Crystal structure of methyl 1,3-benzoxazole-2-carboxylate

The herringbone structure of methyl 1,3-benzoxazole-2-carboxylate is characterized by strong C—H⋯N and weak C—H⋯O hydrogen bonds, and further stabilized by C—O⋯π and π–π interactions.


Chemical context
Benzoxazoles are common in natural products and represent an important class of key structural motifs, often incorporated as building blocks in ligands to target a variety of receptors and enzymes in medicinal chemistry studies (Demmer & Bunch, 2015;Kamal et al., 2020). They are also a scaffold of prime importance for fluorescent probes and materials (Carayon & Fery-Forgues, 2017;Fery-Forgues & Vanucci-Bacqué, 2021). Methyl-1,3-benzoxazole-2-carboxylate (1) belongs to this family and much attention has been paid to its preparation.

Structural commentary
The title compound ( Fig. 1) crystallizes in the monoclinic space group P2 1 and exhibits the expected bond lengths and angles for a benzoxazole. The N1-C1 bond, which corresponds to a double bond, is significantly shorter [1.293 (2) Å ] than the other bonds (>1.36 Å ) of the oxazole cycle. The molecule is almost planar [N1-C1-C2-O3 = À6.7 (2) ]. The heterocyclic and carbonyl oxygen atoms O1 aand O2, respectively, are located on the same side with respect to the long axis of the molecule.

Supramolecular features
In the crystal structure, molecules are displayed according to the packing type, i.e. a flattened herringbone featuring stacks of parallel, translationally related molecules (Desiraju et al., 1989;Campbell et al., 2017)   The molecular structure of the title compound with the atom numbering. The displacement ellipsoids are drawn at the 50% probability level.  (Table 3).

Database survey
Benzoxazole-based molecules have given an umpteen number of crystal structures. A search of the Cambridge Structural Database (CSD, version of November 2020; Groom et al., 2016) found only twelve benzoxazoles substituted by a carbonyl group on the 2-position. In almost half of the cases, the benzoxazole derivative is used as a ligand to complex an Ni, Co or Cu atom (CAYSIG and CAYSOM; Iasco et al., 2012;LAJNAN;Zhang et al., 2010), or incorporated in a macromolecule (NESPUY; Lim et al., 2012;LUYJUL;Osowska & Miljanić, 2010), resulting in a geometry quite far from that of a small entity. Among the remaining examples, the benzoxazolylcarbonyl moiety may be linked to an aromatic group. When the latter is a phenyl group, the molecule is almost planar (ROFZUJ; Boominathan et al., 2014). With another benzoxazole heterocycle, the dihedral angle is only around 8 (AGESUD; Boga et al., 2018). In contrast, this angle almost reaches 71 with a benzoic acid that is involved in many intermolecular interactions (DEJGEE; Ling et al., 1999), and when the benzoxazole and phenyl derivative moieties are attached via a flexible linker (KONTEP; Deng et al., 2019). Finally, the benzoxazolylcarbonyl moiety may be linked to an aliphatic moiety, which may be rather bulky like a bornane-1,2-sultam moiety (BAKRIQ; Pią tek et al., 2011), or smaller like a morpholine moiety (JAXMED; Xing et al., 2017). In both cases, the network is structured by an interaction between the carbonyl oxygen of one molecule and the hydrogen atom borne by the C7 carbon of a neighbouring molecule. Finally, the framework closest to that of the title compound is an isopropyl 4-acetyl-5-hydroxy-1,3-benzoxazole-2-carboxylate (MIMZUG; Tangellamudi et al., 2018). In this molecule, the hydroxyl and the acetyl substituents form intramolecular hydrogen bonds while the carbonyl oxygen of one molecule interacts with the isopropyl group of the neigbouring one to form some kind of dimer. In general, planar molecules tend to assemble in layers (AGESUD; Boga et al., 2018;MIMZUG;Tangellamudi et al., 2018) and even in ribbons (JAXMED; Xing et al., 2017).
Single crystals of the title compound, suitable for X-ray analysis, were grown by slow evaporation of a dichloromethane solution.
Cg1 is the centroid of the O1/C1/N1/C5/C4 ring and Cg2 is the centroid of the C4-C9 ring. CgIÁ Á ÁCgJ is the distance between ring centroids. is the dihedral angle between the planes of the rings I and J. CgI perp and CgJ perp are the perpendicular distances of CgI from ring J and of CgJ from ring I, respectively. CgI Offset and CgJ Offset are the distances between CgI and the perpendicular projection of CgJ on ring I, and between CgJ and the perpendicular projection of CgI on ring J, respectively.

Methyl 1,3-benzoxazole-2-carboxylate
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.