Vinylallenes IX. - preparation de quelques tetraenes-1,2,4,6

The title hydrocarbons have been obtained by the reaction of Grignard reagents with derivatives of 4,6-diene-2-yne-1-ols in the presence of cuprous bromide.     

Heterocycles Contenant du Phosphore—V. Analyse des Spectres de Resonance Magnetique Protonique des Oxo-2 Methoxy ou Phénoxy-2, Methyl-3, Oxazaphospholanes-1,3,2: Exemples de Spectres du type ABXY

The ³¹P decoupled PMR spectra of the title oxazaphospholanes give rise to well resolved ABXY patterns. Among the eight possible solutions, six can be readily eliminated from chemical shifts considerations and the choice between the remaining two is based on tickling experiments. Good fits are observed between experimental and calculated spectra. The relative signs of the ³J(P? O? C? H) and ³J(P? N? C? H) coupling constants are given by tickling and Indor experiments. The ring conformation is discussed.     

Synthese der (3S,4R,3′S,4′R)- und (3S,4S,3′S,4′S)Crustaxanthine sowie weiterer Verbindungen mit 3,4-Dihydroxy-β-Endgruppen

Synthesis of (3S,4R,3′S,4′R)- and (3S,4S,3′S,4′S)-Crustaxanthins and Further Compounds with 3,4-Dihydroxy β-End-groups Starting from 3 , the enantiomerically pure title compounds were synthesized in eight steps. Spectra and HPLC systems are presented that allow a distinction between these isomers.     

Etude structurale d'un pyrochlore non stoechiométrique et désordonné contenant Bi(III) et Bi(V)

The formula of the compound [K_1.14Bi^III_0.37] [Bi^III_0.27Bi^V_1.73] [O_4.9OH_1.1]OH_0.8 has been established by means of analytical methods and least-squares refinement of the structure based upon X-ray powder diffraction data. This nonstoichiometric pyrochlore-type compound (a = 10.965(1) Å) is highly disordered: A fraction of the 16d positions of S.G. Fd3m is occupied by K⁺ and Bi³⁺ ions and a fraction of the 48 f positions by O^2? and OH^? ions; furthermore, octahedral sites are shown to accommodate both Bi³⁺ and Bi⁵⁺ ions. It is suggested that the use of 32e (rather than 8b) positions for anions can account for an upper limit of the 16d positions occupancy factor.     

Intermediaires organiques du germanium divalent: III obtention de germylenes γ-hydroxyles à partir de 3-chlorohydrogermyl-1-propanols et de 3-methoxyhydrogermyl-1-propanols

3-chlorohydrogermyl-1-propanols ClH₂Ge(CH₂)₃OH and Cl₂HGe (CH₂)₃OH are synthesized by action of mercury (II) chloride, in tetrahydrofuran, on 3-germyl-1-propanol H₃Ge(CH₂)₃OH. By thermal effect these halohydrides released hydrochloric acid, with formation of oxagermacyclopentanes (R = H or Cl); these derivatives decomposed by α-elimination with formation of γ-hydroxy divalent species of germanium RGe(CH₂CH₂)₃ OH (R = H or Cl). ‘Chlorine-methoxy’ exchange using tributylmethoxygermane on Cl₂HGe(CH₂)₃OH leads to the 3-methoxyhydrogermyl-1-propanols (MeO)ClHGe(CH₂)₃OH and (MeO)₂HGe(CH₂)₃OH; α-decomposition on the germanium atom in these latter compounds leads to the formation of the same γ-hydroxypropylgermylenes. These functional divalent germanium species were characterized by insertion into some σ-bonds.     

Sterospecific synthesis of 1,2-difluoroethylenes

So far, no general and simple synthetic method was available to prepare 1,2-difluoroethylenes $\text{1}$ bearing only one hydrocarbon substituent.We developed such a method, using the steps outlined in the following sequence :

The alkenes $\text{1}$, whose configuration was always found to be Z could be epoxidized into cis 1,2-difluoroepoxydes.The different steps will be detailed and discussed.     

A new look at the brachistochrone problem

Summary The classic brachistochrone problem is solved as an optimal control problem in conjunction with the use of Chebyshev series.

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Résumé Le problème classique du brachistochrone est résolu comme un problème de contrôle optimale à l'aide des séries de Chebyshev.

     

Reactivity and selectivity of homolytic substitution reactions on the peroxyacid group

Peracids in solution may undergo homolytic decomposition leading mostly to mixtures of acid and alcohols, these Latters being formed from either the peracid or the solvent

The peracid behaves as source of radicals and also as substrate thus presenting two radicophile centers

- with a nucleophilic radical (R' from peracid or S' from solvent) the site of attack is the 0-0 bond of the peracid yielding an alcohol (NuOH). The rate of this reaction increases with increasing nucleophilicity of the radical ; this reactivity is interpreted in terms of frontier orbital perturbation theory, taking into account both the orbital energy level difference and the orbital overlap.- when the radical is electrophilic, it abstracts rather the hydrogen of the peroxidic group Leading to decomposition of the peracid into acid.Hydrogen abstraction from the solvent may be also observed in appropriate cases : this process can be used for free radical hydroxylation of hydrocarbons.The relative importance of these three chain reactions in competition : 0-0 bound attack, hydrogen abstraction from the peracid and solvent transfer reaction were studied as a function of structure of the radicals, solvent properties and temperature.