tert-Butyl N-[(3R,4R)-1-(2-cyanoacetyl)-4-methylpiperidin-3-yl]-N-methylcarbamate

The piperidine ring of the title compound, C15H25N3O3, adopts a slightly distorted chair conformation with the cis substituents displaying an N—C—C—C torsion angle of 43.0 (3)°. The cyano group (plane defined by C—C—C N atoms) is bent slightly out of the plane of the amide group by 13.3 (2)°. The carbamate group is oriented at a dihedral angle of 60.3 (5)° relative to the amide group.

In the crystal structure of the title compound the piperidine ring adopts a slightly distorted chair conformation with a torsion angle between the cis substituents of 43.0 (3)°. The carbamate group shows a dihedral angle of 60.3 (5)° relative to the amide group. The plane defined by atoms C17, C19, C20 and N21 is slightly bent out of the plane of the amide group by 13.3 (2)°.

Experimental
The title compound was prepared by cyanoacetylation of a precursor possessing a free piperidine NH-function (Babu et al., (2010)) using dicyclohexylcarbodiimide (DCC) and cyanoacetic acid. carbamate (2.80 g, 12.3 mmol) was dissolved in 25 ml of dry methylen chloride and stirred under argon atmosphere. Cyano acetic acid (0.82 g, 9.64 mmol) and N,N′-dicyclohexylcarbodiimide (1.99 g, 9.64 mmol) was added in one portion while cooling with ice. After 15 min at 273 K, the ice bath was removed, the mixture warmed to room temperature (298 K) and stirring was continued for 3 h. N,N′-dicyclohexylurea was removed by filtration, washed with methylen chloride and the filtrate concentrated under reduced pressure.

tert
Purification by column chromatography (SiO 2 , methylen chloride/ethyl acetate: 7 + 3) yielded the title compound as colorless solid (2.18 g, 84.3%). Crystals of the title compound were obtained by slow evaporation of methanol at room temperature (298 K).

Refinement
Hydrogen atoms attached to carbons were placed at calculated positions with C-H = 0.95 Å (aromatic) or 0.99-1.00 Å (sp 3 C-atom). All H atoms were refined with isotropic displacement parameters (set at 1.2-1.5 times of the U eq of the parent atom). Because no strong anomalous scattering atoms are present Friedel opposites were merged in the refinement.
The absolute configuration was assigned according to the synthesis.

Figure 1
Crystal structure (oder molecular structure) of the title compound with labeling and displacement ellipsoids drawn at the 50% probability level. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.17 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.