(5S)-4-(2,2-Dimethylpropyl)-5-isopropyl-1,3,4-oxadiazinan-2-one

The title compound, C11H22N2O2, has one chiral center and packs in the monoclinic space group P21. The asymmetric unit has five crystallographically independent molecules, four of which engage in intermolecular N—H⋯O hydrogen bonding.

The title compound, C 11 H 22 N 2 O 2 , has one chiral center and packs in the monoclinic space group P2 1 . The asymmetric unit has five crystallographically independent molecules, four of which engage in intermolecular N-HÁ Á ÁO hydrogen bonding. H atoms treated by a mixture of independent and constrained refinement Á max = 0.27 e Å À3 Á min = À0.17 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1; y À 1 1968). We are interested in studying the underlying factors for differing conformations of this heterocycle and for its use as a chiral auxiliary in aldol addition reactions (Casper et al., 2002;Burgeson et al., 2004).

Related literature
The oxadiazinanone ring is well suited to accommodate H-bonded dimers of the R 2 2 (8) type (Bernstein et al., 1995;Etter et al., 1990). The H-bond occurs most naturally between the carbonyl oxygen on the first molecule and the nitrogen containing the hydrogen atom on the second molecule, and vice versa. The result is an eight-membered ring in which two of the connections are H-bonds. These H-bonded dimers have a strong propensity to form in the oxadiazinanone system (Anderson et al., 2006). A few examples of this type of H-bonding are seen in structures by Addison et al. (2008), Rodrigues et al. (2006), and Szczepura et al. (2004 (with REFCODES LOBVII, GEGZUO, and YAGJEW, respectively).
The title compound packs into a monoclinic, P2 1 , space group. This compound is unusual in that there are five molecules in the asymmetric unit (see Figure 1). The best of these is illustrated in Figure 2. Of these five molecules, two pairs are engaged in R 2 2 (8) type H-bonding. The fifth molecule does not engage in H-bonding because the donor atom is surrounded by neopentyl substituents, effectively blocking any H-bonds to an acceptor atom. Figure 3 shows all five molecules in a wireframe style, with key atoms shown in a space-fill style, to highlight how the N-H is hemmed in by neopentyl substituents. Another, interactive, view in Figure 4 shows how inaccessible the donor N really is.
The number of crystallographically independent molecules in the asymmetric unit also warrants notice. Most of the structures in the Cambridge Structural Database have a Z' less than or equal to 1. According to the August 2010 edition of the CSD (Allen, 2002), 91.1% of the structures have a Z' less than or equal to 1. As Z' increases, the percentage of structures decreases (Z'=2, 7.7%; Z'=3, 0.42%; Z'=4, 0.40%). Only 0.014% (N=73) of structures in the CSD have a Z'=5, which is a property of this structure.
Upon conducting a Mogul geometry check (Bruno et al., 2004), the N4-C10 (1.490 (5) Å) and N24-C30 bonds (1.488 (5) Å) were flagged as being outside the typical range for a C-N bond (mean 1.46 ±0.01 Å). This bond is the one between the N atom of the heterocycle and the neopentyl substituent. This bond in the other three crystallographically supplementary materials sup-2 independent molecules is not flagged. The bonds C50-C51 (1.508 (7) Å) and C90-C91 (1.507 (6) Å) were also flagged as unusual compared to the mean of 1.54 ±0.01 Å. One last bond, N84-C85, was considered unusual with a value of 1.463 (5) Å versus a mean of 1.49 ±0.01 Å. There is no obvious particular chemical or crystallographic explanation for these deviations. However, they still appear to be within an acceptable range. All angles were reported to be within normal limits.

Experimental
The title compound was prepared as previously reported (Casper et al. 2004). Single crystals were grown by vapor diffusion of hexane into an ethyl acetate solution of the title compound.

Refinement
All non-H atoms were refined anisotropically. All H atoms were initially identified through difference Fourier syntheses then removed and included in the refinement in the riding-model approximation (C-H = 0.98, 0.99 and 1.00 Å for CH 3 , CH 2 , and CH; U iso (H) = 1.2U eq (C) except for methyl groups, where U iso (H) = 1.5U eq (C)). Fig. 1. ORTEP view of the title compound showing the atomic numbering scheme of all five independent molecules in the asymmetric unit. Ellipsoids are shown at 50% probability displacement and hydrogen atoms are omitted for clarity.    Least-squares matrix: full H atoms treated by a mixture of independent and constrained refinement