Dimethyl 2-{[2-(methoxycarbonyl)-1-(methoxycarbonylmethyl)pyrrol-4-yl]methylene}propanedioate
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101008204/jz1455sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270101008204/jz1455Isup2.hkl |
CCDC reference: 170201
For related literature, see: Bartell et al. (1965); Gribble (1996); Lokaj et al. (2001); Nygaard et al. (1969); Shmueli et al. (1973).
To a stirred solution of methyl (4-formyl-2-methoxycarbonylpyrrolyl)acetate (10 mmol) prepared previously (Lokaj et al., 2001) in 20 ml of TMF was added at once sodium dimethylmalonate (prepared freshly from dimethylmalonate and sodium hydride) in 15 ml of TMF. The reaction was quickly quenched with a saturated aqueous solution of ammonium chloride, extracted with diethyl ether, dried with sodium sulfate and evaporated to dryness. Then the remaining dimethylmalonate was evaporated using a high-vacuum pump (0.1 Pa) and the residue crystallized from diethyl ether/n-pentane (m.p. 410–412 K).
Although most of the H atoms were seen in a difference Fourier map, they were refined with fixed geometry, riding on their carrier atoms, with Uiso set to 1.2 (or 1.5 for the methyl H atoms) times Ueq of the parent atom. The methyl groups were allowed to rotate about their local threefold axis.
Data collection: Syntex software (Syntex, 1973); cell refinement: Syntex software; data reduction: XP21 (Pavelčík, 1987); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.
Fig. 1. A view of the title molecule showing the labelling of the non-H atoms. Displacement ellipsoids are shown at 30% probability level and H atoms are drawn as small circles of arbitrary radius. |
C15H17NO8 | Dx = 1.347 Mg m−3 Dm = 1.35 (1) Mg m−3 Dm measured by flotation in bromoform/c-hexane |
Mr = 339.30 | Melting point: 411 K |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 9.906 (4) Å | Cell parameters from 15 reflections |
b = 12.528 (5) Å | θ = 8–17° |
c = 13.991 (5) Å | µ = 0.11 mm−1 |
β = 105.44 (4)° | T = 293 K |
V = 1673.7 (11) Å3 | Plate, colourless |
Z = 4 | 0.35 × 0.30 × 0.10 mm |
F(000) = 712 |
Syntex P21 diffractometer | Rint = 0.037 |
Radiation source: fine-focus sealed tube | θmax = 25.0°, θmin = 2.7° |
Graphite monochromator | h = −11→0 |
θ/2θ scans | k = −14→0 |
3064 measured reflections | l = −16→16 |
2883 independent reflections | 2 standard reflections every 98 reflections |
