Methods for the preparation of three cyclic 2,3,4-tris(hydroxymethyl)-6-methylpyridin-5-ol acetonides have been developed by variation of the reaction conditions. The six-membered acetonide turned out to be thermodynamically more stable than the seven-membered acetonide and bis-acetonide. The experimental data were consistent with the results of quantum-chemical calculations. The structure of the isolated compounds was proved by X-ray analysis.Protection of glycols via transformations into cyclic acetonides is used more frequently than other protective groups [1-3] due to facile introduction of acetonide protection, stability of acetonides in neutral and alkaline media, and their lability under relatively mild conditions of acid hydrolysis. The formation, stability, and conformational specificity of cyclic acetals derived from pyridoxine attract both practical and considerable theoretical interest [4]. Pyridoxine can be converted into two cyclic six-and seven-membered acetonides, depending on the concentration of acid catalyst [5,6].At low concentration of hydrogen chloride or p-toluenesulfonic acid, kinetically controlled product is obtained, whereas at higher concentration of the acid catalyst the product is thermodynamically more stable six-membered acetonide.We previously developed a new and convenient procedure for the synthesis of 2,3,4-tris(hydroxymethyl)-6-methylpyridin-5-ol (I) [7]. Unlike pyridoxine, compound I could give rise to four cyclic acetonides: three monoacetonides II-IV and tricyclic bisacetonide V. We calculated the energies of formation
Attachment of 2-mercaptoethanol and thioglycolic acid methyl ester to the double bond of (1S)-(-)-b-pinene yielded pinane sulfides with the cis configuration. Oxidation of sulfides with m-chloroperbenzoic acid yielded the corresponding sulfoxides and sulfones. The resulting compounds were screened for antimycotic activity and the dynamics of changes in antifungal properties in sulfides-sulfoxide-sulfone series were studied.
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