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The relative rate constats of succeesive H/D exchange at carbons next to sulfur for the four alpha -methylene hydrogens in thiacyclohexylmethylsulfonium iodide (3) and thiacyclopentylmethylsulfonium iodide (2) with sodium deuterixide in D2O have been measured. The reactivity ratio for the two pairs of diastereotopic hydrogens in the six-membered ring (3) is near 1: 1, but in the five-membered ring (2) it is ca. 12: 1. The corresponding ratio for the two diastereomeric 2-methylthiacyclohexylmethylsullonium salts 4 and 5 at the methylene carbon is about the same as for the parent compound 3. The results for the thiacyclohexyl compound 3 agree with those found by others but those for the thlacyclopentyl compound 2 are onl~ in qualitative agreement, the selectivity being less by a factor of over 30 than reported earlier. The findings are discussed in relation to the present status of the gauche effect.

Etude de la diastereoselectivite des reactions d'acyl ou aroyl-2 trimethyl-4,4,6- ou -4,6,6 oxathiannes-1,3 avec des organometalliques (RMgX, R 2 Mg ou RLi) en fonction des variables suivantes: substitution (4,6,6 ou 4,4,6), nature du groupe acyl-2, nature de l'organometallique et de l'halogene dans le cas de RMgX, solvant, temperature; conditions optimales d'obtention d'un diastereoisomere

In stark saurem Medium an PtO2 und bei langerer Hydrierungszeit (30-130 Std.) erfolgt selektive Reduktion der Chinoline (I) bzw. von Isochinolin (III) zu den Tetrahydroderivaten (II) bzw. (IV).

On etudie les produits de methanolyse et de trifluoroethanolyse ainsi que les vitesses de methanolyse d'un certain nombre de p-toluenesulfonates d'alkylthio-3 et d'arylthio-3 propyle substitues sur la chaine

Four-component equilibria in substituted 1,3-dioxanes were applied to the determination of conformational energies not accessible by conventional equilibration, with the following conclusions: 1. The difference in free energy between the chair and twist forms of 2,2, trans - 4,6 - tetramethyl - 1,3 -dioxane is 7·4 kcal/mol. 2. Equatorial Me substituents at C-4,6 exert a palpable buttressing effect on the corresponding axial substituents. 3. Equatorial substituents at C-2 exert a similar buttressing effect on the geminal axial substituent. 4. The effect of equatorial t-Bu substitution or gem -dimethyl substitution at C-5 on conformational energy seems to be of minor importance. The more complex effects of equatorial 4-t-Bu substitution are discussed.

The structures of the title compounds I, II and III have been determined by X-ray crystallography. All three compounds, including the 8β-t-butyl isomer II(axial t-butyl), exist in double chair forms. Compound II is deformed by an outward tilt as well as a substantial twist (16.2°) of the t-butyl group away from the staggered conformation. A slightly lesser twist of 13.7° is found in the equatorial t-butyl isomer I. Outward bending of the axial N-methyl group also occurs in compound III.