TUD Organische Chemie

Immel

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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 ²H_O or ^OH₂ conformation. in the case of a trans-arrangement of 2,6-substituents, the geometry of the pyranoid ring falls into the B_O,6 E_O ²H_O 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 (SB_O,6) conformation, fixed between the B_O,6 and E_O geometries, was ascertained, which previously has only been observed for pyranoid enelactones.