Voici les éléments 1 - 4 sur 4
  • Publication
    Accès libre
    Synthesis of Calix[4]pyrrolidine, Calix[m]tetrahydrofuran[n]pyrrolidine (m+n=4) and similar macrocyclic systems - elucidation of the hydrogenation sequence and factors influencing the stereoselectivity
    The first meso-octaalkylporphyrinogen (calix[4]pyrrole) was synthesized by Baeyer more than 120 years ago, mixing pyrrole and acetone in the presence of an acid. We have performed a thorough study of the catalytic hydrogenation of calix[4]pyrrole 1, by using common as well as novel heterogeneous catalysts based on transition metals (Pd, Rh, Ru) supported on solid matrices. Another investigation concerning the hydrogenation reaction was performed using twelve different macrocyclic substrates. Different factors were tested, which might influence the stereoselectivity during the hydrogenation process and therefore the number of diastereomers obtained. One of the macrocycles synthesized, offers interesting perspectives for the development of novel catalysts. In this context, we investigated the reactivity and the modification of this macrocycle. A thorough study of the nucleophilic properties and a kinetic study allow the discovery the factors that influence the reactivity of these macrocycles.
  • Publication
    Accès libre
    4,4-Bis(1H-pyrrol-2-yl)pentanol
    The title achiral compound, C13H18N2O, crystallized in the chiral monoclinic space group P21. The pyrrole rings are inclined to one another by 62.30 (11)°, and the propanol chain is in an extended conformation. In the crystal, the two pyrrole NH groups are involved in intermolecular N-H ··· O hydrogen bonds, leading to the formation of a helical arrangement propagating along the b axis. An interesting feature of the crystal structure is the absence of any conventional hydrogen bonds involving the hydroxy H atom. There is, however, a weak intermolecular O-H ··· π interaction involving one of the pyrrole rings.
  • Publication
    Accès libre
    Catalytic Hydrogenation of meso-Octamethylporphyrinogen (Calix[4]pyrrole)
    (2010) ;
    Letondor, Christophe
    ;
    ; ;
    Diego Savoia
    ;
    Andrea Gualandi
    Hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts under different experimental conditions has been investigated. GC-MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product derived from half-hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings, while the fourth was the all-cis saturated product. An acidic medium was necessary to achieve hydrogenation. However, the use of too strongly acidic solvents or additives was detrimental to the stability of the substrate and/or the catalyst.
  • Publication
    Accès libre
    2,2'-(Propane-2,2-diyl)bis(1H-pyrrole)
    The title compound, C11H14N2, crystallized with two independent molecules (A and B) in the asymmetric unit. The two molecules differ only slightly, with the pyrrole rings being inclined to one another at a dihedral angle of 87.67 (8)° in molecule A and 88.09 (7)° in molecule B. In the crystal, there are no classical hydrogen bonds, but the two pyrrole NH groups of one molecule are involved in N-H ··· π interactions with the pyrrole rings of the other molecule. In this manner, a compact box-like arrangement of the two independent molecules is formed.