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Article Dans Une Revue Journal of Organic Chemistry Année : 2008

Trimerization Products of Trifluoroacetone: Critical Solvent Effect on Position and Kinetics of Anomeric Equilibria

Résumé

In the presence of bases, trifluoroacetone is known to trimerize leading to configurationally labile 6-methyl-2,4,6-tris(trifluoromethyl)tetrahydro 2H-pyran-2,4-diols 1a,b and 2a,b, structurally close to fluorinated carbohydrates. We report herein a complete study of their behavior in solution. The remarkable solvent effect on the two equilibria (1a double left right arrow 1b; 2a double left right arrow 2b) was rationalized using solvent basicity measures and polarity scales. Solvents of weak donor number were found to favor the diastereoisomers 1a and 2a, which were subsequently isolated. According to their X-ray analyses, they both possess a concave structure with 1,3-cis-diaxial hydroxyl groups. A complementary kinetic study illustrated that acidic conditions can drastically reduce the equilibration rate, allowing the use of a wide range of solvents. Finally, a reexamination of previously published trimerization conditions using sodium or magnesium amalgam revealed that, contrary to the suggestion by two independent reports, 1,3,5-tris(trifluoromethyl)cyclohexane-1,3,5-triol 3/4 was neither formed as the principal product in place of 1a,b and 2a,b nor could it be detected as a minor product.

Dates et versions

hal-01122153 , version 1 (03-03-2015)

Identifiants

Citer

Pierre-Loïc Saaidi, Mathieu Guyonnet, Erwann Jeanneau, Paul Fleurat-Lessard, Jens Hasserodt. Trimerization Products of Trifluoroacetone: Critical Solvent Effect on Position and Kinetics of Anomeric Equilibria. Journal of Organic Chemistry, 2008, 73 (4), pp.1209-1216. ⟨10.1021/jo701669p⟩. ⟨hal-01122153⟩
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