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Two independent mol­ecules comprise the asymmetric unit for the title compound, C10H11N3O2, and these differ in the relative orientations of the ester side chains. Molecules associate via π–π interactions forming stacks in the crystal structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801006316/wn6014sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801006316/wn6014Isup2.hkl
Contains datablock I

CCDC reference: 165667

Comment top

We have recently reported the conversion of heterocyclylisoxazol-5(2H)-ones to imidazoles by flash vacuum pyrolysis (Prager & Singh, 1993) or photolysis (Prager et al., 1994). While these reactions, particularly the pyrolytic, proceeded in very high yields, in a few cases, we noted minor amounts of products arising from rearrangement of the initially formed carbene. For instance, the 3-nitropyridylisoxazolone (1) gave 87% of the imidazopyridine (2), and 11% of the rearranged isomer (3) (Prager & Singh, 1993).

We have now subjected the pyrimidinylisoxazolone (4), prepared by reaction of the isoxazolone (5) with 2-chloropyrimidine, to flash vacuum pyrolysis at 813 K, and have isolated a single product in high yield. Initially, we were not convinced that it was the expected imidazole (6), even though the spectral data were consistent with those of other derivatives, as the product was far less soluble than analogous compounds, was much more polar, and was strongly fluorescent. Accordingly, we have determined the structure of the product by single-crystal X-ray analysis, and have confirmed that the product was indeed the imidazole (6). Since this work was completed, (6) has been reported in a patent application in which it was incorporated into the side chain of a β-lactam (Nakai et al., 1993).

The asymmetric unit of (6) comprises two independent molecules, as illustrated in Fig. 1. The major difference between the two molecules is found in the conformation of the ester groups so that the imidazole nitrogen (N1) and carbonyl (O2) atoms are anti in molecule A and syn in molecule B. The fused ring system is effectively planar with a mean deviation of 0.002 Å for molecule A; 0.013 Å for molecule B. The side chain is coplanar with the aromatic group, as seen in the values of the O2'a—C2'a—C2a—N1a, O2a—C2'a—O2'a—C21a and C2'a—O2'a—C21a—C22a torsion angles of 176.5 (3), -4.0 (4) and 172.4 (2)°, respectively; the comparable angles for molecule B are -6.0 (5), -0.2 (5) and 168.1 (2)°, respectively.

The crystal structure is stabilized by ππ interactions. The average separation between the two five-membered ring systems of the two molecules comprising the asymmetric unit is 3.44 Å and the angle between them is 2.53 (7)°. Symmetry-related five-membered rings of molecule A are separated by 3.45 Å (symmetry code: -1 - x, 1 - y, 1 - z) and, similarly, symmetry-related six-membered rings of molecule B are separated by 3.59 Å (symmetry code: -x, 1 - y, -z). Such an arrangement leads to stacks of molecules approximately parallel to (202).

