Borane-catalyzed hydroboration of substituted alkenes by lithium borohydride or sodium borohydride

In the presence of a catalytic amount of BH₃·Me₂S, TiCl₄ or Me₃SiCl, LiBH₄ or NaBH₄ are capable of hydroborating alkenes by following the unusual order of decreasing reactivity: tetramethylethylene > 1-methylcyclohexene > cyclohexene; the key step of the catalytic cycle is the exchange reaction between LiBH₄ and the mono- or dialkylboranes resulting from hydroboration of the more substituted alkenes with BH₃.     

A rapid access to chiral alkylidene cyclopentenone prostaglandins involving ring-closing metathesis reaction

A synthesis of the alkylidene cyclopentenone prostaglandin TEI 9826 has been realized. The synthesis involved the preparation of the chiral 1,5-diene 8 using a stereoselective Claisen rearrangement from the allylic alcohol 6 giving the ester 7 after vinylation. Then a key RCM reaction allowed the preparation of the cyclopentenol 9 which, after oxidation, gave the cyclopentenone 10, precursor of the prostaglandin.     

Synthesis, characterization and crystal structures of two polyphilic mesogenic compounds

Three homologous series of semi-perfluorinated liquid crystals: 4-(2,2,3,3,4,4,4-heptafluoro-butyloxycarbonyl)phenyl, 4-(2,2,3,3,4,4,5,5-octafluoropentyloxycarbonyl)phenyl and 4-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyloxycarbonyl)phenyl 4-[(n-perfluoroalkyl)alkyloxy]benzoates have been synthesized. Their mesomorphic properties were studied by DSC, microscopic observation and X-ray diffraction. Their layer spacings are smaller than the molecular length (L). The ratio d_SA/L is about 0.7. The crystal structure of two derivatives of the first family have also been investigated. In both structures the molecules pack in smectic C-like sheets where neighbouring molecules are antiparallel, interacting through dipolar and van der Waals forces. The interactions between contiguous sheets, through the ends of perfluorinated chains are very weak. The X-ray diffraction results on the mesophases and on the crystalline structures of two compounds of the first family are compared. From this, we propose a model of the smectic phases with a zig-zag structure.     

CHEMILUMINESCENCE AND ENERGY TRANSFER FROM SINGLET OXYGEN PAIRS

Abstract— Chemiluminescence and photochemiluminescence of systems generating excited (singlet) molecular oxygen has been studied at low temperature in fluid media. A possible interpretation is proposed: that dimers of singlet oxygen are directly or indirectly responsible for the observed emission, the species [¹δg +¹σg⁺] predominating. Energy transfer to a fluorescent molecule is possible only when conditions of spectral overlap, required for transfer by inductive resonance, are fulfilled. Evidence is also presented for the formation of a transient complex between oxygen and a sensitiser or acceptor molecule [S…O₂], which is the precursor of singlet oxygen in these systems. However, other possible mechanisms cannot be excluded.     

Taking advantage of luminescent lanthanide ions

Lanthanide ions possess fascinating optical properties and their discovery, first industrial uses and present high technological applications are largely governed by their interaction with light. Lighting devices (economical luminescent lamps, light emitting diodes), television and computer displays, optical fibres, optical amplifiers, lasers, as well as responsive luminescent stains for biomedical analysis, medical diagnosis, and cell imaging rely heavily on lanthanide ions. This critical review has been tailored for a broad audience of chemists, biochemists and materials scientists; the basics of lanthanide photophysics are highlighted together with the synthetic strategies used to insert these ions into mono- and polymetallic molecular edifices. Recent advances in NIR-emitting materials, including liquid crystals, and in the control of luminescent properties in polymetallic assemblies are also presented. (210 references.).     

Action d'organolithiens sur la méthyl-2 quinoxaline. Etude de la réactivité des adduits

The action of organolithium reagents such as phenyllithium or n-bulyllithium on 2-methylquinoxaline gave lithiation of the methyl group which upon reaction with electtropholesphiles produce side chain alkenyl derivatives. On the other hand organolithium reagents react with the quinoxaline azomethine bond to give I-lithio-2-alkyl)or ary-1)-3 methylquinoxalines which can be further loithiated on the methyl group to give 2-alkyl(or aryl)-3-alkenylquinoxaline derivatives. The adducts can be condensed with clectrophiles such as benzonitrile or methlyl benzoate but only methyl benzoate leads to N condensed derivatives. Furthermore substituted 1,2,3,4-terahydroqinoxalines are available via the above lithio intermediates.     

Crystallographic evidence of hexacoordination at phosphorus via intramolecular coordination of donor groups on phosphane and phosphane sulphide

The X-ray structure analysis of bis(8-dimethylamino-l-naphthyl)phenylphosphane (3) and of the corresponding sulphide 4 has revealed hexacoordination at phosphorus in both cases, the N … P separations being less than the sum of the van der Waal radii. Furthermore, in both cases the overall geometry corresponds to a distorted bicapped tetrahedron. The optimum geometry calculated for 4 via the program developed by Autodesk (MM + method) suggests that the structure of the molecule is a function not only of steric requirements but also of electronic effects.     

Etudes stéréochimiques XIV. Adduits de Diels-Alder en série résiniques; action des peracides et ouvertures acido-catalysées d'époxydes

Studies in Stereochemistry XIV. Diels-Alder adducts in the resin series; action of peracids and acid-catalysed ring opening of epoxides The synthesis of Diels-Alder compounds of type 2 with a 17-nor-13(14)-atisène skeleton is described (cf. Schemes 1–3). Depending on the nature and configuration of substituents R¹ and R² on the carbon atoms 15 and 16, an epoxide ( 24–33 ) or a ketone ( 35–38 ) or a mixture of epoxide, ketone and lactone is obtained by the action of p-nitroperbenzoic acid on the double bond of these adducts (cf. Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid-catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (e.g. 52 ) or hydroxy-γ-lactones of (13R*, 14S*)-configuration (e.g. 50 ) resulting from the opening of the epoxide ring with retention of configuration were obtained.     

Une nouvelle methoxylation d'hydroperoxy-3 indolines issues de la photo-oxygenation d'indoles en milieu reducteur

3-Hydroperoxy-1,3,6-trimethyl-2-phenyl indolines coming from the sensitized photooxygenation of the indoles in presence of KBH₄ rearrange partially in basic methanol into the corresponding 3-hydroxy-6-methoxymethyL indolines.     

Syntheses d'oxazolidines substituees par l'adamantane et de nitroxydes oxazolidines stables derives de l'adamantane

Adamantane oxazolidine derivatives have been prepared. The corresponding mono and biradicals have molecular shapes well suited to the study of the motion anisotropy in solution.