organic compounds
Methyl 2,2-dimethoxy-8-oxo-1-oxaspiro[4.5]deca-6,9-diene-3-carboxylate
aSchool of Chemistry and Chemical Engineering, Southeast University, Southeast University Road 2, Jiangning District, 211189 Nanjing, People's Republic of China
*Correspondence e-mail: lou@seu.edu.cn
In the title molecule, C13H16O6, the cyclohexa-1,4-diene ring adopts a flat boat conformation (r.m.s. deviation from planarity = 0.060 Å) and the five-membered tetrahydrofuran ring adopts an with the carboxyl group-substituted C atom as the flap. The dihedral angle at the spiro junction is 89.1 (1)°. In the crystal, molecules are linked through weak C—H⋯O and van der Waals interactions.
Related literature
For background to bioactive tetronic acid derivatives, see: Fischer et al. (1993); Bayer Aktiengesellschaft (1995).
Experimental
Crystal data
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Refinement
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Data collection: SMART (Bruker, 2000); cell SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.
Supporting information
10.1107/S1600536812011737/qk2030sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536812011737/qk2030Isup2.hkl
Supporting information file. DOI: 10.1107/S1600536812011737/qk2030Isup3.cml
The starting material and all intermediates are known from literature and are obtained by standard procedures. The title compound was synthesized starting with 4-hydroxybenzaldehyde according to Fig. 3. using standard procedures for the intermediates 2 through 5. Then, to a solution of 5 (800 mg, 3.36 mmol) in MeOH (12 ml) was added a solution of PhI(OAc)2 (1.6 g, 4.97 mmol) in CH2Cl2 (7 ml) at room temperature. The mixture was stirred for 30 min. The solvent was removed under reduced pressure and the residue was purified by silica gel δ 2.28 (dd, J =9.2 Hz, 13.6 Hz, 1H), 2.72 (dd, J = 8.0 Hz, 13.6 Hz, 1H), 3.38 (s, 3H), 3.46 (s, 3H), 3.78 (s, 3H), 6.15–6.20 (m, 2H), 6.89–6.92 (m, 1H), 7.07–7.10 (m, 1H). 13C NMR (100 MHz, CDCl3) δ 36.9, 48.4, 49.9, 51.1, 52.4, 75.8, 122.2, 127.6, 148.2, 149.2, 169.5, 185.0.
(EtOAc: PE = 1:3) to afford 6 (648.1 mg, 72% yield). 1H NMR (400 MHz, CDCl3)All H atoms were placed in calculated positions with C—H = 0.93–0.98Å and were included in the final cycle of
in the riding mode with Uiso(H) = 1.2 or 1.5Ueq(C).The chemistry of tetronic acid (tetrahydrofuran-2,4-dione) compounds has received increasing attention in recent years due to their high biological activity as herbicides and insecticides (Fischer et al., 1993). The company Bayer AG has developed three tetronic acid pesticides, spirodiclofen, spiromesifen, and spirotetramat (Bayer Aktiengesellschaft, 1995), which are now in wide use in crop protection. As part of our studies in this area, we describe here the structure of the title compound (Scheme 1).
The title molecule (Fig. 1) contains one six-membered and one five-membered ring connected with a spiro-carbon C4. All bond lengths in this spiro system adopt normal values, e.g. the double bonds C2═C3, C5═C6, and C1═O1 with values of 1.320 (3) Å, 1.322 (3) Å, and 1.219 (2) Å, respectively. The cyclohexadienone unit is slightly bent to a flat boat conformation with atoms C2, C3, C5, C6 being practically coplanar and C1, C4, and O1 by 0.087 (3), 0.0163 (3), and 0.191 (5) Å, respectively, off from the plane of the former atoms. The five-membered tetrahydrofuran ring adopts an with C8 by 0.558 (3) Å out of the least-squares plane through O2, C4, C7, and C9 (their r.m.s. deviation from l.s. plane is 0.017 Å). In the crystal (Fig. 2), the molecules are linked through weak van der Waals and C-H···O interactions.
For background to bioactive tetronic acid derivatives, see: Fischer et al. (1993); Bayer Aktiengesellschaft (1995).
