6-Butyl-5-(4-methoxyphenoxy)-3-phenyl-3H-1,2,3-triazolo[4,5-d]pyrimidin-7(6H)-one

The asymmetric unit of the title compound, C21H21N5O3, consists of two geometrically similar molecules. The fused rings of the triazolo[4,5-d]pyrimidine system are nearly coplanar, making dihedral angels of 1.48 (18) and 1.34 (16)°, and the phenyl rings are twisted by 12.3 (1) and 8.7 (1)° with respect to the triazolopyrimidine plane. The ethyl groups of the n-butyl side chains are disordered over two sites in each of the independent molecules, the ratios of occupancies being 0.60:0.40 and 0.61:0.39.

In recent years, Zhao's group succeeded in synthesizing the derivatives of 8-azaguanine via aza-Wittig reaction of betaethoxycarbonyl iminophosphorane with aromatic isocyanates (Zhao, Xie et al., 2005). As a continuation of the quest for new biologically active derivatives of 8-azaguanine, the title compound was obtained from beta-ethoxycarbonyl iminophosphorane and aliphatic isocyanate and structurally characterized.
The asymmetric unit of the crystal of the title compound, C 21 H 21 N 5 O 3 , consists of two geometrically similar molecules ( Fig. 1), the bond lengths and angles in triazolopyrimidinone moiety are in good agreement with those observed for a closely related structures (Zhao, Hu et al., 2005;Zhao, Wang & Ding, 2005). The fused rings of the triazolo[4,5d]pyrimidine ring system are as usual coplanar (e.g. see structures by Wang et al., 2006 andZeng et al., 2009), and the phenyl rings are twisted with respect to the triazolopyrimidine plane by 12.3 (1)° and 8.7 (1)° in each of the two independent molecules.

S2. Experimental
To the solution of carbodiimide, prepared according to Zeng et al. (2006)

S3. Refinement
All H atoms were placed in the geometrically calculated positions and treated as riding atoms, with C-H = 0.93-0.97 Å, and U iso (H) = 1.2U eq (C) [1.5U eq (C) for methyl H atoms]. The terminal ethyl groups of the n-butyl substituent are disordered in both molecules; the occupancy refinement yielded ratio 0.60 : 0.40 and 0.61 : 0.39 for each of the two molecules. The bond lengths and the 1,3-distances in these groups were restrained during the refinement to be within the ranges of 1,54 ± 0.01 Å and 2.45 ± 0.01 Å respectively.

Figure 1
The asymmetric unit of the title compound with atomic numbering scheme and displacement ellipsoids drawn at the 30% probability level; only major components of disordered butyl groups are shown. H-Atoms are omitted.

6-Butyl-5-(4-methoxyphenoxy)-3-phenyl-
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.