5-[(E)-Methoxy(phenyl)methylidene]-1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazole

In the title compound, C28H23N3O, the 1,2,4-triazole ring deviates slightly from planarity adopting a N3 T C2 conformation which is distorted towards an E C2 conformation. The plane around the ethylene unit makes a dihedral angle of 17.32 (11)° with the mean plane [r.m.s. deviation = 0.036 (1) Å] of the 1,2,4-triazole fragment. The dihedral angles between the four phenyl rings and the 1,2,4-triazole ring are 31.01 (10), 49.01 (8), 78.55 (6) and 41.51 (9)°. In the crystal, molecules are linked along [100] by weak C—H⋯O hydrogen bonds.

To understand the structure of these intermediates, we report herein the crystal structure of the title compound.
In the title molecule ( Fig. 1), the 1,2,4-triazole fragment is nearly planar, with a mean deviation of 0.036 (1) Å from the least-squares plane defined by the five constituent atoms.
The asymmetric unit contains one molecule of the title compound which is shown in Figure 1.
Puckering analysis [Cremer et al. (1975)] reveals that the 4,5-dihydro-1H-1,2,4-triazole ring adopts a N3 T C2 conformation which is distorted towards a E C2 conformation. In a related structure [Nair et al. (2008)] of a compound which is different from the title compound only through the substituent connected by a double bond with the 4,5-dihydro-1H-1,2,4-triazole ring, the latter ring is planar and not puckered. The methoxy(phenyl)methylene group is bound to the 4,5-dihydro-1H-1,2,4-triazole ring in a distance of 1.358 (3) Å which indicates a double bond. However, the plane of the heterocycle and the plane around the methylene atom are not coplanar but enclose a dihedral angle of 17.32 (11)°. In the related structure, the corresponding dihedral angle is 42.5 (4)°. The plane of the phenyl ring bound to the methylene atom is not coplanar with the plane around the methylene atom as well (dihedral angle 34.14 (10)°). The dihedral angles between the four phenyl rings and the mean plane of the 1,2,4-triazole ring are 31.01 (10)° [the C3-C8 phenyl ring], 49.01 (8)° [the C9-C14 phenyl ring], 78.55 (6)° [the C15-C20 phenyl ring] and 41.51 (9)° [the C22-C27 phenyl ring]. In the crystal packing, molecules are connected by weak C-H···O hydrogen bonds (Table 1).

Experimental
To an oven dried Schlenk-flask charged with NaH (48 mg, 2.0 mmol), tBuOK (11 mg, 98 mol), and 5-(methoxy(phenyl)methyl)-1,3,4-triphenyl-4H-1,2,4-triazolium chloride (454 mg, 1.00 mmol) was added dry THF (15 ml) under nitrogen and the reaction mixture was allowed to stir for 4 h in the dark. The solvent was then removed under vacuum, and the residue was suspended in dry toluene (20 ml) and filtered through a celite pad under nitrogen. Then the solvent was evaporated to give 296 mg (0.709 mmol, 71%) of the title compound as 10:1 mixture of E:Z isomers. Crystals suitable for X-ray crystallography were grown by cooling down a saturated acetonitrile solution at -30 °C under argon for 48 h.

Refinement
C-bound H atoms were positioned geometrically (C-H = 0.98 Å for aliphatic, 0.95 Å for aromatic H) and treated as riding on their parent atoms [U iso (H) = 1.2U eq (C, aromatic), U iso (H) = 1.5U eq (C, aliphatic)]. The methyl group was allowed to rotate along the C-O bond to best fit the experimental electron density.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.

5-[(E)-Methoxy(phenyl)methylidene]-1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazole
Crystal data 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 > 2σ(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.