Data collection: SMART (Bruker, 2000); cell
SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C13H16O6 | F(000) = 568 |
Mr = 268.26 | Dx = 1.345 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 2543 reflections |
a = 6.5324 (7) Å | θ = 5.9–49.9° |
b = 11.7519 (12) Å | µ = 0.11 mm−1 |
c = 17.4204 (18) Å | T = 298 K |
β = 97.723 (2)° | Prismatic, colorless |
V = 1325.2 (2) Å3 | 0.31 × 0.26 × 0.21 mm |
Z = 4 |
Bruker SMART CCD diffractometer | 2588 independent reflections |
Radiation source: fine-focus sealed tube | 2140 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.020 |
φ and ω scans | θmax = 26.0°, θmin = 2.1° |
Absorption correction: multi-scan (SADABS; Bruker, 2000) | h = −7→8 |
Tmin = 0.958, Tmax = 0.978 | k = −14→14 |
7015 measured reflections | l = −13→21 |
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)] = 0.048 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.140 | H-atom parameters constrained |
S = 1.05 | w = 1/[σ2(Fo2) + (0.0751P)2 + 0.297P] where P = (Fo2 + 2Fc2)/3 |
2588 reflections | (Δ/σ)max < 0.001 |
175 parameters | Δρmax = 0.29 e Å−3 |
0 restraints | Δρmin = −0.22 e Å−3 |
C13H16O6 | V = 1325.2 (2) Å3 |
Mr = 268.26 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 6.5324 (7) Å | µ = 0.11 mm−1 |
b = 11.7519 (12) Å | T = 298 K |
c = 17.4204 (18) Å | 0.31 × 0.26 × 0.21 mm |
β = 97.723 (2)° |
Bruker SMART CCD diffractometer | 2588 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2000) | 2140 reflections with I > 2σ(I) |
Tmin = 0.958, Tmax = 0.978 | Rint = 0.020 |
7015 measured reflections |
R[F2 > 2σ(F2)] = 0.048 | 0 restraints |
wR(F2) = 0.140 | H-atom parameters constrained |
S = 1.05 | Δρmax = 0.29 e Å−3 |
2588 reflections | Δρmin = −0.22 e Å−3 |
175 parameters |
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 | −0.2524 (3) | 0.60788 (16) | −0.03288 (8) | 0.0876 (5) | |
O2 | 0.0228 (2) | 0.64745 (11) | 0.26381 (7) | 0.0560 (4) | |
O3 | 0.5107 (3) | 0.39189 (16) | 0.31643 (8) | 0.0826 (5) | |
O4 | 0.34081 (19) | 0.39820 (12) | 0.41846 (7) | 0.0571 (4) | |
O5 | 0.08806 (19) | 0.62430 (12) | 0.39416 (7) | 0.0567 (4) | |
O6 | 0.35585 (19) | 0.64129 (11) | 0.32927 (7) | 0.0546 (4) | |
C1 | −0.1786 (3) | 0.60713 (17) | 0.03521 (11) | 0.0601 (5) | |
C2 | 0.0197 (3) | 0.66200 (19) | 0.06170 (12) | 0.0665 (6) | |
H2 | 0.0846 | 0.7040 | 0.0267 | 0.080* | |
C3 | 0.1080 (3) | 0.65306 (19) | 0.13416 (12) | 0.0639 (6) | |
H3 | 0.2302 | 0.6927 | 0.1491 | 0.077* | |
C4 | 0.0216 (3) | 0.58253 (16) | 0.19334 (10) | 0.0510 (4) | |
C5 | −0.1957 (3) | 0.54671 (16) | 0.16723 (11) | 0.0553 (5) | |
H5 | −0.2722 | 0.5170 | 0.2039 | 0.066* | |
