Crystal structure of ethyl 2-amino-4-(4-chlorophenyl)-4H-1-benzothieno[3,2-b]pyran-3-carboxylate

The title compound, C20H16ClNO3S, is built up from three fused rings, one five- and two six-membered rings, linked to a 3-ethoxycarbonyl group and to a 4-chlorophenyl ring. The hydropyran ring has a flattened envelope conformation, with the C atom substituted by the 4-chlorophenyl ring as the flap (displaced by 0.077 (2) Å from the plane through the other atoms). The fused three-ring system is quasi-planar (r.m.s. deviation = 0.057 Å), with the largest deviation from the mean plane being 0.106 (1) Å for the C atom substituted by the 4-chlorophenyl ring. The 4-chlorophenyl ring is approximately perpendicular to the mean plane of the fused ring system, as indicated by the dihedral angle of 77.32 (6)° between their mean planes. There is an intramolecular N—H⋯O hydrogen bond forming an S(6) ring motif. In the crystal, molecules are linked by pairs of N—H⋯O hydrogen bonds, forming inversion dimers with an R 2 2(12) ring motif. There are also short intermolecular Cl⋯O interactions present [3.1226 (12) Å] between neighbouring molecules.

The reaction was carried out in hot alcohol in the presence of piperidine as a basic catalyst (Daisley et al., 1982). Initially the condensation gave the Michael adducts which undergoes intramolecular cyclization to afford an imino-pyran. The subsequent tautomeric transformation gives rise to the title compound, whose crystal structure we report on herein.
The molecule of the title compound, Fig. 1, is formed by three fused rings linked to an ethyl-3-carboxylate group and to a 4-chlorophenyl. The three fused rings (S1/C1-C11/O1) are nearly coplanar, with the maximum deviation from the mean plane being -0.106 (1) Å for atom C9. Its mean plane make a dihedral angle of 77.32 (6)° with the attached 4chlorophenyl ring. The pyran ring has a flat envelope conformation with atom C9, substituted by the 4-chlorophenyl ring, as the flap. There is an intramolecular N-H···O hydrogen bond, involving the amine and carboxyl ate group, forming an S(6) ring motif ( Fig. 1 and Table 1).

S2. Synthesis and crystallization
In a 100 ml flask equipped with a condenser was dissolved 4 mmol of (Z)-2-(4-chlorobenzylidene)-1-benzo[b]thiophen-3(2H)-one and 5 mmol of ethyl cyanoacetate in 30 ml of ethanol. Then, 1 ml of piperidine was added, and the reaction mixture was refluxed for 6 h. Thin layer chromatography revealed the formation of a single product. The organic phase was evaporated under reduce pressure. The resulting residue was recrystallized from ethanol (yield: 67%; m.p.: 405 K). Colourless block-like crystals of the title compound were obtained by slow evaporation of a solution in ethanol.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2  A view of the molecule structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular N-H···O hydrogen bond is shown as a dashed line (see Table 1).

Figure 2
A view along the a axis of the crystal packing for the title compound. The hydrogen bonds are shown as dashed lines (see Table 1), and C-bound H atoms have been omitted for clarity.