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

Poirot, A.; Saffon-Merceron, N.; Leygue, N.; Benoist, E.; Fery-Forgues, S.

doi:10.1107/S2056989021010094

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Volume 77| Part 11| November 2021| Pages 1078-1081

https://doi.org/10.1107/S2056989021010094

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

Alexandre Poirot,^a Nathalie Saffon-Merceron,^b Nadine Leygue,^a Eric Benoist ^a and Suzanne Fery-Forgues ^a ^*

^aUniversité de Toulouse III Paul Sabatier, Laboratoire SPCMIB, UMR CNRS 5068, 118 route de Narbonne, F-31062 Toulouse, France, and ^bUniversité de Toulouse III Paul Sabatier, Institut de Chimie de Toulouse, ICT-UAR 2599, 118, route de Narbonne, F-31062 Toulouse, France
^*Correspondence e-mail: sff@chimie.ups-tlse.fr

Edited by G. Diaz de Delgado, Universidad de Los Andes, Venezuela (Received 8 July 2021; accepted 28 September 2021; online 8 October 2021)

The title compound, C₉H₇NO₃, crystallizes in the monoclinic (P2₁) space group. In the crystal, the almost planar molecules display a flattened herringbone arrangement. Stacking molecules are slipped in the lengthwise and widthwise directions and are linked by π–π interactions [d(Cg⋯Cg = 3.6640 (11) Å]. The structure is characterized by strong C—H⋯N and weak C—H⋯O hydrogen bonds, and further stabilized by C–O⋯π interactions.

Keywords: crystal structure; benzoxazole; herringbone arrangement; γ packing type; π–π interactions; strong C—H⋯N hydrogen bonds.

CCDC reference: 2112709

1. 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.

This compound was first prepared by a multi-step synthesis starting from 2,3-dioxo-1,4-benzoxazine (Dickoré et al., 1970 ) and 2-cyanobenzoxazole (Möller, 1970 ), but it can be obtained much more simply from condensation of 2-aminophenol with methyl 2,2,2-trimethoxyacetate (Musser, Hudec et al., 1984 ; Koshelev et al., 2019 ). It has been synthesized in high yields by direct carboxylation of benzoxazole using carbon dioxide (CO₂) as a naturally abundant and renewable C1 source, with (Zhang et al., 2010 ; Inomata et al., 2012 ) or without any metal catalyst (Vechorkin et al., 2010 ; Fenner & Ackermann, 2016 ). Recently, it has been produced by oxidative cyclization of glycine catalysed by copper (Liu et al., 2021 ) or induced by irradiation with visible light (Zhu et al., 2021 ). The molecule is commercially available. It has been used to complex europium, resulting in a very efficient electroluminescent layer for applications in the field of organic light-emitting diodes (OLEDs) (Koshelev et al., 2019). Used as a synthetic intermediate, methyl-1,3-benzoxazole-2-carboxylate has led to various pharmacologically active agents with anti-allergic (Musser, Brown et al., 1984 ), anti-microbial (Vodela et al., 2013 ) and neuro-anti-inflammatory (Shang et al., 2020 ) activity, to name just a few.

2. Structural commentary

The title compound (Fig. 1) crystallizes in the monoclinic space group P2₁ 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 = −6.7 (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.

Figure 1
The molecular structure of the title compound with the atom numbering. The displacement ellipsoids are drawn at the 50% probability level.

3. Supramolecular features

In the crystal structure, molecules are displayed according to the γ packing type, i.e. a flattened herringbone featuring stacks of parallel, translationally related molecules (Desiraju et al., 1989 ; Campbell et al., 2017 ) (Fig. 2). Neighboring molecules situated in almost perpendicular planes (84.4°) are linked through C—H⋯N interactions between the heterocyclic nitrogen atom N1 and H9 of an adjacent molecule and weak C—H⋯O hydrogen bonds between O2 and one hydrogen atom of the methyl group (Table 1, Fig. 2). Strong C—O⋯π interactions are also important for the stabilization of the structure (Table 2, Fig. 3). Stacking molecules are slipped in the lengthwise and widthwise directions and linked by π– π interactions [centroid–centroid distance = 3.6640 (11) Å] (Table 3).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C9—H9⋯N1ⁱ	0.95	2.53	3.377 (2)	149
C3—H3C⋯O2ⁱⁱ	0.98	2.65	3.389 (2)	133
Symmetry codes: (i) ; (ii) $[-x+1, y+{\script{1\over 2}}, -z+1]$ .

Table 2
C—O⋯π interactions (Å, °)

Cg1 is the centroid of the O1/C1/N1/C5/C4 ring and Cg3 is the centroid of the O1/C1/C5–C9 ring.

