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Article

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

Supporting Info

Pierre-Loïc Saaidi,^† Mathieu Guyonnet,^† Erwann Jeanneau,^‡ Paul Fleurat-Lessard,^† and Jens Hasserodt*^†

Laboratoire de Chimie, UMR CNRS 5182, Universit de Lyon-ENS, 46 Alle d'Italie, 69364 Lyon, France, and Centre de Diffractomtrie Henri Longchambon, Universit de Lyon-UCB, 43 bd du 11 Novembre 1918, 69622 Villeurbanne, France

J. Org. Chem., 2008, 73 (4), pp 1209–1216

DOI: 10.1021/jo701669p

Publication Date (Web): January 17, 2008

†

Université de Lyon-ENS.

‡

Université de Lyon-UCB.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, jens.hasserodt@ens-lyon.fr

Abstract

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 1b; 2a 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.