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Enantiopure Bulding Blocks from Sugars, Part XVI.

Solid-State Conformations of 2,6-cis- and 2,6-trans-Substituted Dihydro-Pyran-3-ones

Frieder W. Lichtenthaler, Stephan Rönninger, Hans J. Lindner, Stefan Immel, and Eckehard Cuny

Carb. Res. 1993, 249, 305-326.

2,6-Dihydropyran-3-ones carrying substituents at C-2 and C-6 in cis-arrangement invariably adopt conformations in which the ring oxygen and the carbon atom next to the carbonyl group are above and below, respectively, the plane formed by the other four carbon ring atoms, i.e. the 2HO or OH2 conformation. in the case of a trans-arrangement of 2,6-substituents, the geometry of the pyranoid ring falls into the BO,6<-> EO<-> 2HO or the inverse O,6B<-> OE<-> OH2 section of the conformational cycle, depending on the absolute configuration of the compound; for the two of the dihydropyranones, 4B and 6, a unique skew-boat (SBO,6) conformation, fixed between the BO,6 and EO geometries, was ascertained, which previously has only been observed for pyranoid enelactones.

© Copyright PD Dr. S. Immel