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The mol­ecule of the title compound, methyl 1-formyl-6-oxa-6H-indene-4-carboxyl­ate, C11H8O4, is planar. There are weak C-H...O intramolecular interactions and an intermolecular hydrogen bond in the structure, and these influence the crystal packing.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101014317/ta1345sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270101014317/ta1345Isup2.hkl
Contains datablock I

CCDC reference: 175113

Comment top

Plants of the Cerbera species are distributed widely in the coastal areas of Southeast Asia and countries surrounding the Indian Ocean. Several research groups have previously isolated various groups of compounds from Cerbera odollam and Cerbera manghas, such as cardenolide glycosides, lignans and normonoterpenoids (Abe et al., 1977, 1988a,b, 1989; Mahran et al., 1972; Malathy & Krishnamoorthy, 1978; Li et al., 1981; Rao et al., 1973, 1974; Yamauchi, 1987). Previously, cerbinal, a yellow compound having an iridoid skeleton, was reported to be isolated from the bark of Cerbera manghas (Abe et al., 1977) and was identified by spectroscopic methods but there is no information about its bioactivity. Recently, our group isolated cerbinal from the bark of Cerbera odollam. Preliminary testing against mycobacterium tuberculosis and breast-cancer cells exhibited moderate bioactivity.

The NMR spectrum and a resonance-theory prediction for the title compound, (I), suggested that the planarity of the molecule would allow electron delocalization from the ring O atom towards the five-membered ring. The planarity of the molecule was confirmed by the present structure determination. The electron delocalization was also confirmed by a theoretical calculation of the charge distributions using a PC version of MOPAC97, with an AM1 set of parameters. Full optimization of the ground-state gas-phase structure gives the results presented in Fig. 1. The dipole is directed from C4 towards, but slightly below, C5. This molecule might be useful as a simple model for stereoselectivity studies and as a starting material in other syntheses.

The title compound (Fig. 2) has a planar aromatic structure, with a highly conjugated π system. The bond lengths and angles show normal values (Table 1) (Allen et al., 1987); C1—C2 and C3—C4 show double-bond character. The fused five-membered and pyran rings are planar, with the C2 atom deviating by a maximum of 0.007 (3) Å. The mean plane through the fused five-membered ring forms a dihedral angle of 0.08 (16)° with the mean plane of the pyran ring. The carbomethoxyl and formyl groups are coplanar with their attached rings [C4—C10—O4—C11 = 179.1 (3)° and C7—C8—C9—O1 = 179.5 (3)°]. Two weak intramolecular C—H···O interactions form O4—C10—C4—C3—H3A and O2—C10—C4—C5—C6—H6A closed rings. The O atoms of the carbomethoxyl group are involved in these weak intramolecular interactions; C3—H3A···O4 [H3A···O4 = 2.3284 Å and C3—H3A···O4 = 103°] and C6—H6A···O2 [H6A···O2 = 2.5699 Å and C6—H6A···O2 = 109°], whereas the O atom of formyl group is involved in an intermolecular hydrogen bond (Table 2). In additon, two intermolecular ππ interactions between the centroids of five- and six-membered ring, i.e. Cg1 and Cg2, respectively, were also observed; Cg1···Cg2ii = 3.571 Å and Cg1···Cg2iii = 3.575 Å [symmetry codes: (ii) -1 - x, 1/2 + y, 3/2 - z; (iii) -x, 1/2 + y, 3/2 - z]. These ππ interactions are analogous to charge-transfer interactions in complexes. The intermolecular C—H···O interactions interconnect the molecules into infinite molecular ribbons along the c axis and these ribbons are stacked along the a axis (Fig. 3). All these interactions, as well as van der Waals interactions, stabilize the molecular and acentric packing structure in the crystal.

Related literature top

For related literature, see: Abe et al. (1977, 1988a, 1988b, 1989); Allen et al. (1987); Li et al. (1981); Mahran et al. (1972); Malathy & Krishnamoorthy (1978); Rao (1973); Rao et al. (1974); Yamauchi et al. (1987).

Experimental top

The air-dried bark of Cerbera odollam (1.50 kg) was ground and extracted by soaking in hexane (25 l) for 5 d at room temperature. The mixture was filtered and concentrated under reduced pressure to give the crude extracts. Upon concentration under reduced pressure, the hexane extract yielded precipitates which were filtered out and recrystallized from CHCl3 to yield yellow needle-shaped crystals of compound (I) (m.p. 449–451 K).

Refinement top

H atoms were refined as riding with C—H distances of 0.93 and 0.96 Å.

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 1990).

