Ethyl 5-methyl-7-phenyl-1,2,4-triazolo[4,3-a]pyrimidine-6-carboxylate

In the title compound, C15H14N4O2, the triazolopyrimidine ring system is almost planar (r.m.s. deviation = 0.02 Å) and the phenyl ring is inclined to its mean plane by 42.45 (9)°. The carboxyl group is inclined to the triazolopyrimidine ring mean plane by 57.8 (3)°. In the molecule, there is a short C—H⋯O contact involving the carbonyl O atom and an H atom of the adjacent methyl substituent. In the crystal, neighbouring molecules are linked by C—H⋯O hydrogen bonds, forming chains propagating along [010]. There are also weak π–π interactions present involving the pyridine and phenyl rings of neighbouring chains [intercentroid distance = 3.8580 (16) Å].

In the title compound, C 15 H 14 N 4 O 2 , the triazolopyrimidine ring system is almost planar (r.m.s. deviation = 0.02 Å ) and the phenyl ring is inclined to its mean plane by 42.45 (9) . The carboxyl group is inclined to the triazolopyrimidine ring mean plane by 57.8 (3) . In the molecule, there is a short C-HÁ Á ÁO contact involving the carbonyl O atom and an H atom of the adjacent methyl substituent. In the crystal, neighbouring molecules are linked by C-HÁ Á ÁO hydrogen bonds, forming chains propagating along [010]. There are also weakinteractions present involving the pyridine and phenyl rings of neighbouring chains [intercentroid distance = 3.8580 (16) Å ].   Table 1 Hydrogen-bond geometry (Å , ).  Supporting information for this paper is available from the IUCr electronic archives (Reference: SU2724).

Introduction
Annelated pyrimidine derivatives have gained considerable interest as promising vasodilating agents (Jeanneau-Nicolle et al., 1992;Ali et al., 2011). Triazolopyrimidines in particular have shown antihypertensive as well as diuretic activities (Ali et al., 2011). The title compound has a triazolopyrimidine nucleus and was derivatized from the well known Biginelli dihydropyrimidine calcium channel blockers (Rovnyak et al., 1995;Triggle & Padmanabhan, 1995;Ohno et al., 2002). It has been shown to possess potential ex vivo calcium channel blocking activity (Farghaly et al., 2013). In the present investigation, the crystal structure of the title compound was obtained in an effort to gain information pertaining to the role of regiocontrol in the cyclization step as well as electronic induction in the conformation of such a molecule.

Discussion
The stereochemistry of the title compound, Fig. 1, revealed that the product has retained its original stereochemistry, and that cyclization has occurred on N 1 as predicted from HMBC (Heteronuclear Multiple Bond Correlation experiment). A close contact between the ester moiety and the phenyl group is also evident.
In the title compound, the triazolopyrimidine ring system is planar [r.m.s. deviation 0.02 Å] and its mean plane is inclined to the phenyl ring (C10-C15) by 42.45 (9) °. The carboxyl group (COO) is inclined to the triazolopyrimidine ring mean plane by 57.8 (3) °. It occupies a cis position relative to C5═C6 double bond of the triazolopyrimidine ring system thus allowing potential stabilization of such a conformation. There is a short C-H···O contact involving atom O2 and an H atom of the adjacent methyl substituent (C9), see Table 1. The ester group is again oriented away from the phenyl ring substituent for steric considerations with a torsional angle C4-C5-C6-O1 = -56.1 (3)°.

Synthesis and crystallization
A solution of ethyl 2-hydrazino-6-methyl-4-phenylpyrimidine-5-carboxylate (0.27 g, 1 mmole) in formic acid (5 ml) was heated under reflux for 27 h. The reaction mixture was concentrated to a small volume and diluted with ice-cold water.
The precipitate was filtered, washed with water and dried. Colourless crystals of the title compound were obtained by slow evaporation of a solution in aqueous ethanol.

Refinement
The H atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 -0.98 Å with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (C) for other H atoms.

Figure 1
A view of the molecular structure of the title molecule, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The intramolecular C-H···O hydrogen bond is shown as a dashed line (see Table 1 for details).

Figure 2
A view along the a axis of the crystal packing of the title compound. The C-H···O hydrogen bonds are shown as a dashed line (see Table 1 for details).