X	I	J	I⋯J	X⋯J	X—I⋯J
C2	O2	Cg1ⁱⁱ	3.2088 (14)	3.5487 (18)	96.39 (10)
C2	O2	Cg3ⁱⁱ	3.5912 (14)	3.7321 (17)	87.29 (10)
Symmetry code: (ii) x, −1 + y, z.

Table 3
π–π interaction (Å, °)

Cg1 is the centroid of the O1/C1/N1/C5/C4 ring and Cg2 is the centroid of the C4–C9 ring. CgI⋯CgJ is the distance between ring centroids. α 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.

I	J	CgI⋯CgJ	α	CgI_perp	CgJ_perp	CgI_Offset	CgJ_Offset
1	2ⁱⁱ	3.6640 (11)	0.19 (9)	3.3115 (7)	3.3065 (8)	1.579	1.568
Symmetry code: (ii) x, −1 + y, z.

Figure 2
C—H⋯N and C—H⋯O hydrogen bonds (blue dotted lines).

Figure 3
π–π and C—O⋯π interactions (green dotted lines). Orange balls represent the ring centroids Cg.

4. 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; Piątek 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).

5. Synthesis and crystallization

The title compound was synthesized according to a variant of the procedure described by Jacobs et al. (2017 ) (Fig. 4). To a mixture of 5-aminophenol (1.09 g, 0.01 mol) and triethylamine (2.02 g, 0.02 mol) in anhydrous tetrahydrofuran (40 mL) at 263 K was added slowly methyl oxalyl chloride (1.34 g, 0.011 mol). The mixture was stirred at room temperature for 3 h and then cooled onto an ice–water bath. Triphenylphosphine (5.64 g, 0.0215 mol), diisopropyl azodicarboxylate (2.25 g, 0.011 mol) and tetrahydrofuran (50 mL) were then added. The solution was allowed to stir at room temperature for 16 h and concentrated in vacuo. The crude product was purified by column chromatography (SiO₂, petroleum ether/dichloromethane 70/30 v/v until 60/40 v/v) to give a white solid (1.2 g) in 83% yield. ¹H NMR (300 MHz, CDCl₃): δ = 7.90 (ddd, J = 7.9, 1.5, 0.8 Hz, 1H), 7.67 (ddd, J = 8.1, 1.2, 0.8 Hz, 1H), 7.57–7.44 (m, 2H), 4.10 (s, 3H). ¹³C NMR (75 MHz, CDCl₃): δ = 156.9, 152.5, 150.9, 140.5, 128.2, 125.8, 122.2, 111.7, 53.7.

Figure 4
Synthesis route to methyl-1,3-benzoxazole-2-carboxylate.

Single crystals of the title compound, suitable for X-ray analysis, were grown by slow evaporation of a dichloromethane solution.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms were fixed geometrically and treated as riding atoms with C—H = 0.95 Å (aromatic) or 0.98 Å (CH₃), with U_iso(H) = 1.2U_eq(C) or 1.5U_eq(CH₃).

Table 4
Experimental details

Crystal data
Chemical formula	C₉H₇NO₃
M_r	177.16
Crystal system, space group	Monoclinic, P2₁
Temperature (K)	193
a, b, c (Å)	6.8165 (3), 4.4676 (2), 13.2879 (6)
β (°)	95.1319 (16)
V (Å³)	403.04 (3)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	0.11
Crystal size (mm)	0.40 × 0.30 × 0.10

Data collection
Diffractometer	Bruker D8-Venture Photon III detector
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.698, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	9084, 1954, 1860
R_int	0.022
(sin θ/λ)_max (Å⁻¹)	0.667

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.030, 0.077, 1.10
No. of reflections	1954
No. of parameters	119
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.20, −0.16
Computer programs: APEX3 and SAINT (Bruker, 2018 ), SHELXT (Sheldrick, 2015a ), SHELXL2018/3 (Sheldrick, 2015b ), SHELXTL (Sheldrick, 2008 ), Mercury (Macrae et al., 2020 ), PLATON (Spek 2020 ) and publCIF (Westrip 2010 ).

Supporting information

CCDC reference: 2112709

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989021010094/dj2033sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989021010094/dj2033Isup3.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989021010094/dj2033Isup4.cml

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2018); cell refinement: SAINT (Bruker, 2018); data reduction: SAINT (Bruker, 2018); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2020); software used to prepare material for publication: PLATON (Spek 2020) and publCIF (Westrip 2010).

