Solid-state conformations of 2,6-cis- and 2,6-trans-substituted dihydropyran-3-ones

Article abstract of DOI:10.1016/0008-6215(93)84097-P

2,6-Dihydropyran-3-ones carrying substituents at C-2 and C-6 in cis-arrangement invariably adopt half-chair 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 atoms, i.e., 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<*>²H₆ or the inverse ^o,6B<*>^oE<*>^oH₂ section of the conformational cycle, depending on the absolute configuration of the compound; for 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.