(6,6-Dimethyl-1-phenyl-6,7-dihydro-5H-pyrrolizin-2-yl)(thiophen-2-yl)methanone

In the title compound, C20H19NOS, the pyrrolizine ring is essentially planar (r.m.s. deviation = 0.001 Å) while the fused dihydro-pyrrolizine ring adopts an envelope comformation with the C atom bearing the methyl substituents as the flap. The dihedral angles between the pyrrolizine and the phenyl and thiophene rings are 34.54 (7) and 44.93 (7)°, respectively. In the crystal, weak C—H⋯O hydrogen bonds link the molecules into infinite zigzag chains parallel to the b-axis direction.

In the title compound, C 20 H 19 NOS, the pyrrolizine ring is essentially planar (r.m.s. deviation = 0.001 Å ) while the fused dihydro-pyrrolizine ring adopts an envelope comformation with the C atom bearing the methyl substituents as the flap. The dihedral angles between the pyrrolizine and the phenyl and thiophene rings are 34.54 (7) and 44.93 (7) , respectively. In the crystal, weak C-HÁ Á ÁO hydrogen bonds link the molecules into infinite zigzag chains parallel to the b-axis direction.

Related literature
For the synthesis of the title compound, see: Dannhardt & Obergrusberger (1979). For a similar structure, see: Liu et al.  Table 1 Hydrogen-bond geometry (Å , ).
In the crystal, weak intermolecular C-H···O (Table 1) hydrogen bonds can be found, linking adjacent molecules along the b axis to form one-dimensional zigzag chains, which contributes to the stable packing of molecules in the crystal. No π-π stacking interactions were found in this crystal structure.

Experimental
A stirred solution of 5-phenyl-3,3-dimethyl-3,4-dihydro-1H-pyrrolizine in CH 2 Cl 2 was treated with a solution of 3bromo-2-thenoylethanone. The mixture was stirred for 4 h at room temperature, an aqueous solution of NaHCO 3 was added and stirred for 3 h. Then water was added to form a clear aqueous layer, the organic layer was separated and dried (anhydrous Na 2 SO 4 ) before the solvent was evaporated. The solution was evaporated under reduced pressure and purified by chromatography on a silica gel column, eluting with a petroleum ether/acetone mixture to give 32% yield of light yellow solid. The purity of the title compound was verified by elemental analysis: calculated for C 20 H 19 NOS: C 74. 73, H 5.96, N 4.36; found C 74.59, H 5.98, N 4.35. EI-MS m/z: 322(M+H) + .
The crystal appropriate for X-ray data collection was obtained from DMF-H 2 O solution at room temperature after about a week.

Refinement
All H atoms were placed in geometically idealized positions and constrained to ride on their parent atoms with C-H distances of 0.93 (0.97 for CH 2 )Å for CH, and U iso (H) = 1.2 (1.5 for CH 3 ) U eq (C).

Figure 1
View of the molecule of (I) showing displacement ellipsoids drawn at the 30% probability level. 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.