Alain Botrel

Highly regio- and stereoselective reductions of carbonyl compounds in aqueous glycosidic media

Highly regioselective reductions of ct,13-unsaturated ketones to the corresponding allylic alcohols were performed in essentially quantitative yields in aqueous media containing either glycosidic surfactants or amphiphilic carbohydrates. Reductions of cyclohexanones and cyclohexenones lead under the same conditions, stereoselectively to reduced compounds bearing an equatorial alcohol function. Hydrophobic interactions between amphiphilic carbohydrates and lipophilic substrates were modelized and should account for the observed stereodifferentiation. Organic synthesis in aqueous media has attracted growing attention in the past few years.1 Unfortunately only a few organic compounds display sufficient solubility in water. The use of glyco-organic substrates, which contain a carbohydrate moiety enhancing water solubility and inducing chirality, was thus extensively studied. 1 However easy cleavage of the sugar moiety is a requisite for obtaining the final product. Alternatively, incorporation of the substrate and/or reagent molecules into micelles, microemulsions and various organized assemblies may enlarge the field of organic aqueous reactions. 2 Indeed, micellar aqueous solutions of surfactants proved recently to enhance both the rate and the enantioselectivity of asymmetric hydrogenations promoted by water-soluble rhodium catalysts based on carbohydrates. 20 In this paper, we would like to report on highly regio- and stereoselective reductions of a wide range of carbonyl compounds by sodium borohydride in aqueous solutions containing glycosidic amphiphiles. Our results will be compared with other findings based on the water structure strengthening effects exerted by sugars such as D-glucose. 3

An experimental and theoretical investigation of the regioselective cleavage of aromatic sulfones

Aromatic sulfones activated by strongly electron-withdrawing groups were reduced electrochemically. The radical anions produced were shown to be fairly stable. Cleavage reactions are so slow that other chemical reactions (protonation, dimerization, etc.) may take place. A theoretical study at the B3LYP level underlines that bond cleavage does not depend on the presence or not of electron-withdrawing groups substituted on the phenyl ring in the para position.

Intramolecular charge transfer in 5-phenyl-3H-1,2-dithiole-3-thione and 5-phenyl-3H-1,2-dithiole-3-one derivative molecules for quadratic nonlinear optics

SummaryThis paper deals with the theoretical and experimental studies of new sulfur-containing NLO chromophores: 5-phenyl-3H-1,2-dithiole-3-thione and 5-phenyl-3H-1,2-dithiole-3-one derivatives; ground-state and first1(ππ*) excited states characteristics are determined within the framework of MNDO-PM3 and CNDO/S-CI methods. These results are confronted with the NLO response of these molecules. The intramolecular charge transfer is identified and its contribution to the quadratic nonlinear susceptibility estimated and shown to be the main feature. Theoretical and experimental solvent effects on π → π* absorption bands are discussed. MNDO-PM3 finite-field first-order hyperpolarizabilities are compared to EFISH measurements. A preliminary CNDO/S parametrization of the sulfur atom in thio-carbonyl compounds is proposed and shown to be adequate for the description of electronic spectra.

Vectorial and Octupolar Components of the First-Order Hyperpolarizability in Push-Pull Benzopyranic Series

Vectorial (weight 1) and octupolar (weight 3) components of the first-order hyperpolarizability are computed using the PM3/RHF/FF method following two different decomposition schemes. These calculations evidence the importance of the weight 3 component of the β tensor even in push-pull molecules. The β values, output from the two decomposition schemes, are different but show the same evolutionary trend within benzopyranic molecule series. The square root of a macroscopic square average quantity 〈β,〉2)1/2 (which is usually determined in elastic second-harmonic light scattering experiment) is then computed and compared to the norm of the molecular β cartesian tensor.

Theoretical and experimental studies of electronic effects and second-order nonlinear optical properties of some benzenecarbothioates and benzenecarbodithioates

The relative nonlinear efficiency of some conjugated ester, thioester and dithioester molecules was investigated by quantum chemical semi-empirical methods. The results of calculations on ground and excited states properties and on “finite-field” hyperpolarizabilities β allowed to select the best compounds for quadratic nonlinear optics. Some of these molecules were synthesized and the theoretical results were confronted with the experimental NLO response obtained by β EFISH measurements. It was concluded from this analysis that the dithioester substituent represents an interesting electron-accepting group for applications in nonlinear optics and can be used instead of the nitro group.