N-(9,11-Dimethoxy-4-oxo-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinolin-3-yl)benzamide

The title schulzeine derivative, C22H24N2O4, crystallizes with two crystallographically independent molecules of almost identical conformation in the asymmetric unit. The tricyclic core of schulzeine has a fused-three-ring system comprising the tetrahydroisoquinoline and δ-lactam moieties. In both molecules, the pyridine ring adopts a twisted-boat conformation, whereas the lactam ring is in a boat conformation. The two methoxy groups are slightly twisted from the attached benzene ring [C—O—C—C torsion angles = −21.3 (2) and −20.5 (2)° in molecule A, and −6.3 (2) and −16.2 (2)° in molecule B] and the benzamide moiety is in a (−)-synclinal conformation with respect to the lactam ring. In the crystal, molecules are linked into V-shaped dimers by intermolecular N—H⋯O hydrogen bonds and weak C—H⋯O interactions. These dimers are stacked into V-shaped columns along the a axis. Adjacent columns are further linked in an antiparallel manner. C—H⋯π interactions are also observed.

The title compound crystallized with two crystallographically independent molecues A and B in the asymmetric unit ( Fig. 1). These two molecules are almost conformationally identical with slightly different bond lengths and angles. The bond lengths in (I) are within normal ranges (Allen et al., 1987). The tricyclic core of schulzeine (C1-C13/N1/O1) has a fused-three-ring system comprising of the tetrahydro isoquinoline and δ-lactam moieties. In both molecules, the pyridine ring (C5-C9/N1) adopts a twisted boat conformation with puckering parameters Q = 0.6943 (17) Fig. 1 show that H atoms at C12 and C9 are in cis-relationship. An intramolecular C10A-H10B···O3A weak interaction (Table 1; Fig. 1) generates a S(6) ring motif (Bernstein et al., 1995).
In the crystal packing (Fig. 2), molecules are linked into V-shaped dimers by N-H···O hydrogen bonds and C-H···O weak interactions (Table 1) which generate two S(7) ring motifs (Bernstein et al., 1995). These dimers are stacked into V-shaped columns along the a axis. Adjacent columns are further linked by C-H···O weak interactions in an antiparallel manner. C-H···π interactions were also observed (Table 1); Cg 1 and Cg 2 are the centroid of C1A-C6A and C15A-C20A benzene rings, respectively.

Experimental
The title schulzeine benzamide derivative was synthesized according to the previous reported method ( Kuntiyong et al., 2006). Colourless block-shaped single crystals of the title compound suitable for x-ray structure determination were crystallized from hexane:ethylacetate (2:1 v/v) by slow evaporation at room temperature after a few days.

sup-2 Refinement
All H atoms were placed in calculated positions with d(N-H) = 0.86 Å, d(C-H) = 0.93 Å for aromatic, 0.97 for CH 2 and 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 2.33 Å from H21G and the deepest hole is located at 1.38 Å from C5B. A total of 5097 Friedel pairs were merged before final refinement as there is no large anomalous dispersion for the determination of the absolute configuration. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atomic numbering. The intramolecular C-H···O weak interaction is shown as dash line. N- (9,3,4,6,7,

Special details
Experimental. The low-temparture data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. 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.