(8aRS)-8,8a-Dihydrofuro[3,2-f]indolizine-6,9(4H,7H)-dione

The title compound, C10H9NO3, is a chiral molecule with one stereogenic carbon atom, but which crystallizes as a racemate in the centrosymmetric space group P21/n. The central six-membered ring of the indolizine moiety adopts a definite envelope conformation, while the conformation of the oxopyrrolidine ring is close to that of a flat-envelope with a maximum deviation of 0.352 (1) Å for the flap atom.

The title compound, C 10 H 9 NO 3 , is a chiral molecule with one stereogenic carbon atom, but which crystallizes as a racemate in the centrosymmetric space group P2 1 /n. The central sixmembered ring of the indolizine moiety adopts a definite envelope conformation, while the conformation of the oxopyrrolidine ring is close to that of a flat-envelope with a maximum deviation of 0.352 (1) Å for the flap atom.
Based on these facts and in continuation of our interest in developing simple and efficient route for the synthesis of novel indolizine derivatives, we report here the synthesis, molecular and crystal structure of the title compound, (I). The molecular structure and the atom labeling scheme are shown in Fig. 1.
The molecule crystallizes in the monoclinic space group P21/n. Accordingly, the compound is a racemate and consists of two enantiomeric pairs in the unit cell with relative configuration R and S on the C5 carbon atom. The central N-heterocyclic ring is not planar and adopts an envelope conformation for both enantiomers. A calculation of least-squares planes shows that this ring is puckered in such a manner that the five atoms C5, C6, C7, C10 and C11 are coplanar, while atom N1 is displaced from this plane with an out-of-plane displacement of 0.479 (2) Å.
The oxopyrrolidine ring attached to the indolizine ring system has a flat-envelope conformation, with atom C4 on the flap. The maximum deviation from planarity for C4 is 0.352 (1) Å. Obviously, the change of stereochemical centre on C5 from R to S causes changes in orientation of N1, C2, O1, C3 and C4.
The N1-C5 and N1-C11 bonds are approximately equivalent and both are much longer than the N1-C2 bond.
Moreover, the N1 atom is sp 2 hybridized, as evidenced by the sum of the valence angles around it [358.8 (3)° ]. These data are consistent with conjugation of the lone-pair electrons on N1 with the adjacent carbonyl and agree with literature values for simple amides (Pedersen, 1967).

Refinement
All 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 -0.98Å and O-H distance 0.85Å and U iso set at 1.2U eq of the parent atom.
supplementary materials sup-2 Figures   Fig. 1. Molecular structure of (I) with the atomic numbering scheme; the chiral centre is C5. Displacement ellipsoids are drawn at the 50% probability level (Brandenburg, 2001). 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.