Methyl 1,3-benzoxazole-2-carboxylate top

Crystal data top

C₉H₇NO₃	F(000) = 184
M_r = 177.16	D_x = 1.460 Mg m⁻³
Monoclinic, P2₁	Mo Kα radiation, λ = 0.71073 Å
a = 6.8165 (3) Å	Cell parameters from 6695 reflections
b = 4.4676 (2) Å	θ = 3.3–28.2°
c = 13.2879 (6) Å	µ = 0.11 mm⁻¹
β = 95.1319 (16)°	T = 193 K
V = 403.04 (3) Å³	Plate, colourless
Z = 2	0.40 × 0.30 × 0.10 mm

Data collection top

Bruker D8-Venture Photon III detector diffractometer	1860 reflections with I > 2σ(I)
Radiation source: Fine-focus sealed tube	R_int = 0.022
Phi and ω scans	θ_max = 28.3°, θ_min = 3.3°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −8→9
T_min = 0.698, T_max = 0.746	k = −5→5
9084 measured reflections	l = −17→17
1954 independent reflections

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.030	H-atom parameters constrained
wR(F²) = 0.077	w = 1/[σ²(F_o²) + (0.0432P)² + 0.0403P] where P = (F_o² + 2F_c²)/3
S = 1.10	(Δ/σ)_max < 0.001
1954 reflections	Δρ_max = 0.20 e Å⁻³
119 parameters	Δρ_min = −0.16 e Å⁻³
1 restraint

Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.25255 (16)	0.3885 (3)	0.69933 (9)	0.0329 (3)
O2	0.43981 (19)	−0.0004 (3)	0.57993 (9)	0.0382 (3)
O3	0.73220 (17)	0.2017 (3)	0.63833 (9)	0.0341 (3)
N1	0.54541 (19)	0.5493 (3)	0.77177 (10)	0.0277 (3)
C1	0.4528 (2)	0.3789 (4)	0.70473 (12)	0.0296 (3)
C2	0.5378 (2)	0.1703 (4)	0.63294 (12)	0.0297 (3)
C3	0.8319 (3)	0.0125 (4)	0.57015 (13)	0.0381 (4)
H3A	0.794777	−0.196824	0.579791	0.057*
H3B	0.974729	0.034297	0.584461	0.057*
H3C	0.793506	0.072127	0.500188	0.057*
C4	0.2149 (2)	0.5919 (4)	0.77264 (12)	0.0291 (3)
C5	0.3947 (2)	0.6919 (4)	0.81779 (11)	0.0273 (3)
C6	0.4014 (2)	0.9009 (4)	0.89607 (13)	0.0347 (4)
H6	0.522730	0.971603	0.928121	0.042*
C7	0.2220 (3)	0.9998 (4)	0.92465 (14)	0.0401 (4)
H7	0.220300	1.141802	0.977785	0.048*
C8	0.0429 (3)	0.8959 (5)	0.87719 (15)	0.0406 (4)
H8	−0.076652	0.971435	0.898830	0.049*
C9	0.0342 (2)	0.6878 (5)	0.80018 (14)	0.0370 (4)
H9	−0.087048	0.615698	0.768384	0.044*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0259 (5)	0.0362 (6)	0.0359 (6)	−0.0064 (5)	−0.0013 (4)	0.0001 (5)
O2	0.0406 (6)	0.0349 (6)	0.0380 (6)	−0.0087 (5)	−0.0024 (5)	−0.0035 (5)
O3	0.0315 (6)	0.0342 (6)	0.0364 (6)	−0.0025 (5)	0.0009 (4)	−0.0061 (5)
N1	0.0241 (6)	0.0274 (6)	0.0312 (6)	−0.0017 (5)	0.0008 (4)	0.0002 (5)
C1	0.0288 (7)	0.0286 (7)	0.0311 (7)	−0.0048 (6)	0.0007 (6)	0.0048 (6)
C2	0.0329 (8)	0.0264 (7)	0.0292 (7)	−0.0042 (6)	−0.0006 (6)	0.0039 (6)
C3	0.0384 (9)	0.0380 (10)	0.0381 (8)	0.0030 (8)	0.0047 (7)	−0.0042 (8)
C4	0.0259 (7)	0.0305 (8)	0.0308 (7)	−0.0049 (6)	0.0010 (5)	0.0063 (6)
C5	0.0233 (7)	0.0278 (7)	0.0306 (7)	−0.0019 (6)	0.0013 (5)	0.0057 (6)
C6	0.0311 (8)	0.0357 (8)	0.0366 (8)	−0.0030 (7)	−0.0006 (6)	−0.0014 (7)
C7	0.0438 (10)	0.0370 (9)	0.0407 (9)	0.0020 (8)	0.0096 (7)	−0.0015 (8)
C8	0.0302 (8)	0.0431 (10)	0.0505 (10)	0.0040 (8)	0.0146 (7)	0.0107 (9)
C9	0.0220 (7)	0.0429 (9)	0.0461 (9)	−0.0035 (7)	0.0032 (6)	0.0104 (8)

