4-Cyano-N-ethylspiro[chromene-2,4′-piperidine]-1′-carboxamide

The title compound, C17H19N3O2, crystallizes with two independent molecules (A and B) in the asymmetric unit. In both molecules, the pyran ring has a twisted conformation (5 S 4), with Q = 0.301 (3) Å, θ = 116.7 (6) and ϕ= 213.6 (7)° for molecule A, and Q = 0.364 (2) Å, θ = 113.7 (3) and ϕ = 213.0 (4)° for molecule B. In molecule B, the terminal ethyl group is disordered over two orientations with an occupancy ratio of 0.55 (1):0.45 (1). In the crystal, molecules A and B form very similar but separate R 1 2(7) motifs through N—H⋯O and C—H⋯O hydrogen bonds. The resulting chains along [001] are interlinked by weaker C—H⋯O and C—H⋯π interactions, forming layers parallel to the bc plane.

The title compound contains two molecules in the asymmetric unit (Fig. 1). The piperidine ring forms dihedral angles of 11.9 (2)° and 78.2 (1)° for molecule A, 7.9 (8)° and 74.3 (1)° for molecule B, with the N-ethyl carboxamide group and chroman ring, respectively. The pyran ring in the molecules A and B (C8/C7/C2/O1/C1/C9) adopts a twisted conformation ( 5 S 4 ) with O1 and C1 atoms deviating respectively from the mean plane defined by the rest of the atoms by Molecules A and B form separate chains along [001] through similar R 2 1 (7) motifs (Bernstein et al., 1995) through N-H···O and C-H···O hydrogen bonds. The chains made of molecules B form layers parallel to bc plane owing to formation of an additional C9B-H9B···O2B hydrogen bond. The crystal structure also has a noteworthy C-H···π interaction that appears to be a weaker link between molecules A and B resulting in layers parallel to the (100) plane ( Fig.2 and Fig.3).

Experimental
Trimethylsilylcyanide (1.2 mmol) was added to a mixture of N-ethyl-4-oxospiro[chroman-2,4′-piperidine]-1′carboxamide (1.0 mmol) and catalytic amount of ZnI 2 in dichloromethane (10 vol) under a nitrogen atmosphere. The reaction mixture was stirred at 50°C for 6 h and then cooled down to the room temperature; then diluted HCl (5 ml) was added and stirring continued for additional 2 h. The solution was extracted with ethylacetate (20 ml), dried over Na 2 SO 4 and evaporated to dryness. The crude product was dissolved in benzene (10 ml), to which tosic acid (0.1 mmol) had been added, and the solution was heated to reflux for 2 h. After completion of the reaction as indicated by TLC, the reaction mixture was concentrated under reduced pressure. The residue was diluted with ethylacetate (20 ml), washed with bicarbonate solution (10 ml) dried and concentrated. The crude product was purified by column chromatography to provide the desired product as colorless solid. Crystals of the title compound were grown from its solution in ethanol by slow evaporation at room temperature.

Refinement
The positions of the hydrogen atoms bound to N3A, C11A, C13A, N3B, C9B and C11B were allowed to refine with isotropic temperature factors since they participate in the hydrogen-bonding. All other hydrogen atoms were included into the model at geometrically calculated positions (C-H target distance 0.96 Å for methyl hydrogen atoms, 0.93 Å for all others) and refined using a riding model with their U iso constrained to 1.2 times U eq (1.5 times for methyl H atoms) of the respective atom to which the hydrogen atom binds. The methyl H atoms involving the C16 atom of molecules A and B were allowed to refine with their torsion angles optimized. In molecule B, the terminal ethyl group C15B and C16B is disordered over two sets of sites the treatment of which converged with occupancy values of 0.55 (1) and 0.45 (1) for the major and minor components, respectively.

Figure 1
The molecules of the title compound with atom-labeling scheme. Displacement ellipsoids are drawn at 30% probability.
For the sake of clarity, H atoms are not shown.   The layers formed by molecules B along (100) plane. Non-essential groups and most hydrogen atoms were omitted for clarity. 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.