2,6-Dimethyl-4-oxo-3-oxatricyclo[5.2.1.02,6]decane-1-carboxamide

In the title compound, C12H17NO3, which was synthesized by Wagner–Meerwein rearrangement of the N-nitroimine, the ring-junction C—C bond length is comparatively long [1.573 (2) Å] due to a steric repulsion between the methyl groups at these atoms, which also leads to an increase in the C—C—C angles along this C4 chain [118.10 (13) and 115.04 (15) °, respectively]. In the crystal, N—H⋯O—C and N—H⋯O=C hydrogen bonds are formed between the amide group and the two O-atom acceptors of the lactone group, forming a chain along [001].

In the title compound, C 12 H 17 NO 3 , which was synthesized by Wagner-Meerwein rearrangement of the N-nitroimine, the ring-junction C-C bond length is comparatively long [1.573 (2) Å ] due to a steric repulsion between the methyl groups at these atoms, which also leads to an increase in the C-C-C angles along this C 4 chain [118.10 (13) and 115.04 (15) , respectively]. In the crystal, N-HÁ Á ÁO-C and N-HÁ Á ÁO C hydrogen bonds are formed between the amide group and the two O-atom acceptors of the lactone group, forming a chain along [001].
In the structure of (II) (Fig. 1), angle deviations at Csp 3 atoms range from 94.22 to 118.10 (16) °. Thus the C1-C7-C4 angle as in other previously reported compounds has a reduced value of 94.22 (12) ° (Noe et al., 1996;Knollmuller et al., 1998). Most bond distances for compound (I) were in the expected range however, the C5-C6 bond length is 1.573 (2) Å, which is apparently due to steric repulsion between the methyl groups on these atoms, this also leads to an increase in the angles C5C6C10 and C6C5C9 to 118.10 (13) and 115.04 (15) °, respectively. It is interesting to note that the bond O4-C6 is slightly longer (1.4714 (16) Å) and O4-C12 shorter (1.335 (2) Å) compared with the values previously found (average 1.45 and 1.36 Å, respectively). Intermolecular hydrogen bonds are formed through N-H···O-C and N-H···O═C between the amide and two O-atom acceptors of lactone group. (Table 1).

Experimental
The synthesis of the nitroimine (I) (Fig. 2) was carried out as follows. A solution of compound I (1.00 g, 4.16 mmol) in methanol (10 ml) was added to a mixture of acetone cyanohydrin 2 mmol (0.708 g) and potassium hydroxide 1.5 mmol (0.35 g) in distilled water. The resulting mixture was stirred and refluxed for 20 min. After cooling in ice an excess of 3 N aqueous hydrochloric acid was added over 5 min with vigorous stirring. Almost immediate precipitation of carboxamide was accompanied by gas (N 2 O) evolution. The amide was filtered off, washed with distilled water (2x10 mL), dried in a vacuum desiccator overnight and recrystallized from absolute 2-propanol. Yield: 0.86 g 93%; m.  16.55, 20.76, 24.99, 28.53, 37.35, 44.82, 48.14, 49.56, 62.19, 97.18, 177.35,178.65

Refinement
Amide H-atoms were located in a difference-Fourier synthesis and both positional and displacement parameters were allowed to refine. Other hydrogen atoms were positioned geometrically, with C-H = 0.96-0.98 Å and were allowed to ride on their parent atoms, with U iso (H) = 1.2U eq (methine or methylene C) or 1.5U eq (methyl C). In the absence of a suitable heavy atom, the absolute configuration of the title compound could not be determined (1146 Friedel pairs).

Figure 1
The molecular structure and atom nunbering scheme for the title compound, showing 30% probability displacement ellipsoids.

Figure 2
The synthetic route to the title compound (II). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.