(1S,2S,6R,7aR)-2-Benzyl-1,6-dihy-droxy-hexa-hydro-pyrrolizin-3-one

(1S,2E,6R,7aR)-1,6-Dihy-droxy-2-(4-nitro-benzyl-idene)-2,3,5,6,7,7a-hexa-hydro-1H-pyrrolizin-3-one

The crystal structure of the title compound, C₁₄H₁₄N₂O₅, contains two distinct conformers in the asymmetric unit. The compound has three defined stereocenters, two of them contiguous, and a C=C double bond with an E conformation. The stereocenters exhibit the same chirality in both conformers, with significant differences in the conformation of the five-membered rings of the pyrrolizine unit (both either in a twist or in an envelope form) and in the dihedral angles between the corresponding mean planes and the benzene rings. A prominent feature is a change from almost coplanar rings in one conformer to a new conformation in the second conformer, in which the mean plane of a five-membered ring is almost perpendicular to the benzene ring, with a dihedral angle 87.19 (8)°; the corresponding angle in the first conformer is 14.02 (10)°. In the crystal, molecules are linked by O—H⋯O and C—H⋯O hydrogen bonds. Crystallographic data were essential to confirm the configuration of the double bond, which was unclear from the available two-dimensional NMR data. In addition, reliable Flack and Hooft parameters were obtained, allowing for the correct absolute structure to be determined.

(1S,2E,6R,7aR)-2-Benzyl-idene-1,6-dihy-droxy-2,3,5,6,7,7a-hexa-hydro-1H-pyrrolizin-3-one

In the title compound, C₁₄H₁₅NO₃, the conformation of the double bond was determined to be E, confirming the result obtained from two-dimensional NMR data. The five-membered rings of the pyrrolizine unit exhibit C-envelope conformations, with C atoms displaced from the mean planes formed by the remaining rings atoms by 0.1468 (15) and 0.5405 (17) Å. The mean planes of these rings (through all ring atoms) have a dihedral angle of 49.03 (10)°. In the crystal, mol­ecules are linked by O—H⋯O hydrogen bonds. The absolute configuration of the mol­ecule was established, as judged by the, as judged by the obtained values for the Hooft and Flack parameters.