(6S,7S,8R,8aS)-6-Ethylperhydroindolizine-7,8-diol

In the title compound, C10H19NO2, the piperidine and pyrrolidine rings of the perhydroindolizine ring system adopt chair and envelope conformations, respectively. In the crystal structure, intermolecular O—H⋯N and O—H⋯O hydrogen bonds link the molecules into a chain running along the a axis.

In the title compound, C 10 H 19 NO 2 , the piperidine and pyrrolidine rings of the perhydroindolizine ring system adopt chair and envelope conformations, respectively. In the crystal structure, intermolecular O-HÁ Á ÁN and O-HÁ Á ÁO hydrogen bonds link the molecules into a chain running along the a axis.
Based on these facts and in continuation of our interest in developing simple and efficient route for the synthesis of novel monohydroxylated indolizine derivatives, we report here the synthesis, molecular and crystal structure of the title compound, (I). The absolute configuration was established by synthesis and is depicted in the scheme and figure. The expected stereochemistry of atoms C5, C6, C7 and C8 was confirmed as S, R, S and S, respectively (Fig. 1). The central six-membered ring is not planar and adopts a chair conformation (Cremer & Pople, 1975). A calculation of least-squares planes shows that this ring is puckered in such a manner that the four atoms C6, C7, C9 and N1 are coplanar to within 0.019 (2) Å, while atoms C5 and C8 are displaced from this plane on opposite sides, with out-of-plane displacements of -0.720 (2) and 0.636 (1) Å, respectively. In the molecule, the pyrrolidine ring N1/C2-C5 exhibits an envelope conformation with envelope on atom N1 (Nardelli, 1983). The displacement of atom N1 from the mean plane of the remaining four atoms is 0.625 (2) Å. The N1-C2, N1-C5 and N1-C9 bonds are approximately equivalent. Atom N1 is sp 3 -hybridized, as evidenced by the sum of the valence angles around it [327.05 (2)°]. Intermolecular O-H···N and O-H···O hydrogen bonds link the neighbouring molecules of (I) into extended chains, which run parallel to the a axis ( Fig. 2) and help to stabilize the crystal structure of the compound. Atom N1 (O1) participates as acceptor and atom O1 (O12) as donator in these intermolecular hydrogen bonds.

Refinement
Hydroxyl H atoms were located in a difference Fourier map and their positions were refined freely, with U iso (H) = 1.2U eq (O).
Other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances in the range 0.93-0.98 Å, and with U iso (H) = 1.2U eq (C). The absolute configuration could not be reliably determ-supplementary materials sup-2 ined for this compound using Mo radiation, and has been assigned according to the synthesis. 1061 total Friedel pairs have been merged. Fig. 1. Molecular structure of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.  Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Figures
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.