Acta Cryst. (2008). E64, o602 [ doi:10.1107/S1600536808004376 ]
The title compound, C6H9NO4, was prepared stereoselectively as a precursor for 1-azadienes in a study of hetero-Diels-Alder reactions. The configuration of the C=N double bond was found to be Z, corroborating earlier assignments of similar compounds based only on NMR and IR spectroscopic analysis.
A stirred solution of 7.25 g (50.0 mmol) of Z-Methyl 2-(hydroxyimino)-3-oxobutanoate (Lu & Arndt, 2007; Fletcher et al., 2006) in anhydrous acetone (50 ml) was cooled to 273 K and potassium carbonate (3.8 g, 27.5 mmol) was added, followed by dimethyl sulfate (5.70 ml, 60.0 mmol). The stirred reaction mixture was warmed to room temperature over 2 h and kept stirring for 10 h (TLC control). The reaction mixture was filtered and the solid residue was rinsed with acetone (3 × 10 ml). The combined filtrates were evaporated to dryness, redissolved in Et2O (100 ml), washed with sat. NaCl solution (3 × 40 ml) and dried with Na2SO4. Concentration and purification by column chromatography (100 g SiO2, EtOAc/light petroleum v/v = 1:8) gave 7.60 g (47.8 mmol, 96%) of the title compound as a colourless oil which crystallized on standing as colourless cubes.
Mp = 335–337 K; Rf = 0.46 (SiO2, EtOAc/cyclohexane = 1:2); 1H NMR (400 MHz, CDCl3) δ = 2.38 (3H, s, C(O)CH3), 3.85 (3H, s, =NOCH3), 4.08 (3H, s, COOCH3); 13C NMR (100.6 MHz, CDCl3) δ = 25.1 (C(O)CH3), 52.5 (COOCH3), 64.4 (NOCH3), 149.9 (C=N), 161.5 (COOCH3), 192.7 (C(O)CH3); IR (KBr): ν = 3009w, 2951w, 1744 s, 1683 s, 1596 s, 1241 s, 1021 s, 841 s cm-1; HRMS (EI): m/Z calc. for C6H9NO4 [M+]: 159.0532, found: 159.0524.
Anomalous dispersion was negligible and Friedel pairs were merged before refinement.
The H atoms were placed in calculated positions, with C—H = 0.96 Å and were refined as riding, with Uiso(H) = 1.5Ueq(C); the methyl groups were allowed to rotate but not to tip.
Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO and SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2003).
![[Figure 1]](./hb2698fig1thm.gif)
| Fig. 1. The molecular structure of (I) with displacement ellipsoids shown at the 30% probability level (arbitrary spheres for the H atoms). |
| C6H9NO4 | F000 = 336 |
| Mr = 159.14 | Dx = 1.296 Mg m−3 |
| Orthorhombic, Pna21 | Mo Kα radiation λ = 0.71073 Å |
| Hall symbol: P 2c -2n | Cell parameters from 3104 reflections |
| a = 8.3410 (17) Å | θ = 3.0–27.5º |
| b = 13.410 (3) Å | µ = 0.11 mm−1 |
| c = 7.2900 (15) Å | T = 291 (1) K |
| V = 815.4 (3) Å3 | Cube, colourless |
| Z = 4 | 0.2 × 0.2 × 0.2 mm |
| Nonius KappaCCD diffractometer | 899 independent reflections |
| Radiation source: fine-focus sealed tube | 536 reflections with I > 2σ(I) |
| Monochromator: graphite | Rint = 0.045 |
| Detector resolution: 19 vertical, 18 horizontal pixels mm-1 | θmax = 26.4º |