1837 reflections with I > 2σ(I) | intensity decay: 2% |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.059 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.197 | Riding |
S = 1.00 | w = 1/[σ2(Fo2) + (0.1083P)2] where P = (Fo2 + 2Fc2)/3 |
2883 reflections | (Δ/σ)max = 0.002 |
221 parameters | Δρmax = 0.23 e Å−3 |
0 restraints | Δρmin = −0.18 e Å−3 |
C15H17NO8 | V = 1673.7 (11) Å3 |
Mr = 339.30 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 9.906 (4) Å | µ = 0.11 mm−1 |
b = 12.528 (5) Å | T = 293 K |
c = 13.991 (5) Å | 0.35 × 0.30 × 0.10 mm |
β = 105.44 (4)° |
Syntex P21 diffractometer | Rint = 0.037 |
3064 measured reflections | 2 standard reflections every 98 reflections |
2883 independent reflections | intensity decay: 2% |
1837 reflections with I > 2σ(I) |
R[F2 > 2σ(F2)] = 0.059 | 0 restraints |
wR(F2) = 0.197 | Riding |
S = 1.00 | Δρmax = 0.23 e Å−3 |
2883 reflections | Δρmin = −0.18 e Å−3 |
221 parameters |
x | y | z | Uiso*/Ueq | ||
N1 | −0.1372 (2) | 0.13077 (19) | 0.59636 (18) | 0.0661 (7) | |
C2 | 0.0084 (3) | 0.1083 (2) | 0.6196 (2) | 0.0634 (7) | |
C3 | 0.0218 (3) | −0.0002 (2) | 0.62588 (19) | 0.0602 (7) | |
H3 | 0.1059 | −0.0375 | 0.6392 | 0.072* | |
C4 | −0.1144 (3) | −0.0473 (2) | 0.60868 (19) | 0.0557 (7) | |
C5 | −0.2090 (3) | 0.0374 (2) | 0.5890 (2) | 0.0646 (8) | |
H5 | −0.3060 | 0.0311 | 0.5734 | 0.078* | |
C6 | −0.2020 (3) | 0.2372 (2) | 0.5814 (2) | 0.0645 (8) | |
H6A | −0.1574 | 0.2829 | 0.6368 | 0.077* | |
H6B | −0.3004 | 0.2313 | 0.5792 | 0.077* | |
C7 | −0.1875 (3) | 0.2869 (2) | 0.4857 (2) | 0.0610 (7) | |
O8 | −0.1687 (2) | 0.23988 (18) | 0.41503 (16) | 0.0775 (6) | |
O9 | −0.2007 (2) | 0.39301 (16) | 0.48993 (16) | 0.0778 (6) | |
C10 | −0.1805 (5) | 0.4537 (3) | 0.4061 (3) | 0.1008 (12) | |
H10A | −0.1839 | 0.5286 | 0.4195 | 0.151* | |
H10B | −0.2533 | 0.4361 | 0.3477 | 0.151* | |
H10C | −0.0911 | 0.4363 | 0.3957 | 0.151* | |
C11 | 0.1130 (3) | 0.1929 (2) | 0.6296 (2) | 0.0634 (7) | |
O12 | 0.0870 (2) | 0.28645 (18) | 0.61594 (18) | 0.0885 (7) | |
O13 | 0.2428 (2) | 0.15240 (15) | 0.65611 (16) | 0.0718 (6) | |
C14 | 0.3556 (3) | 0.2324 (3) | 0.6720 (3) | 0.0883 (10) | |
H14A | 0.4443 | 0.1981 | 0.6989 | 0.133* | |
H14B | 0.3412 | 0.2857 | 0.7176 | 0.133* | |
H14C | 0.3547 | 0.2654 | 0.6100 | 0.133* | |
C15 | −0.1410 (3) | −0.1606 (2) | 0.6151 (2) | 0.0612 (7) | |
H15 | −0.0639 | −0.2047 | 0.6202 | 0.073* | |
C16 | −0.2598 (3) | −0.2109 (2) | 0.6149 (2) | 0.0614 (7) | |
