Etude des reactions pericycliques sous pression—IV: Cyclodimerisation thermique de l'acroleine et de la methylvinylcetone

The thermal cyclodimerization of acrolein with methyl vinyl ketone gives selectively only one substituted dihydropyran. The rate is only slightly sensitive to the nature of the solvent; however a slight decrease of the reaction rate with increasing solvent polarity was observed. Effects of high pressure give strong support for a one-step mechanism and the formation of a transition state more compact than the adduct.     

Synthese de derives de la tobrosamine par addition d'acide hydrazoique sur un systeme enonique dans la serie hydrate de carbone

Derivatives of a new diaminotrideoxy-d-ribo-hexopyranose, a component of the antibiotic tobramycin, have been prepared by addition of the elements of hydrazoic acid to the α, β-unsaturated ketone 8. After 5 min only the kinetically favored product 13 was observed, which is gradually transformed into the thermodynamically more-stable substance 20. The equilibrium mixture after 5 hours contained d-erythro and d-threo isomers 20 and 13 in the ratio 6:4 The d-erythro azide 20 was converted into the derivatives of di-N-acetyl tobrosamine.     

Étude par spectroscopie infrarouge de la structure du cation mg(h2o)62+ dans quelques sels de magnésium hydratés

The infrared spectra of eight hexahydrated magnesium salts have been investigated in the 4000-2000 cm^?1 range. The stretching H₂O, D₂O and HDO water bands are discussed. Two types of hydrogen bond depending on the acceptor properties of the anion can be distinguished: the water molecules are bonded to anions or to other water molecules.     

Synthese de tetrahydrodibenzofurannes : creation d'un carbone quaternaire par transposition de claisen.

A new route to tetrahydrodibenzofurannes is described. It is based upon Claisen transposition of an aryloxycyclohexene to $\text{o}$.hydroxyphenyl cyclohexene which is, in turn, cyclized by palladium acetate. In the studied example, an overall yield of 45 % is obtained in two steps. The isolation of an unexpected minor isomeric transposed compound sets a problem of mechanism.     

Synthese totale d'un analogue azote d'endoperoxyde de prostaglandine

The total synthesis of a prostaglandin endoperoxyde analogue in which the upper side chain is attached to a nitrogen atom, is presented.     

Etude d'un schema de synthese peptidique intramoleculaire a l'aide de derives du phosphore tetraedrique

A new scheme of repetitive and controlled peptide synthesis offers two advantages compared to the usual methods of synthesis : two steps only are used for the prolongation of a peptide chain with an aminoacid residue and the risk of racemisation is minimized. The two postulated steps are verified particularly by the rearrangement, in an alkaline alcoholic medium, of phosphordiamides 1 incorporating one amino-acid residue, leading to the formation of the peptide derivatives 6 and 8. The severe limitations of this method are discussed.     

Solvolyse d'un nouveau systeme homoallylique: les derives de cyclopropylidene-3 propyle

The solvolysis of 3-cyclopropylidene propyl derivatives can involve a participation of the double bond leading to the formation of a new three membered ring.     

Synthese d'oligonucleotides lies de facon covalente a un support solide

A method for the preparation of unprotected oligonucleotides, which remain anchored by a covalent linkage to a solid support, is described. Synthesis of several sequences up to a 18-mer by the phosphotriester method is reported.     

Influence d'un ou de plusieurs groupements tertiobutyle sur le comportement magnétooptique du doublet libre d'un atome de phosphore tricoordonné

A magnetooptical study of some halogenotertiobutylphosphines is performed in order to improve the so-called regular relationship which seemed to exist between the magnetic rotation, ?dP, of the lone pair and the bond angles in PX₃ compounds. It is clearly shown that, in any case, ?dP is largely lower than the extreme value which was observed in PX₃ molecules for which XPX=100°. Thus, the existence of the previously invoked relationship vanishes and the question remains as to why there exists a maximum of ?dP for XPX of 100°.     

Synthese et proprietes d'oligomeres presentant un nombre variable de fonctions acides

Materials with various contents of grafted acid groups have been prepared by radical addition of thiols to the double bonds in polybutadiene. For their determination, a method involving NMR and determination of $\text{Mn}$ is prepared. The glass transition temperature increases with the content of grafted acid groups. Intermolecular hydrogen bonds have been found by i.r. and viscosity studies. Relations between the ratio of free to bonded carbonyl groups and temperature and between log η₀ and (temp.)^?1 are linear for all samples with a change of slope between 120° and 140°C. This effect is found also for non-functional samples of polybutadiene; it is discussed in terms of the liquid-liquid transition T₁₁ and it is probably due to change in chain conformation.     

Oxydes d'allenes VI (1). migration-1,4 de fonction lors de l'oxydation selective de derives d'alcools α-alleniques. Synthese de dienones conjuguees.

The oxydation of α-allenic acetates affords conjugated dienones whereas α-allenic trimethylsilyl ethers give rise to silyl ethers of unsaturated α-cetols. A ?1,4 migration of the function is involved.     

Synthese d'un isostere soufre de la prostaglandine A2

The synthesis of the title compound $\text{2a}$, a prostaglandin with a β-thiolactone ring is described, which involves the use of 2-tetrahydropyranthiol, an efficient reagent for introducing the sulfur atom.     

Synthese de polymeres porteurs d'un antivitamine k, la phenindione

Synthesis of methacryl monomeric derivative of phenindione (vitamin k antagonist) has been achieved. These new monomers, characterized by NMR and i.r., have been polymerized by a radical process. Resulting homopolymers have been analysed and compared with polymers bearing phenindione, previously synthesized by chemical modification.     

Regio et stereochimie de la reduction de derives d'alcools propargyliques catalysee par un complexe de palladium (O)

Regio and stereoselectivity of the palladium catalyzed reduction of propargylic halides and esters is greatly influenced by the nature of the hydride donor as by the leaving group. Best results in allene formation are observed in the reduction by lithium triethyl-borohydride of mesylates and phosphates. In the former case, reaction occurs with anti displacement of the sulfonyl group.