Baylis-Hillman adducts in rhodium-catalyzed 1,4-additions: unusual reactivity

In the presence of a rhodium catalyst, unactivated Baylis-Hillman adducts reacted with arylboronic acids to afford trisubstituted alkenes with good yields. This highly efficient reaction (aerobic conditions, low temperature) is believed to proceeds via an unexpected mechanism involving 1,4-addition/beta-hydroxy elimination steps and not pi-allyl type rhodium intermediates.     

An Expeditious One-Pot Synthesis of N-Substituted 6-Nitroindoles from Indolines

Summary.  This paper reports an one-pot method for the concomitant alkylation – oxidation (aromatization) of indolines, particularly effective to get easy access to N-alkyl-6-nitroindoles, which are useful platforms in medicinal chemistry. N-alkyl-6-nitroindoles are obtained in good yield (64–91%) by reaction at room temperature in non-degassed DMF of 6-nitroindoline, an alkyl halide, and NaH as base. The presence of NaH appears to be essential for a high yield conversion. Corresponding author. E-mail: pdepreux@phare.univ-lille2.fr Received December 3, 2002; accepted December 9, 2002 Published online May 26, 2003     

Photoreactivite de l'ester de dieckmann α-methyle. Applications de la reaction du type I de norrish a la synthese du dihydroterpenediol secrete par danaus chrysippus et a celle des alcools du lilas

The α-methyl Dieckmann ester, when irradiated with UV light, gives a mixture of relatively light stable E and Z isomers of 5-carbethoxyhex-4-en-1-al 2, (77% yield). Although the 2E isomer can be isolated in pure form in almost 50% yield, separation of the two isomers is unnecessary. Their formation has been used as a key step in the total synthesis of the dihydroterpenediol 3 (34% overall yield) secreted by Danaus Chrysippus (African Monarch), and the four lilac alcohols 4.     

Caractérisation des longueurs de fibres dans différents types de composites polypropylène-fibres de verre courtes—2 partie. Etude des matériaux après injection

The aim of this work, dealing with injection moulding of short glass fibres reinforced-polypropylene matrix composites, was to investigate the interrelations which can exist between:

• •|some matrix and fibres-size composition and injection moulding parameters

• •|fibre length distributions in injection moulded test pieces

• •|associated mechanical characteristics.

We have shown that:

1. (1)|when the different unreinforced polypropylenes used as matrices have quite identical molten state viscosities, they have little influence on the glass lengths distributions in injection moulded pieces

2. (2)|on the opposite, the glass fibres size composition can exert a strong influence on fibres lengths distributions in injection moulded pieces: the incorporation of aminosilane + anhydridmaleic-polypropylene modified coupling agent in the fibres size always involves an increase of mean fibres lengths and a decrease of the fibres lengths scattering

3. (3)|the alteration of some injection parameters like screw speed, barrel temperature or back pressure level always involves expected changes of mean fibre lengths but:

• •|when the fibres are sized without coupling agent, a fibre length reduction is always associated with a decrease of mechanical characteristics

• •|on the opposite, when an aminosilane + anhydrid-maleic-polypropylene modified coupling agent is incorporated in the fibre size, the interrelation between mean fibre lengths and mechanical characteristics is far less clear. This phenomenon has been interpretated in terms of structural changes at the interface between polypropylene matrix and glass fibres.

     

Kinetic and thermodynamic consequences of the substitution of SMe for OMe substituents of cryptophane hosts on the binding of neutral and cationic guests

To investigate the origin of the high selectivity of cryptophane-E (1) towards Me3NH+, Me4N+, and CHCl3, and particularly to discriminate the different contributions that stabilize the supramolecular complexes, we have synthesized the new cryptophane 2 bearing six MeS groups instead of MeO groups in 1. This led to a decrease of the negative charge density in the equatorial region of 2 without affecting notably the size of the molecular cavity. The binding properties of 1 and 2 towards the three guests were examined in solution and showed a slight decrease of the deltaGa favoring the complexes of 1, accompanied by a significant modification of the deltaHa vs. deltaSa balance. The binding of the ammonium guests to 1 and 2 was strongly entropy driven, while that of CHCl3 was purely enthalpy driven. A combination of spectroscopic and computational techniques was used to assign the main intermolecular interactions that occurred during the inclusion process. The neutral CHCl3 molecule is more stabilized in the less negatively charged CTV cap of 1. The different behavior towards the ammonium cations can be explained in term of interactions with the electronegative heteroatoms and cation-pi interactions. Moreover, this study revealed a considerable slowing down of the guest exchange kinetics with host 2, for which the association and dissociation rates are reduced by a factor 10(3) to 10(4) with respect to 1. For example, at room temperature, the Me4N+@2 complex exhibits a half-life of ca. 2 years, instead of a few hours for the corresponding complex of 1.     