C6 | −0.2852 (3) | 0.55504 (17) | 0.09477 (12) | 0.0601 (5) | |
H6 | −0.4186 | 0.5272 | 0.0815 | 0.072* | |
C7 | 0.1620 (3) | 0.47845 (17) | 0.21615 (10) | 0.0584 (5) | |
H7A | 0.1032 | 0.4096 | 0.1916 | 0.070* | |
H7B | 0.2989 | 0.4899 | 0.2018 | 0.070* | |
C8 | 0.1695 (3) | 0.47217 (14) | 0.30329 (9) | 0.0460 (4) | |
H8 | 0.0463 | 0.4327 | 0.3160 | 0.055* | |
C9 | 0.1579 (2) | 0.59822 (14) | 0.32513 (9) | 0.0440 (4) | |
C10 | 0.3594 (3) | 0.41569 (15) | 0.34472 (10) | 0.0490 (4) | |
C11 | 0.5178 (3) | 0.35071 (19) | 0.46569 (12) | 0.0659 (6) | |
H11A | 0.5372 | 0.2734 | 0.4503 | 0.099* | |
H11B | 0.4961 | 0.3525 | 0.5191 | 0.099* | |
H11C | 0.6383 | 0.3945 | 0.4592 | 0.099* | |
C12 | −0.1168 (4) | 0.5942 (3) | 0.40212 (17) | 0.0983 (10) | |
H12A | −0.2091 | 0.6268 | 0.3604 | 0.147* | |
H12B | −0.1506 | 0.6224 | 0.4506 | 0.147* | |
H12C | −0.1304 | 0.5129 | 0.4008 | 0.147* | |
C13 | 0.3702 (4) | 0.76269 (19) | 0.33775 (14) | 0.0778 (7) | |
H13A | 0.3063 | 0.7985 | 0.2911 | 0.117* | |
H13B | 0.5130 | 0.7846 | 0.3475 | 0.117* | |
H13C | 0.3011 | 0.7861 | 0.3804 | 0.117* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0973 (12) | 0.1070 (13) | 0.0497 (9) | −0.0063 (10) | −0.0219 (8) | 0.0074 (8) |
O2 | 0.0571 (7) | 0.0555 (7) | 0.0502 (7) | 0.0126 (6) | −0.0116 (6) | −0.0035 (5) |
O3 | 0.0771 (10) | 0.1179 (14) | 0.0537 (9) | 0.0494 (10) | 0.0115 (7) | 0.0034 (8) |
O4 | 0.0570 (8) | 0.0695 (9) | 0.0441 (7) | 0.0098 (6) | 0.0041 (6) | 0.0112 (6) |
O5 | 0.0510 (7) | 0.0703 (8) | 0.0485 (7) | 0.0051 (6) | 0.0056 (6) | −0.0117 (6) |
O6 | 0.0456 (7) | 0.0566 (8) | 0.0596 (8) | −0.0074 (5) | −0.0004 (6) | 0.0070 (6) |
C1 | 0.0633 (12) | 0.0596 (11) | 0.0518 (11) | 0.0056 (9) | −0.0125 (9) | 0.0026 (9) |
C2 | 0.0652 (12) | 0.0766 (14) | 0.0554 (11) | −0.0081 (10) | −0.0006 (9) | 0.0161 (10) |
C3 | 0.0510 (11) | 0.0787 (14) | 0.0582 (12) | −0.0127 (9) | −0.0067 (9) | 0.0101 (10) |
C4 | 0.0487 (10) | 0.0578 (11) | 0.0431 (9) | 0.0014 (8) | −0.0061 (7) | 0.0020 (7) |
C5 | 0.0511 (10) | 0.0576 (11) | 0.0547 (11) | −0.0061 (8) | −0.0021 (8) | 0.0050 (8) |
C6 | 0.0509 (10) | 0.0617 (11) | 0.0622 (12) | −0.0066 (9) | −0.0130 (9) | 0.0016 (9) |
C7 | 0.0630 (11) | 0.0667 (12) | 0.0420 (9) | 0.0149 (9) | −0.0059 (8) | −0.0057 (8) |
C8 | 0.0452 (9) | 0.0484 (10) | 0.0430 (9) | 0.0024 (7) | 0.0012 (7) | −0.0013 (7) |
C9 | 0.0387 (8) | 0.0505 (9) | 0.0413 (9) | 0.0014 (7) | −0.0001 (7) | −0.0002 (7) |
C10 | 0.0560 (10) | 0.0491 (9) | 0.0412 (9) | 0.0090 (8) | 0.0039 (8) | −0.0024 (7) |
C11 | 0.0665 (13) | 0.0759 (14) | 0.0525 (11) | 0.0154 (10) | −0.0029 (9) | 0.0168 (10) |
