enriched (–)-(S)-(cyclopent-2-enyl)methanol ((–)- 3 ).     

A novel MCR of isocyanates, aldehydes, and dienophiles

[reaction: see text] A novel one-pot procedure for the three-component coupling reaction of isocyanates, aldehydes, and dienophiles (IAD reaction) has been developed. Condensation of isocyanates and aldehydes and subsequent Diels-Alder reactions with electron-deficient dienophiles furnishes endo-selective amino-substituted cyclohexenes in good yield.     

Das amphotere Verhalten von Titan(IV)-chlorid in Phosphoroxychlorid

Zusammenfassung Konduktometrische und potentiometrische Titrationen zeigen, daß TiCl₄ in POCl₃ sowohl 2 Chloridionen aufnehmen als auch ein Chloridion abgeben kann. Die Existenz der Koordinationsformen [TiCl₆]^2–, [TiCl₅]^– _solv, (TiCl₄)_solv und [TiCl₃]⁺ _solv läßt sich nachweisen. Das Verhältnis von Donor-und Akzeptorstärke ist von der Konzentration abhängig; in verd. Lösungen ist TiCl₄ vor allem Donor, in konz. Lösungen Akzeptor.Mit 6 AbbildungenZugleich 21. Mitt. der Reihe: Das Solvosystem Phosphoroxychlorid.20. Mitt.:M. Baaz, V. Gutmann undL. Hübner, J. Inorg. Nucl. Chem., im Druck.