C17 | −0.3979 (3) | −0.1538 (2) | 0.6029 (2) | 0.0634 (7) | |
O18 | −0.4825 (2) | −0.13889 (18) | 0.52388 (17) | 0.0853 (7) | |
O19 | −0.4141 (2) | −0.12245 (17) | 0.68969 (15) | 0.0768 (6) | |
C20 | −0.5433 (4) | −0.0646 (3) | 0.6862 (3) | 0.0934 (11) | |
H20A | −0.5433 | −0.0427 | 0.7519 | 0.140* | |
H20B | −0.6222 | −0.1103 | 0.6597 | 0.140* | |
H20C | −0.5494 | −0.0029 | 0.6447 | 0.140* | |
C21 | −0.2585 (3) | −0.3296 (2) | 0.6261 (2) | 0.0657 (8) | |
O22 | −0.1547 (2) | −0.38419 (18) | 0.6431 (2) | 0.0980 (9) | |
O23 | −0.3874 (2) | −0.36713 (16) | 0.62029 (18) | 0.0809 (7) | |
C24 | −0.3958 (4) | −0.4819 (2) | 0.6340 (3) | 0.0881 (10) | |
H24A | −0.4919 | −0.5022 | 0.6250 | 0.132* | |
H24B | −0.3426 | −0.5008 | 0.6998 | 0.132* | |
H24C | −0.3586 | −0.5185 | 0.5864 | 0.132* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0551 (14) | 0.0702 (16) | 0.0712 (15) | 0.0083 (12) | 0.0139 (11) | 0.0047 (11) |
C2 | 0.0516 (16) | 0.0723 (18) | 0.0636 (17) | 0.0062 (14) | 0.0109 (13) | 0.0037 (13) |
C3 | 0.0574 (17) | 0.0643 (18) | 0.0593 (16) | 0.0036 (13) | 0.0161 (13) | 0.0046 (12) |
C4 | 0.0457 (14) | 0.0630 (16) | 0.0562 (14) | 0.0080 (12) | 0.0098 (12) | 0.0058 (12) |
C5 | 0.0611 (17) | 0.0661 (18) | 0.0643 (17) | 0.0010 (14) | 0.0127 (14) | −0.0020 (13) |
C6 | 0.0651 (18) | 0.0544 (16) | 0.0742 (18) | 0.0025 (13) | 0.0189 (15) | 0.0027 (12) |
C7 | 0.0565 (16) | 0.0506 (16) | 0.0738 (19) | 0.0044 (12) | 0.0134 (14) | 0.0075 (13) |
O8 | 0.0826 (15) | 0.0781 (15) | 0.0743 (13) | −0.0006 (11) | 0.0249 (12) | −0.0044 (11) |
O9 | 0.0930 (16) | 0.0580 (12) | 0.0848 (14) | 0.0073 (11) | 0.0279 (12) | 0.0055 (10) |
C10 | 0.130 (3) | 0.073 (2) | 0.110 (3) | 0.012 (2) | 0.049 (3) | 0.0248 (19) |
C11 | 0.0562 (17) | 0.0620 (18) | 0.0729 (18) | 0.0063 (14) | 0.0183 (14) | 0.0026 (14) |
O12 | 0.0713 (14) | 0.0657 (14) | 0.124 (2) | 0.0052 (11) | 0.0177 (13) | 0.0103 (12) |
O13 | 0.0572 (12) | 0.0666 (13) | 0.0855 (14) | −0.0003 (10) | 0.0088 (10) | −0.0014 (10) |
C14 | 0.063 (2) | 0.102 (3) | 0.093 (2) | −0.0203 (18) | 0.0091 (18) | −0.0061 (19) |
C15 | 0.0535 (16) | 0.0565 (16) | 0.0681 (17) | 0.0061 (13) | 0.0065 (13) | 0.0057 (13) |
C16 | 0.0578 (17) | 0.0559 (16) | 0.0659 (17) | 0.0089 (13) | 0.0083 (14) | 0.0016 (12) |
C17 | 0.0523 (16) | 0.0673 (18) | 0.0666 (18) | 0.0009 (14) | 0.0087 (14) | 0.0002 (14) |
O18 | 0.0612 (13) | 0.1110 (19) | 0.0760 (14) | 0.0201 (12) | 0.0048 (11) | −0.0046 (12) |