Experimental top

For the preparation of ethyl 4-methyl-5-oxo-2-(pyrimidin-2-yl)-2,5-dihydroisoxazole-3-carboxylate, (4), the isoxazolone (5) (Adembri & Tedeschi, 1965) (500 mg, 2.9 mmol) and 2-chloropyrimidine (340 mg, 0.29 mmol) were refluxed in dichloroethane (20 ml) for 16 h. The solvent was removed and the resulting solid was recrystallized from tert-butyl methyl ether to give (4) as yellow needles in 80% yield (m.p. 335–337 K). Analysis found: C 53.01, H 4.45, N 16.86%; C11H11N3O4 requires: C 52.82, H 4.47, N 16.87%. 1H NMR: δ 1.34 (t, J = 7 Hz, 3H), 4.23 (q, J = 7 Hz, 2H), 7.15 (t, J = 5 Hz, 1H), 8.64 (d, J = 5 Hz, 2H). 13C NMR: δ 7.4 (q), 13.8 (q), 62.6 (t), 109.6 (s), 118.3 (d), 148.0 (d), 156.8 (s), 158.5 (s), 159.3 (s), 168.8 (s). IR νmax: 1763, 1740, 1571, 1406, 1237 cm-1. MS m/z: 249 (M+, 100%), 204 (12), 188 (11), 176 (15), 160 (34), 133 (22), 79 (91), 67 (19), 53 (91). For the pyrolysis of (4); the isoxazolone (4) (200 mg, 0.8 mmol) was pyrolysed under FVP conditions (813 K, 393 K, 0.05 m mH g, 2 h). A solid was collected from the pyrolysis tube and recrystallized from ethanol to give colourless needles of ethyl 3-methylimidazo[1,2-a]pyrimidine-2-carboxylate, (6), in 90% yield (m.p. 468–469 K). Analysis found: C 58.54, H 5.40, N 20.48%; C9H11N3O2 requires: C 58.64, H 5.31, N 20.40%. 1H NMR: δ 1.28 (t, J = 7 Hz, 3H), 2.65 (s, 3H), 4.29 (q, J = 7 Hz, 2H), 6.90 (dd, J' = 7, J'' = 4 Hz, 1H), 8.34 (dd, J' = 7, J'' = 2 Hz, 1H), 8.46 (dd, J' = 4, J'' = 2 Hz, 1H). 13C NMR: δ 8.7 (q), 14.1 (q), 60.6 (t), 109.3 (d), 124.7 (s), 131.6 (s), 132.7 (s), 146.3 (s), 154.2 (d), 163.5 (s). IR νmax: 1702, 1503, 1196, 1086, 786, 768 cm-1. MS m/z: 205 (M+, 11%), 158 (4), 133 (100), 132 (77), 78 (14).

Refinement top

The H atoms were placed in geometrically calculated positions and included in the final refinement in the riding model approximation with an overall displacement parameter.

Computing details top

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1992); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure Corporation, 1997); program(s) used to solve structure: SIR88 (Burla et al., 1989); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The molecular structure and crystallographic numbering scheme for (6). Displacement ellipsoids are shown at the 50% probability level (Johnson, 1976).
(I) top
Crystal data top
C10H11N3O2Z = 4
Mr = 205.22F(000) = 432
Triclinic, P1Dx = 1.341 Mg m3
a = 9.910 (1) ÅMo Kα radiation, λ = 0.71073 Å
b = 11.653 (2) ÅCell parameters from 25 reflections
c = 9.000 (2) Åθ = 19.8–22.0°
α = 100.93 (1)°µ = 0.10 mm1
β = 95.31 (1)°T = 293 K
γ = 89.24 (1)°Block, colourless
V = 1016.0 (3) Å30.32 × 0.32 × 0.24 mm
Data collection top
Rigaku AFC-6R
diffractometer
Rint = 0.059
Radiation source: Rigaku rotating anodeθmax = 27.6°, θmin = 3.2°
Graphite monochromatorh = 012
ω–2θ scansk = 1515
4967 measured reflectionsl = 1111
4696 independent reflections3 standard reflections every 400 reflections
2373 reflections with I > 2σ(I) intensity decay: 5.1%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.058Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.171H-atom parameters constrained
S = 1.03 w = 1/[σ2(Fo2) + (0.0827P)2 + 0.0227P]
where P = (Fo2 + 2Fc2)/3
4696 reflections(Δ/σ)max < 0.001
272 parametersΔρmax = 0.18 e Å3
0 restraintsΔρmin = 0.31 e Å3
Crystal data top
C10H11N3O2γ = 89.24 (1)°
Mr = 205.22V = 1016.0 (3) Å3
Triclinic, P1Z = 4
a = 9.910 (1) ÅMo Kα radiation
b = 11.653 (2) ŵ = 0.10 mm1
c = 9.000 (2) ÅT = 293 K
α = 100.93 (1)°0.32 × 0.32 × 0.24 mm
β = 95.31 (1)°
Data collection top
Rigaku AFC-6R
diffractometer
Rint = 0.059
4967 measured reflections3 standard reflections every 400 reflections
4696 independent reflections intensity decay: 5.1%
2373 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0580 restraints
wR(F2) = 0.171H-atom parameters constrained
S = 1.03Δρmax = 0.18 e Å3
4696 reflectionsΔρmin = 0.31 e Å3
272 parameters
Special details top

Experimental. The scan width was (1.52 + 0.35tanθ)° with an ω scan speed of 32° per minute (up to 5 scans to achieve I/σ(I) > 20). Stationary background counts were recorded at each end of the scan, and the scan time:background time ratio was 2:1.

