2-Phenyl-2-(pyridin-2-yl)hexahydropyrimidine

The title compound, C15H17N3, was prepared by reaction of benzoylpyridine and hexahydropyrimidine. The 1,3-diazinane ring adopts a chair conformation with one N—H group axial and the other equatorial. The axial N—H group participates in very weak hydrogen bonding to the lone pair of electrons of the N atom with the equatorial H atom producing a very weakly hydrogen-bonded dimer. The pyridine N atom accepts an internal hydrogen bond from the equatorial H atom. The phenyl ring adopts an equatorial position while the pyridine ring is axial. The phenyl ring exhibits a slight twist (ca 25°) relative to the hexahydropyrimidine ring. The pyridine ring stacks with symmetry-related pyridine rings.

The title compound, C 15 H 17 N 3 , was prepared by reaction of benzoylpyridine and hexahydropyrimidine. The 1,3-diazinane ring adopts a chair conformation with one N-H group axial and the other equatorial. The axial N-H group participates in very weak hydrogen bonding to the lone pair of electrons of the N atom with the equatorial H atom producing a very weakly hydrogen-bonded dimer. The pyridine N atom accepts an internal hydrogen bond from the equatorial H atom. The phenyl ring adopts an equatorial position while the pyridine ring is axial. The phenyl ring exhibits a slight twist (ca 25 ) relative to the hexahydropyrimidine ring. The pyridine ring stacks with symmetry-related pyridine rings.

Related literature
For recent reports of the structures of other hexahydropyrimidines, see: Al-Resayes (2009);Song et al. (2010) and references therein. For general structural parameters for organic molecules, see: Allen et al. (1987). For the extinction correction, see: Zachariasen (1968 Table 1 Hydrogen-bond geometry (Å , ).  The 1,3-diazinane ring adopts a chair conformation with the pyridine ring in the axial position. The pyridine nitrogen (N1) accepts an internal hydrogen bond from N3, a situation similar to that found in 2-methyl-2-(2-pyridyl)1,3-diazinane (Al-Resayes, 2009). N3 has its hydrogen atom (H16) in an equatorial position. The other amine nitrogen (N2) has its hydrogen atom (H17) in an axial position. H17 forms what appears to be a very long, very weak hydrogen bond to N3 in an adjacent molecule (1 -x, -y, 1 -z) (N2···N3 4.118 Å). H17 of that adjacent molecule hydrogen bonds to N3 of the original molecule, producing a very weakly hydrogen bonded dimeric pair. This is shown in Figure 2.
A more significant packing interaction is aromatic ring stacking of adjacent pyridine rings. This is shown in Figure 3 with the adjacent molecule at (-x, -y, 2 -z).
The phenyl ring is twisted out of the plane defined by N2, N3, C13 and C15 of the 1,3-diazinane ring by 25.1 °. This twist removes the potential steric strain between H9 of the phenyl ring and the equatorial internally hydrogen bonded H16.
The distances within the title compound are very similar to those found in 2-methyl-2-(2-pyridyl)1,3-diazinane (Al-Resayes, 2009). Interestingly, in both compounds, the C4-C5 distance is the longest within the pyridyl ring, and in the title complex, the C7-C8 distance is the longest within the phenyl ring. Both of these bonds are relatively near N2, and are longer than the typical range (Allen et al., 1987).
Experimental 2-Benzoylpyridine (3.66 g, 20.0 mmol) was dissolved in 15 ml anhydrous ethanol. 1,3-Diaminopropane (0.835 ml, 10.0 mmol) was added and the resultant mixture was refluxed for about six and a half hours. The light brown solution was concentrated on a rotary evaporator to a light brown syrup. The syrup was allowed to stand for four weeks affording a relatively large mass of colorless crystals intermixed with a brownish semisolid material. This mixture was washed repeatedly with anhydrous ethanol at 0 ° C and decanted to remove the brownish material. The washed crystalline mass was dissolved in warm (35 ° C) anhydrous ethanol and refrigerated. After three days, colorless, cuboidal crystals were observed and proved suitable for X-ray data collection.

Refinement
The two N-H hydrogen atoms were located in difference maps. Their positions were refined giving N-H distances around 0.90 Å. All of the remaining hydrogen atoms were placed in calculated Positions (E-H of 0.95 Å) and were refined using supplementary materials sup-2 a riding model. All hydrogen atoms were assigned thermal parameters 1.2 times larger than the corresponding U eq of the covalently bonded atoms. Fig. 1. Perspective drawing of the title compound with displacement ellipsoids drawn at the 50% probability level.