Dérivés C-Glycosyliques XXXI. Utilisation en chimie des sucres du synthon bromo-2-cyano-2-éthényle. Communication préliminaire

C-Glycosyl derivatives XXXI. Some uses in Carbohydrate Chemistry of the 2-bromo-2-cyano ethenyl synthon Sugars bearing the synthon 2-bromo-2-cyano-ethenyl, ? CαH?Cγ(Br)C?N, reacted with binucleophiles, gave rise to α, α, α, β or α, γ ring-forming reactions. C-glycosyl-dioxolanes, -aziridines, -dithianes, -pyrimidines, -furanes and -pyrazoles were so obtained. The stereochemical paths of some of these reactions are discussed.     

Décomposition du percarbonate de O,O-t-butyle et O-isopropényle en solution: Acétonylation des esters,acides et nitriles

The Free-Radical Decomposition of O,O-t-Butyl and O-Isopropenyl Peroxycarbonate in Solution: the Acetonylation of Esters, Acides and Nitriles The free-radical decomposition of O, O-t-butyl and O-isopropenyl peroxycarbonate in substratres possessing mobile H-atoms (S? H) consists mainly in an induced chain process leading to acetonylated derivatives of the solvent. Fairly good yields are obtained but teh acetonylation of functional substrates often gives mixtures of isomers. In the case of methyl acetate, the acetonylation occurs on the C-atoms adjacent to the carbonyl (acylox moiety) and to the O-atom (alkox moiety). However, the relative amounts of the isomeric products depend on the concentration of the peroxycarbonate solutions; at lowest concentration, methyl 4-oxopentanoate (acyloxy moiety) is obtained selectively. It is assumed that the free radicals issued from the solvent are able to abstract H-atoms of other molecules of solvent before adding to the double bond of the peroxycarbonate; the more the peroxycarbonate solution is diluted the more the transfers from the C-atom adjacent to the carbonyl to the radicals adjacent to the O-atom are favoured. In the case of methyl alkanoates, H-transfers from the α-C-atoms to β-radicals of teh acyloxy moiety may account for the orientation of the process. Owing to similar H-transfer processes, the acetonylation of functional esters, of acids and nitriles is selective in most cases.     

Dérivés de sucres à groupement gem-dihalogénoéthényle

Carbohydrate Derivatives Bearing a gem-Dihalogenoethenyl Group Treated with the appropriate Wittig reagent, aldehydosugar derivatives ( 1–13 ) led in good to excellent yields to the expected gem-difluoro, gem-chlorofluoro-and/or gem-dichloroenoses ( 14–29 ). Examples of their dibromo analogues had been previously described (see e.g. [1]) but the diiodo derivatives could not be isolated, The influence of the conditions on the yields is reported as well as spectroscopic properties (particularly the long-range ¹³C, ¹⁹F- and ¹H, ¹⁹F-coupling constants) of these new enoses.     

Etude par Résonance Magnétique Nucléaire de dérivés anthracéniques: II—Anisotropie magnétique du phényle et effets steriques

The peri effect induced by the phenyl group has been studied in the anthracene series by means of ¹H and ¹³C n.m.r. The chemical shifts of overcrowded protons can be explained by a combination of magnetic anisotropy and steric effects. Steric contributions amount to c. 25% of the phenyl induced shift at the peri position. Amongst published ring-current theories, only the model of Johnson and Bovey is capable of describing correctly the shielding region of the phenyl group. The unexpected shieldings and deshieldings, observed by ¹³C n.m.r. in the case of very hindered derivatives, is probably due to distortions of the anthracene skeleton.