| T = 291(1) K | θmin = 3.9º |
| 213 frames via ω–rotation (Δω = 1%) and two times 40 s per frame (four sets at different κ–angles) scans | h = −10→10 |
| Absorption correction: none | k = −16→16 |
| 3104 measured reflections | l = −9→9 |
| Refinement on F2 | Secondary atom site location: difference Fourier map |
| Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
| R[F2 > 2σ(F2)] = 0.027 | H-atom parameters constrained |
| wR(F2) = 0.057 | w = 1/[σ2(Fo2) + (0.0206P)2] where P = (Fo2 + 2Fc2)/3 |
| S = 1.09 | (Δ/σ)max < 0.001 |
| 899 reflections | Δρmax = 0.08 e Å−3 |
| 104 parameters | Δρmin = −0.11 e Å−3 |
| 1 restraint | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.087 (6) |
| C6H9NO4 | V = 815.4 (3) Å3 |
| Mr = 159.14 | Z = 4 |
| Orthorhombic, Pna21 | Mo Kα |
| a = 8.3410 (17) Å | µ = 0.11 mm−1 |
| b = 13.410 (3) Å | T = 291 (1) K |
| c = 7.2900 (15) Å | 0.2 × 0.2 × 0.2 mm |
| Nonius KappaCCD diffractometer | 899 independent reflections |
| Absorption correction: none | 536 reflections with I > 2σ(I) |
| 3104 measured reflections | Rint = 0.045 |
| R[F2 > 2σ(F2)] = 0.027 | H-atom parameters constrained |
| wR(F2) = 0.057 | Δρmax = 0.08 e Å−3 |
| S = 1.09 | Δρmin = −0.11 e Å−3 |
| 899 reflections | Absolute structure: ? |
| 104 parameters | Flack parameter: ? |
| 1 restraint | Rogers parameter: ? |
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. |
| x | y | z | Uiso*/Ueq | ||
| O1 | 0.14686 (19) | 0.12432 (11) | 0.8457 (2) | 0.0633 (5) | |
| O2 | 0.1931 (2) | 0.03995 (12) | 0.4285 (2) | 0.0784 (6) | |
| O3 | 0.4017 (2) | 0.23981 (12) | 0.3446 (3) | 0.0923 (7) | |
| O4 | 0.4114 (2) | 0.03491 (11) | 0.6049 (2) | 0.0634 (5) | |
| N1 | 0.19750 (19) | 0.20788 (12) | 0.7495 (3) | 0.0536 (5) | |
| C1 | 0.2847 (3) | 0.07762 (15) | 0.5349 (3) | 0.0520 (6) | |
| C3 | 0.2673 (2) | 0.18321 (15) | 0.5998 (3) | 0.0463 (5) | |
| C5 | 0.3291 (3) | 0.26405 (17) | 0.4804 (3) | 0.0557 (6) | |
| C7 | 0.0702 (3) | 0.15466 (19) | 1.0136 (3) | 0.0749 (8) | |
| H7A | 0.0349 | 0.0967 | 1.0796 | 0.112* | |
| H7B | −0.0205 | 0.1961 | 0.9857 | 0.112* | |
| H7C | 0.1449 | 0.1914 | 1.0875 | 0.112* | |
| C8 | 0.4383 (4) | −0.06865 (16) | 0.5537 (3) | 0.0819 (9) | |
| H8A | 0.5226 | −0.0960 | 0.6279 | 0.123* | |
| H8D | 0.4683 | −0.0721 | 0.4268 | 0.123* | |
| H8B | 0.3416 | −0.1061 | 0.5727 | 0.123* | |
| C9 | 0.3008 (3) | 0.37018 (15) | 0.5307 (4) | 0.0674 (7) | |
| H9A | 0.3481 | 0.4128 | 0.4397 | 0.101* | |
| H9B | 0.3484 | 0.3836 | 0.6480 | 0.101* | |
| H9D | 0.1875 | 0.3826 | 0.5367 | 0.101* |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| O1 | 0.0881 (11) | 0.0498 (9) | 0.0519 (9) | −0.0045 (8) | 0.0208 (9) | 0.0002 (9) |
| O2 | 0.0868 (13) | 0.0657 (11) | 0.0828 (13) | 0.0028 (9) | −0.0205 (12) | −0.0202 (11) |
| O3 | 0.1322 (17) | 0.0691 (12) | 0.0755 (13) | −0.0101 (10) | 0.0492 (14) | −0.0068 (11) |