Fragmentation des δ-Dicetones,Analogies Avec le Comportement Photochimique

The mass spectra of thirty δ-diketones are reported. Their main pathways have been rationalized with the aid of deuterium labelling, metastable ions and high resolution mass measurements. Special attention has been given to ions resulting from the expulsion of neutral molecules such as water preceded, or followed by the loss of ethylene or alkenes. The expulsion may involve an intermediate cyclobutanol ion which would be analogous to the photochemical reaction observed by Yang.     

Generalite de l'effet structural d'un motif bitertiaire en rmn 13C: effet gem-6 de 6ème substitution methyle

In di-tertiary groups like (Me₃C)₂¹³C, the sixth methyl substituent $\text{inverts}$ or $\text{attenuates}$ the induced ¹³C chemical shift of sp² or sp³ sites (B_σ and y_π effects).     

Anhydrodihydroartemisinin and its 10-trifluoromethyl analogue: access to novel d-ring-contracted artemisinin trifluoromethyl ketones

The preparation of the 10-trifluoromethyl hydroartemisinin, followed by dehydration, afforded the trifluoromethyl analogue 2 of anhydrodihydroartemisinin 1. The reactivity of these two glycals of artemisinin were compared in epoxidation and halogenation reactions. Iodination of glycal 1 in water and the further rearrangement of the produced iodo hemiacetal provided the new D-ring-contracted aldehyde 8alpha, where the methyl at C-9 is beta. Epoxidation of 10-trifluoromethyl anhydrodihydroartemisinin 2 stereoselectively provided the beta-epoxy ether 11 in high yield. When treated with hexafluoro-2-propanol or trifluoroethanol, 11 readily underwent a rearrangement yielding to the D-ring-contracted trifluoromethyl ketone 9alpha with retention of configuration at C-9.     

Synthèse et caractérisation de bis acridines pontées en positions 2, 3 ou 4

The preparation of 2,2′, 3,3′ and 4,4′-bridged bisacridines is described. The method consists in the acylation of 2m 3, or 4-aminoacridines in acetone, as the solvent. Ten bisacridines were isolated and characterized by their ¹H and ¹³C nmr parameters. Some of these were tested as potential intercalating agents, but none has shown any activity from this point of view.     

Synthesis, structures, and magnetic properties of novel mononuclear, tetranuclear, and 1D chain Mn(III) complexes involving three related asymmetrical trianionic ligands

The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H(3)L(i) (i = 4-6). These ligands are obtained through reaction of salicylaldehyde with "half-units", the latter resulting from monocondensation of different diamines with phenylsalicylate,. Upon deprotonation, L(i) (i = 4-6) possess an inner N(2)O(2) coordination site with one amido, one imine, and two phenoxo functions, and an outer amido oxygen donor. The trianionic character of such ligands yields original neutral complexes with the L/Mn stoichiometry. The crystal and molecular structures of three complexes have been determined at 190 K (1) or 180 K (2 and 3). Complex 1 crystallizes in the triclinic space group P (No. 2): a = 7.8582(14) A, b = 10.9225(16) A, c = 12.4882(18) A, alpha = 67.231(14) degrees, beta = 72.134(14) degrees, gamma = 82.589(13) degrees, V = 940.6(3) A(3), Z = 2. Complex 2 crystallizes in the orthorhombic space group Pbcn (Nuomicron. 60): a = 23.8283(15) A, b = 11.1605(7) A, c = 26.152(2) A, V = 6954.8(8) A(3), Z = 8, while complex 3 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 11.7443(14) A, b = 7.5996(10) A, c = 18.029(2) A, beta = 100.604(10) degrees, V = 1581.6(3) A(3), Z = 4. Owing to hydrogen bonds and pi-pi stackings, the mononuclear neutral molecules of 1 are arranged in a 2D network while complexes 2 and 3 are tetranuclear and polymeric (1D chain) species, respectively, owing to the bridging ability of the oxygen atom of the amido function. The experimental magnetic susceptibilities of complexes 2 and 3 indicate the occurrence of similarly weak Mn(III)-Mn(III) antiferromagnetic interactions (J = -1.1 cm(-1)). Single ion zero-field splitting of manganese(III) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry in 2 (J = - 1.1 cm(-1), D(1) = 2.2 cm(-1), D(2) = -2.8 cm(-1)), D(1) and D(2) being associated to the six- and five-coordinate Mn ions, respectively. A weaker antiferromagnetic interaction (J = - 0.2 cm(-1)) operates through pi-pi stacking in complex 1. Complex 3 is a weak ferromagnet (ordering temperature approximately 7 K) as a result of the spin canting originating from the crystal packing.