Figures top
[Figure 1] Fig. 1. The MOPAC97-calculated charge distribution on the title compound. The direction of the calculated dipole moment (1.91 D) is indicated by the arrow.
[Figure 2] Fig. 2. The structure of the title compound showing 50% probability displacement ellipsoids and the atom-numbering scheme.
[Figure 3] Fig. 3. Packing diagram of the title compound viewed down the a axis. The hydrogen bonds are represented by dashed lines.
Methyl 1-formyl-6-oxa-6H-indene-4-carboxylate top
Crystal data top
C11H8O4Dx = 1.479 Mg m3
Mr = 204.17Melting point: 449-451 K K
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
a = 6.8622 (2) ÅCell parameters from 3144 reflections
b = 10.8244 (1) Åθ = 2.5–28.3°
c = 12.3446 (3) ŵ = 0.11 mm1
V = 916.95 (4) Å3T = 293 K
Z = 4Needle, yellow
F(000) = 4240.46 × 0.16 × 0.14 mm
Data collection top
Siemens SMART CCD area-detector
diffractometer
900 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.083
Graphite monochromatorθmax = 28.3°, θmin = 2.5°
Detector resolution: 8.33 pixels mm-1h = 98
ω scansk = 1314
6418 measured reflectionsl = 1611
1323 independent reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.056H-atom parameters constrained
wR(F2) = 0.145 w = 1/[σ2(Fo2) + (0.0799P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.01(Δ/σ)max = 0.036
1323 reflectionsΔρmax = 0.35 e Å3
138 parametersΔρmin = 0.45 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.015 (5)
Crystal data top
C11H8O4V = 916.95 (4) Å3
Mr = 204.17Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 6.8622 (2) ŵ = 0.11 mm1
b = 10.8244 (1) ÅT = 293 K
c = 12.3446 (3) Å0.46 × 0.16 × 0.14 mm
Data collection top
Siemens SMART CCD area-detector
diffractometer
900 reflections with I > 2σ(I)
6418 measured reflectionsRint = 0.083
1323 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0560 restraints
wR(F2) = 0.145H-atom parameters constrained
S = 1.01Δρmax = 0.35 e Å3
1323 reflectionsΔρmin = 0.45 e Å3
138 parameters
Special details top

Experimental. Crystal decay was monitored by SAINT (Siemens, 1996) and was found to be negligible.

The data collection covered over a hemisphere of reciprocal space by a combination of three sets of exposures; each set had a different ϕ angle (0.88 and 180°) for the crystal and each exposure of 30 s covered 0.3° in ω. The crystal-to-detector distance was 4.023 cm and the detector swing angle was -35°. Coverage of the unit set is 99.5% complete.

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. The structure was solved by direct methods and refined by full-matrix least-squares techniques. After checking their presence in the difference map, all H-atoms were geometrically fixed and allowed to ride on their attached atoms with Uiso = 1.2Ueq for the attached atoms and Uiso = 1.5Ueq for methyl H-atoms. The methyl H-atoms were refined as rigid rotators.

