Conformational analysis of some pyridinium phenolates and synthetic precursors based on X-Ray and IR characterisations

7 pagesInternational audienceThis manuscript reports X-Ray and IR characterizations of representative pyridinium phenolates, model compounds for nonlinear optics. These analyses reveal the close dependence existing between molecular structure and the contribution of quinone and zwitterionic limiting forms. The bond length alternation (BLA) values, the well-known parameter correlated to hyperpolarisability β, are also discussed and compared with literature data

Extended RCM–ROM sequences: a novel approach to polyunsaturated trisaccharides

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Ring-rearrangement metathesis of substituted dihydropyrans and dihydrofurans

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Soft Photopolymerizations Initiated by Dye-Sensitized Formation of NHC-Boryl Radicals under Visible Light

International audienceA procedure for the production of N-heterocyclic carbene boryl radicals (NHC-BH2 center dot) upon visible light irradiation under soft conditions is presented. New acridine orange (dye)/diphenyl disulfide/NHC-BH3 and dye/sulfonium salt/NHC-BH3 three-component initiating systems are introduced for the efficient visible light photopolymerization of trimethylolpropane triacrylate. The new systems could be extendend to polymerization reactions in water (hydroxyethyl acrylate and hydroxyethyl methyl acrylate), which proceeded with strongly improved polydispersity. The chemical mechanisms are investigated through EPR and photolysis experiments

On the Synthesis, Characterization and Reactivity of N-Heteroaryl-Boryl Radicals, a New Radical Class Based on Five-Membered Ring Ligands

International audienceThe synthesis and physical characterization of a new class of N-heterocycle-boryl radicals is presented, based on five membered ring ligands with a N(sp(2)) complexation site. These pyrazole-boranes and pyrazaboles exhibit a low bond dissociation energy (BDE; BH) and accordingly excellent hydrogen transfer properties. Most importantly, a high modulation of the BDE(BH) by the fine tuning of the N-heterocyclic ligand was obtained in this series and could be correlated with the spin density on the boron atom of the corresponding radical. The reactivity of the latter for small molecule chemistry has been studied through the determination of several reaction rate constants corresponding to addition to alkenes and alkynes, addition to O-2, oxidation by iodonium salts and halogen abstraction from alkyl halides. Two selected applications of N-heterocycle-boryl radicals are also proposed herein, for radical polymerization and for radical dehalogenation reactions

Towards a green molecular chemistry

National audienceThe organic synthesis challenge is now to manage the demands for efficiency and selectivity with the development of a "green and sustainable" organic chemistry. The goals are to obtain complex molecular architectures by reducing the environmental impact, by developing atom- and step-economic new methodologies, and by developing smart alternatives to usual organic solvents