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 F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O2A0.5071 (2)0.14140 (17)0.3538 (2)0.0832 (6)
O2'A0.31279 (18)0.18219 (14)0.5020 (2)0.0658 (5)
O2B0.3865 (2)0.19785 (18)0.0494 (2)0.0879 (7)
O2'B0.2330 (2)0.11494 (16)0.0911 (2)0.0801 (6)
N1A0.30835 (18)0.40531 (16)0.4586 (2)0.0470 (5)
N1B0.23653 (19)0.41172 (18)0.0354 (2)0.0539 (5)
N4A0.45032 (17)0.49217 (17)0.30469 (19)0.0462 (5)
N4B0.05618 (17)0.44123 (17)0.20843 (19)0.0463 (5)
N8A0.26319 (19)0.60486 (17)0.4486 (2)0.0504 (5)
N8B0.1309 (2)0.60075 (18)0.0866 (2)0.0563 (5)
C2A0.4091 (2)0.3298 (2)0.3855 (2)0.0485 (6)
C2'A0.4171 (3)0.2096 (2)0.4099 (3)0.0580 (6)
C2B0.2039 (2)0.3120 (2)0.0920 (3)0.0498 (6)
C2'B0.2856 (3)0.2049 (2)0.0353 (3)0.0579 (6)
C3A0.4980 (2)0.3805 (2)0.2899 (2)0.0504 (6)
C3'A0.6195 (3)0.3371 (3)0.1860 (3)0.0730 (8)
H3A0.69630.38430.21520.132 (3)*
H3B0.63710.25740.19220.132 (3)*
H3C0.60370.34150.08370.132 (3)*
C3B0.0932 (2)0.3271 (2)0.1982 (2)0.0477 (6)
C3'B0.0188 (3)0.2511 (2)0.2947 (3)0.0637 (7)
H3D0.01830.28740.39980.132 (3)*
H3E0.07270.24060.26800.132 (3)*
H3F0.06320.17640.27820.132 (3)*
C5A0.4942 (2)0.5849 (2)0.2391 (3)0.0582 (7)
H5A0.57020.57850.16910.088 (2)*
C5B0.0464 (2)0.5071 (2)0.2948 (3)0.0515 (6)
H5B0.10440.47620.36440.088 (2)*
C6A0.4235 (3)0.6847 (2)0.2795 (3)0.0615 (7)
H6A0.45050.74970.23830.088 (2)*
C6B0.0605 (2)0.6178 (2)0.2757 (3)0.0567 (6)
H6B0.12900.66550.33190.088 (2)*
C7A0.3084 (3)0.6913 (2)0.3844 (3)0.0602 (7)
H7A0.26120.76170.40980.088 (2)*
C7B0.0301 (3)0.6602 (2)0.1696 (3)0.0595 (7)
H7B0.01760.73670.15710.088 (2)*
C9A0.3346 (2)0.5029 (2)0.4088 (2)0.0437 (5)
C9B0.1452 (2)0.4891 (2)0.1064 (2)0.0467 (6)
C21A0.3175 (3)0.0668 (3)0.5401 (4)0.0852 (9)
H21A0.33200.00780.44830.110 (3)*
H21B0.39110.06210.60260.110 (3)*
C21B0.3027 (3)0.0035 (3)0.0465 (4)0.0878 (10)
H21C0.32410.01440.06280.110 (3)*
H21D0.38640.00540.09500.110 (3)*
C22A0.1870 (4)0.0475 (3)0.6236 (5)0.1085 (12)
H22A0.18730.02830.65070.132 (3)*
H22B0.17370.10630.71410.132 (3)*
H22C0.11500.05190.56050.132 (3)*
C22B0.2103 (4)0.0845 (3)0.0957 (4)0.1154 (14)
H22D0.25280.16010.06870.132 (3)*
H22E0.18960.06540.20390.132 (3)*
H22F0.12820.08560.04660.132 (3)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O2A0.0802 (14)0.0689 (13)0.0963 (15)0.0273 (11)0.0163 (12)0.0147 (11)