O19 | 0.0692 (14) | 0.0845 (15) | 0.0759 (14) | 0.0167 (11) | 0.0180 (11) | −0.0029 (10) |
C20 | 0.084 (2) | 0.090 (2) | 0.111 (3) | 0.0199 (19) | 0.034 (2) | −0.018 (2) |
C21 | 0.0570 (17) | 0.0631 (18) | 0.0725 (19) | 0.0030 (14) | 0.0095 (14) | −0.0012 (14) |
O22 | 0.0581 (14) | 0.0657 (14) | 0.162 (2) | 0.0134 (11) | 0.0152 (14) | 0.0152 (13) |
O23 | 0.0642 (14) | 0.0687 (14) | 0.1133 (18) | −0.0020 (10) | 0.0297 (12) | 0.0048 (11) |
C24 | 0.098 (3) | 0.067 (2) | 0.102 (3) | −0.0158 (19) | 0.030 (2) | 0.0102 (17) |
N1—C5 | 1.358 (4) | O13—C14 | 1.472 (4) |
N1—C2 | 1.420 (4) | C14—H14A | 0.9600 |
N1—C6 | 1.470 (3) | C14—H14B | 0.9600 |
C2—C3 | 1.366 (4) | C14—H14C | 0.9600 |
C2—C11 | 1.462 (4) | C15—C16 | 1.334 (4) |
C3—C4 | 1.433 (4) | C15—H15 | 0.9300 |
C3—H3 | 0.9300 | C16—C21 | 1.494 (4) |
C4—C5 | 1.394 (4) | C16—C17 | 1.513 (4) |
C4—C15 | 1.451 (4) | C17—O18 | 1.211 (3) |
C5—H5 | 0.9300 | C17—O19 | 1.326 (3) |
C6—C7 | 1.517 (4) | O19—C20 | 1.460 (4) |
C6—H6A | 0.9700 | C20—H20A | 0.9600 |
C6—H6B | 0.9700 | C20—H20B | 0.9600 |
C7—O8 | 1.208 (3) | C20—H20C | 0.9600 |
C7—O9 | 1.338 (3) | C21—O22 | 1.205 (3) |
O9—C10 | 1.455 (4) | C21—O23 | 1.342 (3) |
C10—H10A | 0.9600 | O23—C24 | 1.456 (4) |
C10—H10B | 0.9600 | C24—H24A | 0.9600 |
C10—H10C | 0.9600 | C24—H24B | 0.9600 |
C11—O12 | 1.204 (3) | C24—H24C | 0.9600 |
C11—O13 | 1.340 (3) | ||
C5—N1—C2 | 109.0 (2) | C11—O13—C14 | 114.7 (2) |
C5—N1—C6 | 124.8 (2) | O13—C14—H14A | 109.5 |
C2—N1—C6 | 126.2 (2) | O13—C14—H14B | 109.5 |
C3—C2—N1 | 106.7 (3) | H14A—C14—H14B | 109.5 |
C3—C2—C11 | 131.4 (3) | O13—C14—H14C | 109.5 |
N1—C2—C11 | 121.9 (3) | H14A—C14—H14C | 109.5 |
C2—C3—C4 | 109.2 (2) | H14B—C14—H14C | 109.5 |
C2—C3—H3 | 125.4 | C16—C15—C4 | 129.6 (3) |
C4—C3—H3 | 125.4 | C16—C15—H15 | 115.2 |
C5—C4—C3 | 105.8 (2) | C4—C15—H15 | 115.2 |
C5—C4—C15 | 129.3 (2) | C15—C16—C21 | 119.1 (2) |
C3—C4—C15 | 124.8 (2) | C15—C16—C17 | 123.2 (3) |
N1—C5—C4 | 109.3 (2) | C21—C16—C17 | 117.7 (2) |
N1—C5—H5 | 125.4 | O18—C17—O19 | 124.6 (3) |
C4—C5—H5 | 125.4 | O18—C17—C16 | 124.0 (3) |
N1—C6—C7 | 111.0 (2) | O19—C17—C16 | 111.4 (2) |
N1—C6—H6A | 109.4 | C17—O19—C20 | 115.8 (2) |
C7—C6—H6A | 109.4 | O19—C20—H20A | 109.5 |
N1—C6—H6B | 109.4 | O19—C20—H20B | 109.5 |
C7—C6—H6B | 109.4 | H20A—C20—H20B | 109.5 |
H6A—C6—H6B | 108.0 | O19—C20—H20C | 109.5 |
O8—C7—O9 | 123.9 (3) | H20A—C20—H20C | 109.5 |
O8—C7—C6 | 126.4 (3) | H20B—C20—H20C | 109.5 |
