Syntheses a l'aide de sulfones : XXIII. Sur la selectivite de la synthese des sulfones Allyliques

The role of the palladium ligands on the yield and regioselectivity of the reaction of conjugated dienes with arenesulphinic acids (or of allylic acetates with sodium arenesulphinates) has been investigated. Arenesulphinic acids catalyse the isomerisation of allylic sulphones.     

Addition en catalyse redox d'halogenures benzyliques sur les doubles liaisons

Benzyl chloride is shown to add to olefins in DMF in the presence of CuCl/bipyridyl, CuCl/phenanthroline or FeCl₂. Addition of p-nitrobenzyl chloride takes place under milder conditions.     

Addition des thiols sur les cetones—II : Mecanisme de l'addition du propanethiol

Addition of propanethiol to cyclohexanone in aqueous ethanol involves two consecutive steps, both of them rate limiting. The first step is the addition of the thiol to the conjugate acid of the ketone, giving an instable intermediate hemithioketal. Another thiol molecule adds to this, giving the thioketal. From the rate expression the thiol addition rate constant to the cyclohexanone was calculated.     

Addition des thiols sur les cetones-IV : Effets de solvant sur l'addition du mercapto-2/ethanol

The addition of 2-mercaptoethanol to cyclohexanone, in all solvents investigated, consists of two steps; first, the formation of hemithioketal, second, that of oxathiolane and thioketal by two competitive reactions. In aqueous ethanol 50/50 v/v both steps are rate limiting. When the ethanol content of the solvent increases, the second step becomes more and more rate limiting. In 20% ethanol, the rate limiting step is the formation of hemithioketal. This last result explains why, in water, Jencks has observed a first order reaction with respect to the thiol.     

Analyse conformationnelle a l'aide de la notation des angles de torsion—IV: Interpretation et prevision du cours sterique de l'addition conjuguee d'anions sur les cyclopenten-2 ones

With the help of the torsion angle notation the steric course of anion conjugate addition to cyclo-pentenones can be interpreted or predicted, taking into account the maintenance of orbital overlap and the least amount of structural distortion during the reaction.     

Analyse conformationnelle a l'aide de la notation des angles de torsion—II: Controle conformationnel de l'ouverture de monoepoxydes de dienes cisoides et transoides s'effectuant avec deplacement allylique de l'olefine

Taking advantage of the torsion angle notation and using only the assumption of the maintenance of orbital overlap during the reaction it is possible to analyse and interpret the steric course of the 1,4-opening of cisoïd and transoïd diene monooxide incorporated in mono or polycyclic structures. The stereochemistry of the reverse reaction, corresponding to diene monoepoxide formation from a γ-bromo-α,β-unsaturated-cyclohexanol can also be predicted.     

Organocuivreux vinyliques : IX. Addition de derives organiques du cuivre sur l'acetylene

The addition of various alkylcopper derivatives to acetylene is described. The best reagents are lithium dialkylcuprates in ether which form Z-dialkenylcuprates. ω-Funtionalized dialkylcuprates also add cleanly to acetylene. The Z-dialkenylcuprates thus obtained are iodinated to afford stereospecifically Z-1-iodoalkenes.     

Experimentation du plan de synthese etabli avec l'aide de pascop: Synthese assistee par ordinateur de la phosphacarnegine-II

Synthesis planned for phosphacarnegine 1by the PASCOP procedure was executed. Although some pathways were not appropriate, two successful routes giving 1 in a yield of 15 and 4.5% respectively are described. Limitations of PASCOP are discussed.     

Addition regioselective d'enolates de cetones aux α-enones: Influence des facteurs steriques sur l'orientation et la reversibilite des reactions

Regio and stereochemistry in the addition of preformed magnesium and lithium ketone enolates (1 to 8) to α-enones (10 and 11) have been examined. When the substitution degree of the enolate is increased the formation of δ-diketone is favoured; nevertheless a good efficiency in the synthesis of the γ-ethylenic β-ketols (1-2 addition) is obtained via bromomagnesium enolates (EMgX) under kinetic conditions. Lithium enolate (ELi) and, chiefly magnesium enolates (E₂MgX) give preferentially the Michael addition. Reversibility from 1-2 to 1-4 addition is commonly observed but the stereochemistry, if any, of the diastereoisomeric δ-diLetones may be quite different when using EMgBr or E₂Mg as starting enolates.     

Action des halogenures d'alkylmagnesium sur les pyrones-2—VI : Etude de la regioselectivite de l'ion enolate intermediaire de la reaction

Grignard reagents normally react with 2H-pyrones to yield unsaturated ketols, dihydropyranols, dienones and 2H-pyrans. In some cases, products are obtained by attack on the most sterically crowded position of the enolate ion. Since steric hindrance is an unsatisfactory basis for predicting the reactivity, we have applied a theoretical study to this problem. The model used is based on an enlarged electronic delocalization in the transition state, and allows the interpretation of the regioselectivity of the reaction.