2-(1,3-Benzoxazol-2-yl)-1-phenylethenyl benzoate

In the title molecule, C22H15NO3, the configuration about the ethylenic double bond is Z configuration and it is approximately coplanar with the adjacent phenyl ring and benzoxazole ring system as indicated by the C(H)=C(O)—Cphenyl—Cphenyl and Obenzoxazole—C—C(H)=C(O) torsion angles of 179.88 (15) and 5.7 (2)°, respectively. The dihedral angle between the essentially planar (r.m.s. deviation = 0.080 Å) 2-(1,3-benzoxazol-2-yl)-1-phenylethenyl group and the benzoate phenyl ring is 61.51 (6)°. A short intramolecular O⋯O non-bonded interaction of 2.651 (2) Å is present.


Comment
The reaction of 2-methylbenzoxazole (A) (Fig. 1) with acyl chlorides such as benzoyl chloride was carried out for the first time by Ciurdaru and Ciuciu (1979), who used the same conditions for reactions of other 2-methylbenzoazoles with acyl chlorides. After infra red and mass spectral investigations and elemental analysis of acylated derivatives, it was suggested that the double acylated structure of (C) was the product of these reactions. This structure differs with the double acylated structure of (D) for the product of acylation of some azoles such as 2-methylthiazoles (Zhou & Pittman, 2004), although these reactions have been done under the same conditions. In fact, based on the presented data, not only the enolester (C) but also the conjugated ketone (D) can be considered as product of the reactions of 2-methylbenzoazoles with acyl chlorides.
In addition to the molecular structure, the configuration of the ethylenic double bond in both probable structures was also questionable. In order to clarify these ambiguous situations, the crystal structure determination of the title compound was carried out.
The C8-C9 bond length (1.335 (2) Å) in the structure is within the normal range of an unconjugated ethylenic double bond. Also, due to the more resonance interaction of nonbonding electrons on the O2 with the π system of C=O relative to C=C, the O2-C16 bond length (1.3641 (17) Å) is shorter than O2-C9 (1.4010 (16) Å). These values may indicate that the π system of ethylenic double bond is not fully delocalized.
An intramolecular O1···O2 non-bonded distance (2.651 (2) Å) is shorter than the sum of the corresponding van der Waals radii (3.04 Å) (Bondi, 1964). This phenomenon is similar to the intramolecular non-bonded interactions between an oxygen atom and atoms of group VIA in the periodic table (S, Se and Te) (Markham et al., 1999) and shows that an attractive non-bonded interaction between O1 and O2 must be present in the molecule (Punte et al., 1990). This attraction may be responsible for the Z configuration becoming the preferred configuration for the ethylenic double bond (Loghmani et al., 2007).

Experimental
The title compound was prepared as in the literature (Ciurdaru & Ciuciu, 1979), except that benzoyl chloride and triethylamine (both 30 mmol) were used to complete the reaction. Suitable single crystals for X-ray analysis were obtained from an ethanol solution of the title compound at room temperature.
supplementary materials sup-2 Refinement All H-atoms were positioned geometrically and refined using a riding model with C-H distances = 0.95 Å (both aryl and vinyl-H) and isotropic displacement parameters for these atoms were U iso (H) = 1.2U eq (C). Fig. 1. Reactions of 2-methylbenzoazoles with acyl chlorides (benzoyl chloride) in the presence Et 3 N under reflux conditions and probable products.