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
O10.1363 (5)0.3189 (2)0.16333 (19)0.0618 (7)
O20.1100 (5)0.12325 (19)0.72795 (17)0.0553 (7)
O30.1279 (4)0.47706 (16)0.49857 (15)0.0410 (6)
O40.1314 (4)0.3151 (2)0.79461 (16)0.0433 (6)
C10.1279 (5)0.2860 (3)0.4065 (2)0.0287 (6)
C20.1313 (6)0.4101 (3)0.4055 (2)0.0366 (7)
H2A0.13610.45130.33940.044*
C30.1239 (6)0.4169 (3)0.5954 (2)0.0356 (7)
H3A0.12180.46410.65830.043*
C40.1229 (5)0.2919 (2)0.6052 (2)0.0276 (6)
C50.1243 (5)0.2191 (2)0.5093 (2)0.0275 (6)
C60.1225 (5)0.0940 (3)0.4859 (2)0.0360 (7)
H6A0.11930.03010.53620.043*
C70.1263 (6)0.0807 (3)0.3717 (2)0.0398 (7)
H7A0.12660.00540.33540.048*
C80.1296 (5)0.1955 (3)0.3213 (2)0.0337 (7)
C90.1345 (6)0.2176 (3)0.2059 (3)0.0445 (8)
H9A0.13650.14890.16060.053*
C100.1214 (5)0.2336 (3)0.7136 (2)0.0339 (6)
C110.1271 (7)0.2634 (3)0.9036 (2)0.0490 (9)
H11A0.13520.32910.95570.074*
H11B0.23550.20840.91300.074*
H11C0.00760.21880.91390.074*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0816 (18)0.0745 (16)0.0293 (12)0.004 (2)0.0014 (14)0.0078 (12)
O20.0955 (19)0.0390 (12)0.0316 (12)0.0035 (16)0.0027 (17)0.0100 (10)
O30.0637 (14)0.0296 (9)0.0298 (11)0.0017 (12)0.0017 (14)0.0028 (9)
O40.0647 (13)0.0451 (11)0.0201 (10)0.0038 (15)0.0014 (12)0.0009 (9)
C10.0267 (13)0.0351 (13)0.0242 (13)0.0013 (18)0.0014 (14)0.0001 (12)
C20.0476 (16)0.0380 (15)0.0242 (14)0.000 (2)0.0031 (17)0.0060 (12)
C30.0500 (16)0.0321 (14)0.0246 (14)0.004 (2)0.0007 (18)0.0012 (12)
C40.0288 (13)0.0312 (13)0.0227 (13)0.0011 (16)0.0002 (15)0.0012 (11)
C50.0235 (12)0.0333 (13)0.0256 (13)0.0040 (17)0.0010 (15)0.0000 (13)
C60.0415 (15)0.0311 (13)0.0354 (16)0.0019 (17)0.0005 (19)0.0024 (13)
C70.0441 (16)0.0403 (16)0.0349 (16)0.0051 (19)0.0014 (19)0.0118 (13)
C80.0327 (14)0.0436 (16)0.0248 (13)0.0013 (19)0.0015 (15)0.0036 (12)
C90.0468 (18)0.0605 (19)0.0261 (15)0.001 (2)0.0032 (18)0.0062 (16)
C100.0360 (15)0.0414 (16)0.0243 (13)0.0023 (18)0.0012 (18)0.0037 (12)
C110.064 (2)0.063 (2)0.0195 (14)0.004 (2)0.0014 (18)0.0049 (13)
Geometric parameters (Å, º) top
O1—C91.217 (4)C4—C51.423 (4)
O2—C101.210 (3)C4—C101.479 (4)
O3—C21.359 (3)C5—C61.384 (4)
O3—C31.361 (3)C6—C71.417 (4)
O4—C101.336 (4)C6—H6A0.9300
O4—C111.457 (4)C7—C81.390 (4)
C1—C21.344 (4)C7—H7A0.9300
C1—C81.438 (4)C8—C91.445 (4)
C1—C51.461 (4)C9—H9A0.9300
C2—H2A0.9300C11—H11A0.9600
C3—C41.359 (4)C11—H11B0.9600
C3—H3A0.9300C11—H11C0.9600
C2—O3—C3119.2 (2)C7—C6—H6A126.1
C10—O4—C11115.9 (2)C8—C7—C6110.8 (3)
C2—C1—C8132.4 (3)C8—C7—H7A124.6
C2—C1—C5120.3 (3)C6—C7—H7A124.6
C8—C1—C5107.3 (2)C7—C8—C1106.3 (2)
C1—C2—O3121.6 (2)C7—C8—C9126.1 (3)
C1—C2—H2A119.2C1—C8—C9127.6 (3)
O3—C2—H2A119.2O1—C9—C8125.1 (3)
C4—C3—O3123.7 (3)O1—C9—H9A117.5
C4—C3—H3A118.1C8—C9—H9A117.5
O3—C3—H3A118.1O2—C10—O4123.1 (3)
C3—C4—C5118.5 (2)O2—C10—C4123.7 (3)
C3—C4—C10120.4 (2)O4—C10—C4113.2 (2)
C5—C4—C10121.1 (2)O4—C11—H11A109.5
C6—C5—C4135.6 (3)O4—C11—H11B109.5
C6—C5—C1107.7 (3)H11A—C11—H11B109.5
C4—C5—C1116.7 (2)O4—C11—H11C109.5
C5—C6—C7107.8 (3)H11A—C11—H11C109.5
C5—C6—H6A126.1H11B—C11—H11C109.5
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C11—H11A···O1i0.962.573.262 (3)130
Symmetry code: (i) x, y, z+1.

Experimental details

Crystal data
Chemical formulaC11H8O4
Mr204.17
Crystal system, space groupOrthorhombic, P212121
Temperature (K)293
a, b, c (Å)6.8622 (2), 10.8244 (1), 12.3446 (3)
V3)916.95 (4)
Z4
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.46 × 0.16 × 0.14
Data collection
DiffractometerSiemens SMART CCD area-detector
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
6418, 1323, 900
Rint0.083
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.056, 0.145, 1.01
No. of reflections1323
No. of parameters138
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.35, 0.45

Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1996), SAINT, SHELXTL (Sheldrick, 1997), SHELXTL and PLATON (Spek, 1990).

Selected geometric parameters (Å, º) top
O1—C91.217 (4)O4—C101.336 (4)
O2—C101.210 (3)O4—C111.457 (4)
O3—C21.359 (3)C1—C21.344 (4)
O3—C31.361 (3)C3—C41.359 (4)
C2—O3—C3119.2 (2)O1—C9—C8125.1 (3)
C10—O4—C11115.9 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C11—H11A···O1i0.962.56583.262 (3)130
Symmetry code: (i) x, y, z+1.
 

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