O9—C7—C6 | 109.6 (2) | O22—C21—O23 | 124.1 (3) |
C7—O9—C10 | 116.6 (3) | O22—C21—C16 | 124.6 (3) |
O9—C10—H10A | 109.5 | O23—C21—C16 | 111.1 (2) |
O9—C10—H10B | 109.5 | C21—O23—C24 | 115.2 (2) |
H10A—C10—H10B | 109.5 | O23—C24—H24A | 109.5 |
O9—C10—H10C | 109.5 | O23—C24—H24B | 109.5 |
H10A—C10—H10C | 109.5 | H24A—C24—H24B | 109.5 |
H10B—C10—H10C | 109.5 | O23—C24—H24C | 109.5 |
O12—C11—O13 | 124.1 (3) | H24A—C24—H24C | 109.5 |
O12—C11—C2 | 125.0 (3) | H24B—C24—H24C | 109.5 |
O13—C11—C2 | 110.8 (2) | ||
C5—N1—C2—C3 | 0.0 (3) | C3—C2—C11—O13 | −5.1 (4) |
C6—N1—C2—C3 | −179.4 (3) | N1—C2—C11—O13 | 177.2 (2) |
C5—N1—C2—C11 | 178.3 (2) | O12—C11—O13—C14 | 2.5 (4) |
C6—N1—C2—C11 | −1.2 (4) | C2—C11—O13—C14 | −177.6 (2) |
N1—C2—C3—C4 | −1.1 (3) | C5—C4—C15—C16 | −8.3 (5) |
C11—C2—C3—C4 | −179.1 (3) | C3—C4—C15—C16 | 169.2 (3) |
C2—C3—C4—C5 | 1.7 (3) | C4—C15—C16—C21 | −177.9 (3) |
C2—C3—C4—C15 | −176.2 (2) | C4—C15—C16—C17 | 2.7 (5) |
C2—N1—C5—C4 | 1.1 (3) | C15—C16—C17—O18 | 91.5 (4) |
C6—N1—C5—C4 | −179.5 (2) | C21—C16—C17—O18 | −87.9 (4) |
C3—C4—C5—N1 | −1.7 (3) | C15—C16—C17—O19 | −88.5 (3) |
C15—C4—C5—N1 | 176.2 (3) | C21—C16—C17—O19 | 92.0 (3) |
C5—N1—C6—C7 | −109.3 (3) | O18—C17—O19—C20 | −1.1 (4) |
C2—N1—C6—C7 | 70.1 (3) | C16—C17—O19—C20 | 179.0 (2) |
N1—C6—C7—O8 | 22.4 (4) | C15—C16—C21—O22 | 6.0 (5) |
N1—C6—C7—O9 | −158.4 (2) | C17—C16—C21—O22 | −174.5 (3) |
O8—C7—O9—C10 | −4.6 (4) | C15—C16—C21—O23 | −177.5 (2) |
C6—C7—O9—C10 | 176.2 (3) | C17—C16—C21—O23 | 1.9 (4) |
C3—C2—C11—O12 | 174.9 (3) | O22—C21—O23—C24 | −1.4 (4) |
N1—C2—C11—O12 | −2.9 (5) | C16—C21—O23—C24 | −177.8 (2) |
Experimental details
Crystal data | |
Chemical formula | C15H17NO8 |
Mr | 339.30 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 293 |
a, b, c (Å) | 9.906 (4), 12.528 (5), 13.991 (5) |
β (°) | 105.44 (4) |
V (Å3) | 1673.7 (11) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.11 |
Crystal size (mm) | 0.35 × 0.30 × 0.10 |
Data collection | |
Diffractometer | Syntex P21 diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3064, 2883, 1837 |
Rint | 0.037 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.059, 0.197, 1.00 |
No. of reflections | 2883 |
No. of parameters | 221 |
H-atom treatment | Riding |
Δρmax, Δρmin (e Å−3) | 0.23, −0.18 |
Computer programs: Syntex software (Syntex, 1973), Syntex software, XP21 (Pavelčík, 1987), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976), SHELXL97.