C12 | 0.0590 (14) | 0.152 (3) | 0.0895 (18) | −0.0069 (15) | 0.0299 (13) | −0.0282 (17) |
C13 | 0.0921 (16) | 0.0582 (12) | 0.0756 (14) | −0.0239 (11) | −0.0158 (12) | 0.0146 (11) |
O1—C1 | 1.219 (2) | C5—C6 | 1.321 (3) |
O2—C9 | 1.4148 (19) | C5—H5 | 0.9300 |
O2—C4 | 1.444 (2) | C6—H6 | 0.9300 |
O3—C10 | 1.195 (2) | C7—C8 | 1.514 (2) |
O4—C10 | 1.323 (2) | C7—H7A | 0.9700 |
O4—C11 | 1.439 (2) | C7—H7B | 0.9700 |
O5—C9 | 1.377 (2) | C8—C10 | 1.503 (2) |
O5—C12 | 1.409 (3) | C8—C9 | 1.534 (2) |
O6—C9 | 1.381 (2) | C8—H8 | 0.9800 |
O6—C13 | 1.436 (3) | C11—H11A | 0.9600 |
C1—C6 | 1.460 (3) | C11—H11B | 0.9600 |
C1—C2 | 1.465 (3) | C11—H11C | 0.9600 |
C2—C3 | 1.320 (3) | C12—H12A | 0.9600 |
C2—H2 | 0.9300 | C12—H12B | 0.9600 |
C3—C4 | 1.492 (3) | C12—H12C | 0.9600 |
C3—H3 | 0.9300 | C13—H13A | 0.9600 |
C4—C5 | 1.492 (2) | C13—H13B | 0.9600 |
C4—C7 | 1.549 (3) | C13—H13C | 0.9600 |
C9—O2—C4 | 110.94 (13) | C10—C8—C9 | 111.85 (14) |
C10—O4—C11 | 116.36 (15) | C7—C8—C9 | 101.87 (14) |
C9—O5—C12 | 117.44 (16) | C10—C8—H8 | 109.4 |
C9—O6—C13 | 114.67 (16) | C7—C8—H8 | 109.4 |
O1—C1—C6 | 122.06 (19) | C9—C8—H8 | 109.4 |
O1—C1—C2 | 121.4 (2) | O5—C9—O6 | 106.90 (13) |
C6—C1—C2 | 116.54 (16) | O5—C9—O2 | 108.78 (13) |
C3—C2—C1 | 121.39 (19) | O6—C9—O2 | 111.98 (14) |
C3—C2—H2 | 119.3 | O5—C9—C8 | 117.70 (15) |
C1—C2—H2 | 119.3 | O6—C9—C8 | 106.86 (14) |
C2—C3—C4 | 123.21 (18) | O2—C9—C8 | 104.72 (13) |
C2—C3—H3 | 118.4 | O3—C10—O4 | 123.58 (16) |
C4—C3—H3 | 118.4 | O3—C10—C8 | 125.45 (16) |
O2—C4—C5 | 107.74 (15) | O4—C10—C8 | 110.94 (15) |
O2—C4—C3 | 109.54 (16) | O4—C11—H11A | 109.5 |
C5—C4—C3 | 112.28 (15) | O4—C11—H11B | 109.5 |
O2—C4—C7 | 105.29 (13) | H11A—C11—H11B | 109.5 |
C5—C4—C7 | 111.23 (16) | O4—C11—H11C | 109.5 |
C3—C4—C7 | 110.48 (16) | H11A—C11—H11C | 109.5 |
C6—C5—C4 | 123.44 (19) | H11B—C11—H11C | 109.5 |
C6—C5—H5 | 118.3 | O5—C12—H12A | 109.5 |
C4—C5—H5 | 118.3 | O5—C12—H12B | 109.5 |
C5—C6—C1 | 121.19 (18) | H12A—C12—H12B | 109.5 |
C5—C6—H6 | 119.4 | O5—C12—H12C | 109.5 |
C1—C6—H6 | 119.4 | H12A—C12—H12C | 109.5 |
C8—C7—C4 | 103.53 (14) | H12B—C12—H12C | 109.5 |
C8—C7—H7A | 111.1 | O6—C13—H13A | 109.5 |
C4—C7—H7A | 111.1 | O6—C13—H13B | 109.5 |
C8—C7—H7B | 111.1 | H13A—C13—H13B | 109.5 |
C4—C7—H7B | 111.1 | O6—C13—H13C | 109.5 |
H7A—C7—H7B | 109.0 | H13A—C13—H13C | 109.5 |
C10—C8—C7 | 114.59 (15) | H13B—C13—H13C | 109.5 |
O1—C1—C2—C3 | −174.2 (2) | C12—O5—C9—O2 | 55.5 (2) |
C6—C1—C2—C3 | 7.7 (3) | C12—O5—C9—C8 | −63.3 (2) |
C1—C2—C3—C4 | 3.4 (4) | C13—O6—C9—O5 | −62.06 (19) |
C9—O2—C4—C5 | 122.48 (15) | C13—O6—C9—O2 | 57.0 (2) |
C9—O2—C4—C3 | −115.12 (16) | C13—O6—C9—C8 | 171.10 (15) |
C9—O2—C4—C7 | 3.68 (19) | C4—O2—C9—O5 | −151.91 (14) |