O2'A0.0608 (11)0.0528 (10)0.0861 (13)0.0072 (8)0.0054 (10)0.0247 (9)
O2B0.0762 (14)0.0844 (14)0.0931 (15)0.0080 (11)0.0435 (12)0.0153 (12)
O2'B0.0771 (13)0.0618 (12)0.0945 (14)0.0119 (10)0.0356 (11)0.0169 (10)
N1A0.0434 (10)0.0513 (12)0.0459 (11)0.0034 (9)0.0031 (8)0.0113 (9)
N1B0.0471 (11)0.0668 (13)0.0465 (11)0.0054 (10)0.0057 (9)0.0129 (10)
N4A0.0390 (10)0.0604 (13)0.0392 (10)0.0013 (9)0.0026 (8)0.0124 (9)
N4B0.0387 (10)0.0599 (13)0.0408 (10)0.0036 (9)0.0024 (8)0.0136 (9)
N8A0.0488 (11)0.0530 (12)0.0504 (11)0.0065 (9)0.0035 (9)0.0157 (9)
N8B0.0540 (13)0.0626 (14)0.0531 (12)0.0049 (10)0.0024 (10)0.0169 (10)
C2A0.0413 (12)0.0568 (15)0.0462 (13)0.0050 (11)0.0024 (10)0.0068 (11)
C2'A0.0536 (15)0.0578 (16)0.0610 (16)0.0063 (13)0.0031 (13)0.0077 (13)
C2B0.0435 (12)0.0605 (15)0.0431 (12)0.0028 (11)0.0026 (10)0.0075 (11)
C2'B0.0530 (15)0.0673 (17)0.0504 (14)0.0046 (13)0.0080 (12)0.0097 (12)
C3A0.0393 (12)0.0689 (17)0.0409 (12)0.0043 (11)0.0019 (10)0.0056 (11)
C3'A0.0537 (16)0.096 (2)0.0622 (17)0.0135 (14)0.0177 (13)0.0075 (15)
C3B0.0408 (12)0.0593 (15)0.0430 (12)0.0009 (11)0.0013 (10)0.0118 (11)
C3'B0.0581 (16)0.0671 (17)0.0668 (16)0.0024 (13)0.0153 (13)0.0250 (13)
C5A0.0486 (14)0.083 (2)0.0459 (13)0.0132 (14)0.0010 (11)0.0229 (13)
C5B0.0404 (12)0.0674 (17)0.0460 (13)0.0004 (11)0.0046 (10)0.0131 (11)
C6A0.0622 (16)0.0680 (18)0.0605 (16)0.0083 (14)0.0026 (13)0.0296 (13)
C6B0.0495 (14)0.0631 (17)0.0566 (15)0.0017 (12)0.0008 (12)0.0113 (12)
C7A0.0613 (16)0.0625 (16)0.0606 (16)0.0023 (13)0.0044 (13)0.0218 (13)
C7B0.0575 (16)0.0611 (16)0.0610 (15)0.0054 (13)0.0049 (13)0.0145 (13)
C9A0.0363 (11)0.0580 (14)0.0366 (11)0.0001 (10)0.0026 (9)0.0109 (10)
C9B0.0416 (12)0.0610 (16)0.0366 (12)0.0061 (11)0.0014 (10)0.0097 (11)
C21A0.090 (2)0.0572 (18)0.112 (3)0.0054 (16)0.0045 (19)0.0300 (17)
C21B0.090 (2)0.069 (2)0.094 (2)0.0205 (17)0.0293 (18)0.0071 (17)
C22A0.106 (3)0.082 (2)0.145 (3)0.008 (2)0.011 (2)0.053 (2)
C22B0.139 (3)0.065 (2)0.133 (3)0.012 (2)0.043 (3)0.021 (2)
Geometric parameters (Å, º) top
O2A—C2'A1.210 (3)N8A—C7A1.307 (3)
O2'A—C2'A1.338 (3)N8A—C9A1.362 (3)
O2'A—C21A1.451 (3)N8B—C7B1.312 (3)
O2B—C2'B1.194 (3)N8B—C9B1.356 (3)