| O4 | 0.0676 (10) | 0.0551 (9) | 0.0675 (10) | 0.0137 (8) | −0.0078 (9) | −0.0037 (9) |
| N1 | 0.0625 (12) | 0.0471 (11) | 0.0510 (12) | −0.0028 (9) | 0.0046 (12) | 0.0004 (10) |
| C1 | 0.0601 (14) | 0.0494 (13) | 0.0467 (14) | −0.0018 (13) | 0.0041 (14) | −0.0023 (13) |
| C3 | 0.0483 (12) | 0.0491 (13) | 0.0415 (12) | 0.0010 (10) | −0.0001 (12) | −0.0037 (12) |
| C5 | 0.0615 (16) | 0.0567 (15) | 0.0490 (14) | −0.0031 (12) | 0.0063 (13) | −0.0008 (13) |
| C7 | 0.0981 (19) | 0.0731 (17) | 0.0535 (16) | −0.0063 (16) | 0.0276 (15) | −0.0040 (14) |
| C8 | 0.1075 (19) | 0.0597 (17) | 0.079 (2) | 0.0278 (14) | 0.0040 (16) | 0.0008 (15) |
| C9 | 0.0773 (15) | 0.0517 (14) | 0.0732 (17) | −0.0057 (13) | 0.0087 (13) | 0.0009 (15) |
| O1—N1 | 1.387 (2) | C7—H7A | 0.9600 |
| O1—C7 | 1.440 (3) | C7—H7B | 0.9600 |
| O2—C1 | 1.200 (3) | C7—H7C | 0.9600 |
| O3—C5 | 1.205 (3) | C8—H8A | 0.9600 |
| O4—C1 | 1.306 (3) | C8—H8D | 0.9600 |
| O4—C8 | 1.455 (2) | C8—H8B | 0.9600 |
| N1—C3 | 1.281 (3) | C9—H9A | 0.9600 |
| C1—C3 | 1.500 (3) | C9—H9B | 0.9600 |
| C3—C5 | 1.483 (3) | C9—H9D | 0.9600 |
| C5—C9 | 1.489 (3) | ||
| N1—O1—C7 | 109.67 (16) | O1—C7—H7C | 109.5 |
| C1—O4—C8 | 116.29 (19) | H7A—C7—H7C | 109.5 |
| C3—N1—O1 | 111.12 (17) | H7B—C7—H7C | 109.5 |
| O2—C1—O4 | 125.7 (2) | O4—C8—H8A | 109.5 |
| O2—C1—C3 | 122.6 (2) | O4—C8—H8D | 109.5 |
| O4—C1—C3 | 111.7 (2) | H8A—C8—H8D | 109.5 |
| N1—C3—C5 | 118.01 (19) | O4—C8—H8B | 109.5 |
| N1—C3—C1 | 123.8 (2) | H8A—C8—H8B | 109.5 |
| C5—C3—C1 | 118.1 (2) | H8D—C8—H8B | 109.5 |
| O3—C5—C3 | 117.4 (2) | C5—C9—H9A | 109.5 |
| O3—C5—C9 | 122.7 (2) | C5—C9—H9B | 109.5 |
| C3—C5—C9 | 119.9 (2) | H9A—C9—H9B | 109.5 |
| O1—C7—H7A | 109.5 | C5—C9—H9D | 109.5 |
| O1—C7—H7B | 109.5 | H9A—C9—H9D | 109.5 |
| H7A—C7—H7B | 109.5 | H9B—C9—H9D | 109.5 |
Funding by the Deutsche Forschungsgemeinschaft (Emmy–Noether grant Nos. AR493–1 and -2 to HDA), the Fonds der Chemischen Industrie, and the IMPRS Chemical Biology (to JYL and WZS) is gratefully acknowledged.
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Oxime geometry has been found to be important for determining their reactivity in cycloadditions and pericyclic reactions (e.g. François et al., 2004). The title compound, (I), was prepared in the study of hetero-Diels–Alder reactions to form 3-hydroxy-pyridines (Lu & Arndt, 2007; Fletcher et al., 2006).
The crystal structure of (I) (Fig. 1) verifies earlier studies by NMR and IR (Buehler, 1967; Karabatsos & Taller, 1968; Levy & Nelson, 1972; Jirman et al., 1990; Corrêa & Moran, 1999) of Z-configured oximes and forms a basis for further studies in the field. Interestingly, the C1/O2/O4 carboxyl group in (I) adopts a dihedral angle of 93° with respect to the coplanar N?C—C?O π-system, which indicates complete absence of electronic conjugation.