N1—C5 | 1.358 (4) | C4—C5 | 1.394 (4) |
N1—C2 | 1.420 (4) | C4—C15 | 1.451 (4) |
N1—C6 | 1.470 (3) | C15—C16 | 1.334 (4) |
C2—C3 | 1.366 (4) | C16—C21 | 1.494 (4) |
C2—C11 | 1.462 (4) | C16—C17 | 1.513 (4) |
C3—C4 | 1.433 (4) | ||
C5—N1—C2 | 109.0 (2) | C5—C4—C15 | 129.3 (2) |
C5—N1—C6 | 124.8 (2) | C3—C4—C15 | 124.8 (2) |
C2—N1—C6 | 126.2 (2) | N1—C5—C4 | 109.3 (2) |
C3—C2—N1 | 106.7 (3) | C16—C15—C4 | 129.6 (3) |
C3—C2—C11 | 131.4 (3) | C15—C16—C21 | 119.1 (2) |
N1—C2—C11 | 121.9 (3) | C15—C16—C17 | 123.2 (3) |
C2—C3—C4 | 109.2 (2) | C21—C16—C17 | 117.7 (2) |
C5—C4—C3 | 105.8 (2) | ||
C2—N1—C6—C7 | 70.1 (3) | C4—C15—C16—C17 | 2.7 (5) |
N1—C6—C7—O8 | 22.4 (4) | C15—C16—C17—O18 | 91.5 (4) |
N1—C2—C11—O12 | −2.9 (5) | C15—C16—C21—O22 | 6.0 (5) |
C5—C4—C15—C16 | −8.3 (5) |
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Over the last decade, 2-alkoxycarbonyl pyrrole derivatives have attracted considerable interest as they display a broad spectrum of biological activities, the analgesic, morphine agonist, spasmolytic, antipyretic and antiinflammatory properties being some of the most important (Gribble, 1996). Recently, it has been reported that introduction of additional alkoxycarbonyl group(s) to the 4- and/or 1-position of the pyrrole ring has a favourable effect on the spasmolytic activity. Therefore, our strategy was to incorporate extra 2,2-bis(methoxycarbonyl)vinyl and methoxycarbonylmethyl substituents in the 4- and 1-positions of the parent 2-methoxycarbonylpyrrole in order to design novel compounds possessing spasmolytic and possibly other types of biological activity. Moreover, the title molecule, (I), can also be regarded as a push-pull ethylene, a class of compounds exhibiting a variable degree of conjugation across the C═C double bond and also an associated polarization of the molecule, which is responsible for some unique properties of the compounds (e.g. absorption in the near-ultraviolet and visible regions). Thus, the purpose of this X-ray structural analysis was twofold: (1) to determine the spatial distribution of the functional groups as one of the main determinants of the biological activity and (2) to assess the extent of conjugation for the future study of the relationship between the electronic and physicochemical properties of this class of compounds. \sch
The title molecule along with the atom-numbering scheme is illustrated in Fig. 1. As expected, the central pyrrole ring is planar within experimental error [r.m.s. deviation 0.007 (2) Å] and is nearly coplanar with the plane of the ethylenic (C15═C16) bond [dihedral angle 8.8 (1)°]. The twist about the C═C bond, as measured by the angle between the planes through C4,C15,H15 and C16,C17,C21 is 2.3 (1)°. As shown by torsion angles in Table 1, the ester group O22,C21,O23,C24 is approximately coplanar with the C═C double bond while the other, oriented Z to the pyrrolyl ring, is almost perpendicular to the C═C plane, obviously attributable to steric collision with the heterocyclic ring. As to other pyrrole substituents, the methoxycarbonyl group at C2 is also essentially coplanar with the pyrrole plane [dihedral angle 3.8 (1)°] and the methoxycarbonyl group O8,C7,O9,C10 is rotated around the N1—C6 and C6—C7 bonds so that it makes an angle of 72.5 (4)° with the plane of the pyrrole ring.
Although the pyrrole ring and one of the ester groups at C16 are coplanar with the ethylenic plane, there is no conjugation push-pull effect across the C═ C double bond, as shown by the C15═C16 bond distance [1.334 (4) Å], which corresponds to the value of 1.336 (2) Å observed in unpolarized ethylene (Bartell et al., 1965). Similarly, the C16—C17 and C16—C21 bond lengths of 1.513 (4) and 1.494 (4) Å, respectively, are in good agreement with the value 1.487 (5) Å found for a pure C(sp2)—C(sp2) single bond (Shmueli et al., 1973). The absence of polarization across the ethylenic bond explains the colourlessness of the compound. Nevertheless, on the other side of the molecule, some effect of the methoxycarbonyl group (at C2) on the π-electron distribution of the pyrrole ring is visible in the shortening of the C2—C11 bond distance (Table 1) with respect to the value given above for the C(sp2)—C(sp2) single bond, and also in the non-equivalency of the two N—C bonds within the heterocyclic ring. Other bond lengths and angles within the pyrrole ring agree well with those found for unsubstituted pyrrole (Nygaard et al., 1969).