O2'B—C2'B1.326 (3)C2A—C3A1.380 (3)
O2'B—C21B1.448 (3)C2A—C2'A1.462 (3)
N1A—C9A1.314 (3)C2B—C3B1.377 (3)
N1A—C2A1.373 (3)C2B—C2'B1.477 (4)
N1B—C9B1.319 (3)C3A—C3'A1.487 (3)
N1B—C2B1.378 (3)C3B—C3'B1.496 (3)
N4A—C3A1.368 (3)C5A—C6A1.339 (4)
N4A—C5A1.373 (3)C5B—C6B1.344 (3)
N4A—C9A1.403 (3)C6A—C7A1.405 (3)
N4B—C3B1.368 (3)C6B—C7B1.404 (3)
N4B—C5B1.369 (3)C21A—C22A1.471 (4)
N4B—C9B1.401 (3)C21B—C22B1.469 (4)
C2'A—O2'A—C21A115.9 (2)O2B—C2'B—C2B125.6 (2)
C2'B—O2'B—C21B117.8 (2)O2'B—C2'B—C2B111.3 (2)
C9A—N1A—C2A104.41 (18)C2A—C3A—N4A104.53 (19)
C9B—N1B—C2B104.29 (18)C2A—C3A—C3'A133.5 (2)
C3A—N4A—C5A132.5 (2)N4A—C3A—C3'A121.9 (2)
C3A—N4A—C9A106.96 (18)C2B—C3B—N4B104.13 (19)
C5A—N4A—C9A120.5 (2)C2B—C3B—C3'B134.7 (2)
C3B—N4B—C5B131.5 (2)N4B—C3B—C3'B121.1 (2)
C3B—N4B—C9B107.67 (19)C6A—C5A—N4A117.5 (2)
C5B—N4B—C9B120.8 (2)C6B—C5B—N4B117.8 (2)
C7A—N8A—C9A116.3 (2)C5A—C6A—C7A119.9 (2)
C7B—N8B—C9B115.8 (2)C5B—C6B—C7B118.8 (2)
C3A—C2A—N1A112.4 (2)N8A—C7A—C6A124.4 (2)
C3A—C2A—C2'A125.5 (2)N8B—C7B—C6B125.3 (2)
N1A—C2A—C2'A122.0 (2)N1A—C9A—N8A126.92 (19)
O2A—C2'A—O2'A123.1 (2)N1A—C9A—N4A111.7 (2)
O2A—C2'A—C2A124.5 (2)N8A—C9A—N4A121.4 (2)
O2'A—C2'A—C2A112.4 (2)N1B—C9B—N8B127.3 (2)
C3B—C2B—N1B112.7 (2)N1B—C9B—N4B111.2 (2)
C3B—C2B—C2'B127.9 (2)N8B—C9B—N4B121.5 (2)
N1B—C2B—C2'B119.3 (2)O2'A—C21A—C22A107.6 (3)
O2B—C2'B—O2'B123.1 (3)O2'B—C21B—C22B106.6 (3)

Experimental details

Crystal data
Chemical formulaC10H11N3O2
Mr205.22
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)9.910 (1), 11.653 (2), 9.000 (2)
α, β, γ (°)100.93 (1), 95.31 (1), 89.24 (1)
V3)1016.0 (3)
Z4
Radiation typeMo Kα
µ (mm1)0.10
Crystal size (mm)0.32 × 0.32 × 0.24
Data collection
DiffractometerRigaku AFC-6R
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
4967, 4696, 2373
Rint0.059
(sin θ/λ)max1)0.652
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.058, 0.171, 1.03
No. of reflections4696
No. of parameters272
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.18, 0.31

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1992), MSC/AFC Diffractometer Control Software, TEXSAN for Windows (Molecular Structure Corporation, 1997), SIR88 (Burla et al., 1989), SHELXL97 (Sheldrick, 1997), SHELXL97.

 

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