Geometric parameters (Å, º) top

O1—C1	1.3610 (19)	C4—C9	1.384 (2)
O1—C4	1.373 (2)	C4—C5	1.390 (2)
O2—C2	1.200 (2)	C5—C6	1.395 (2)
O3—C2	1.3281 (19)	C6—C7	1.385 (3)
O3—C3	1.452 (2)	C6—H6	0.9500
N1—C1	1.293 (2)	C7—C8	1.402 (3)
N1—C5	1.395 (2)	C7—H7	0.9500
C1—C2	1.488 (2)	C8—C9	1.380 (3)
C3—H3A	0.9800	C8—H8	0.9500
C3—H3B	0.9800	C9—H9	0.9500
C3—H3C	0.9800

C1—O1—C4	103.51 (12)	C9—C4—C5	123.92 (17)
C2—O3—C3	115.17 (14)	C4—C5—N1	108.64 (15)
C1—N1—C5	103.74 (13)	C4—C5—C6	120.36 (15)
N1—C1—O1	116.33 (15)	N1—C5—C6	131.00 (14)
N1—C1—C2	128.06 (14)	C7—C6—C5	116.58 (16)
O1—C1—C2	115.61 (13)	C7—C6—H6	121.7
O2—C2—O3	126.82 (17)	C5—C6—H6	121.7
O2—C2—C1	123.11 (16)	C6—C7—C8	121.71 (18)
O3—C2—C1	110.07 (14)	C6—C7—H7	119.1
O3—C3—H3A	109.5	C8—C7—H7	119.1
O3—C3—H3B	109.5	C9—C8—C7	122.32 (17)
H3A—C3—H3B	109.5	C9—C8—H8	118.8
O3—C3—H3C	109.5	C7—C8—H8	118.8
H3A—C3—H3C	109.5	C8—C9—C4	115.10 (16)
H3B—C3—H3C	109.5	C8—C9—H9	122.4
O1—C4—C9	128.30 (15)	C4—C9—H9	122.4
O1—C4—C5	107.78 (14)

C5—N1—C1—O1	0.05 (19)	C9—C4—C5—N1	179.93 (15)
C5—N1—C1—C2	−179.34 (15)	O1—C4—C5—C6	−179.61 (14)
C4—O1—C1—N1	0.03 (18)	C9—C4—C5—C6	0.2 (2)
C4—O1—C1—C2	179.50 (13)	C1—N1—C5—C4	−0.11 (17)
C3—O3—C2—O2	1.7 (2)	C1—N1—C5—C6	179.60 (17)
C3—O3—C2—C1	−178.99 (13)	C4—C5—C6—C7	−0.2 (2)
N1—C1—C2—O2	172.61 (18)	N1—C5—C6—C7	−179.92 (16)
O1—C1—C2—O2	−6.8 (2)	C5—C6—C7—C8	−0.1 (3)
N1—C1—C2—O3	−6.7 (2)	C6—C7—C8—C9	0.6 (3)
O1—C1—C2—O3	173.92 (14)	C7—C8—C9—C4	−0.6 (3)
C1—O1—C4—C9	−179.89 (17)	O1—C4—C9—C8	180.00 (16)
C1—O1—C4—C5	−0.10 (16)	C5—C4—C9—C8	0.2 (3)
O1—C4—C5—N1	0.14 (17)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C9—H9···N1ⁱ	0.95	2.53	3.377 (2)	149
C3—H3C···O2ⁱⁱ	0.98	2.65	3.389 (2)	133

Symmetry codes: (i) x−1, y, z; (ii) −x+1, y+1/2, −z+1.

C—O···π interactions (Å, °) top

Cg1 is the centroid of the O1/C1/N1/C5/C4 ring and Cg3 is the centroid of the O1/C1/C5–C9 ring.

X	I	J	I···J	X···J	X—I···J
C2	O2	Cg1ⁱⁱ	3.2088 (14)	3.5487 (18)	96.39 (10)
C2	O2	Cg3ⁱⁱ	3.5912 (14)	3.7321 (17)	87.29 (10)

Symmetry code: (ii) x, -1 + y, z.

π–π interaction (Å, °) top

Cg1 is the centroid of the O1/C1/N1/C4/C5 ring and Cg2 is the centroid of the C4–C9 ring. CgI···CgJ is the distance between ring centroids. The dihedral angle is that 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.

I	J	CgI···CgJ	Dihedral angle	CgI_perp	CgJ_perp	CgI_Offset	CgJ_Offset
1	2ⁱⁱ	3.6640 (11)	0.19 (9)	3.3115 (7)	3.3065 (8)	1.579	1.568

Symmetry code: (ii) x, -1 + y, z.

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Volume 77| Part 11| November 2021| Pages 1078-1081

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