Tert-butyl 3-oxo-2,3,4,5,6,7-hexahydro-1H-pyrazolo[4,3-c]pyridine-5-carboxylate

In the title compound, C11H17N3O3, the pyrazole ring is approximately planar, with a maximum deviation of 0.005 (2) Å, and forms a dihedral angle of 5.69 (13)° with the plane through the six atoms of the piperidine ring. In the crystal, pairs of intermolecular N—H⋯O hydrogen bonds form dimers with neighbouring molecules, generating R 2 2(8) ring motifs. These dimers are further linked into two-dimensional arrays parallel to the bc plane by intermolecular N—H⋯O and C—H⋯O hydrogen bonds.

In the title compound, C 11 H 17 N 3 O 3 , the pyrazole ring is approximately planar, with a maximum deviation of 0.005 (2) Å , and forms a dihedral angle of 5.69 (13) with the plane through the six atoms of the piperidine ring. In the crystal, pairs of intermolecular N-HÁ Á ÁO hydrogen bonds form dimers with neighbouring molecules, generating R 2 2 (8) ring motifs. These dimers are further linked into twodimensional arrays parallel to the bc plane by intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds.
The bond lengths (Allen et al., 1987) and angles are within normal ranges and comparable to a closely related structure (Shahani et al., 2009).

Experimental
LiHMDS (1.0 M solution in toluene, 11 mmol) was added quickly to a solution of tert-butyl 4-oxopiperidine-1-carboxylate (10 mmol 15 ml of toluene) using syringe at 273 K with stirring for 10 minutes. Ethyl chloro formate (11 mmol) was then added quickly. The reaction mixture was slowly (10 minutes) brought to room temperature and stirred for 10 minutes. Acetic acid (2 ml), ethanol (15 ml), and hydrazine hydrate (30 mmol) were added and refluxed for 15 minutes. The reaction mixture was concentrated to dryness under reduced pressure and re-dissolved in ethyl acetate. The organic layer was washed with saturated brine solution, dried over Na 2 SO 4 , evaporated under reduced pressure and purified by crystallizing using ethanol (white solid). The recrystallization was done using 1:1 mixture of ethanol and acetone. Yield: 78%. M.p. 498.5-500.5 K.

Refinement
All hydrogen atoms were located in a difference map and were refined freely

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. 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.