(1S,2E,6R,7aR)-2-Benzylidene-1,6-dihydroxy-2,3,5,6,7,7a-hexahydro-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.

In the title compound, C 14 H 15 NO 3 , the conformation of the double bond was determined to be E, confirming the result obtained from two-dimensional NMR data. The fivemembered 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-HÁ Á ÁO 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.

D-HÁ
Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: publCIF (Westrip, 2010). The title compound (Fig. 1) is a new asymmetric benzyl-pyrrolizidinone which has been synthesized from a chiral Morita-Baylis-Hillman adduct. It belongs to a class of compounds with potential pharmacological properties as mediators of the LFA-1 (lymphocyte function-associated antigen 1) function, particularly as anti-inflammatory agents and for the treatment of autoimmune diseases (Baumann, 2007). It has three defined stereocenters and a double bond with E configuration. The five membered rings N1/C3/C2/C1/C7A and N1/C5/C6/C7/C7A of the pyrrolizine moiety exhibit C2and C5-envelope conformations, respectively, with C2 and C5 atoms displaced from the mean-planes formed by the remaining rings atoms by 0.1468 (15) and 0.5405 (17) Å, respectively. The mean planes of these rings have a dihedral angle of 49.03 (10)°. The configuration of the double bond determined by X-ray crystallography confirms the twodimensional-NOESY NMR analysis. The crystal structure is stabilized by intermolecular hydrogen bonds (Tab. 1 and Fig.   2).

Experimental
The title compound was prepared using a synthetic sequence previously described (Freire et al., 2011) and purified by flash silica gel column chromatography (CH 2 Cl 2 :MeOH -solvent gradient: 100:0 to 95:05) to afford 0.14 g (as a white solid) in 76% yield, followed by recrystallization using the liquid-vapor saturation method. Subsequently, it was dissolved in ethanol and crystallized under the vapor pressure of ethyl ether (a less polar liquid), in a closed camera, thus allowing for the slow formation of good diffracting crystals.

Refinement
The calculated Flack parameter was F = 0.1 (3) (Flack, 1983). Further analysis OF the absolute structure was performed with PLATON (Spek, 2009), using likelihood methods (Hooft et al., 2008). The calculated value for the Hooft parameter was y = 0.01 (2), with a corresponding probability of 1x10 -100 for an inverted structure. These results unequivocally indicate that the absolute structure has been correctly assigned. All H atoms were placed in calculated positions with O-H = 0.84 Å and C-H = 0.95, 0.99 and 1.00 Å for aryl, methylene and methyne H-atoms, respectively, and refined in the riding model approximation with U iso (H) = 1.5 U eq (O) or 1.2 U eq (C).

Computing details
Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT (Bruker, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: publCIF (Westrip, 2010).  The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius. 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 R-factors(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.