C2—C3—C4—O2 | −133.2 (2) | C4—O2—C9—O6 | 90.16 (17) |
C2—C3—C4—C5 | −13.5 (3) | C4—O2—C9—C8 | −25.26 (18) |
C2—C3—C4—C7 | 111.3 (2) | C10—C8—C9—O5 | −79.84 (19) |
O2—C4—C5—C6 | 134.4 (2) | C7—C8—C9—O5 | 157.31 (15) |
C3—C4—C5—C6 | 13.7 (3) | C10—C8—C9—O6 | 40.30 (19) |
C7—C4—C5—C6 | −110.7 (2) | C7—C8—C9—O6 | −82.55 (16) |
C4—C5—C6—C1 | −3.7 (3) | C10—C8—C9—O2 | 159.24 (14) |
O1—C1—C6—C5 | 174.4 (2) | C7—C8—C9—O2 | 36.39 (17) |
C2—C1—C6—C5 | −7.5 (3) | C11—O4—C10—O3 | 1.8 (3) |
O2—C4—C7—C8 | 19.56 (19) | C11—O4—C10—C8 | −176.39 (16) |
C5—C4—C7—C8 | −96.87 (18) | C7—C8—C10—O3 | 11.3 (3) |
C3—C4—C7—C8 | 137.73 (16) | C9—C8—C10—O3 | −104.0 (2) |
C4—C7—C8—C10 | −154.35 (15) | C7—C8—C10—O4 | −170.64 (16) |
C4—C7—C8—C9 | −33.39 (18) | C9—C8—C10—O4 | 74.07 (19) |
C12—O5—C9—O6 | 176.6 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
C13—H13A···O3i | 0.96 | 2.60 | 3.269 (3) | 127 |
Symmetry code: (i) −x+1, y+1/2, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C13H16O6 |
Mr | 268.26 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 298 |
a, b, c (Å) | 6.5324 (7), 11.7519 (12), 17.4204 (18) |
β (°) | 97.723 (2) |
V (Å3) | 1325.2 (2) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.11 |
Crystal size (mm) | 0.31 × 0.26 × 0.21 |
Data collection | |
Diffractometer | Bruker SMART CCD |
Absorption correction | Multi-scan (SADABS; Bruker, 2000) |
Tmin, Tmax | 0.958, 0.978 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7015, 2588, 2140 |
Rint | 0.020 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.048, 0.140, 1.05 |
No. of reflections | 2588 |
No. of parameters | 175 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.29, −0.22 |
Computer programs: SMART (Bruker, 2000), SAINT (Bruker, 2000), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
C13—H13A···O3i | 0.96 | 2.60 | 3.269 (3) | 127 |
Symmetry code: (i) −x+1, y+1/2, −z+1/2. |
Acknowledgements
This project was sponsored by the National Science Foundation of Jiangsu Province (No. BK2009262) and the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry.
References
Bayer Aktiengesellschaft (1995). WO Patent No. 9 504 719A1. Google Scholar
Bruker (2000). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Fischer, R. M., Bretschneider, T. S. & Kruger, B.-W. (1993). US Patent No. 5 262 383. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
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The chemistry of tetronic acid (tetrahydrofuran-2,4-dione) compounds has received increasing attention in recent years due to their high biological activity as herbicides and insecticides (Fischer et al., 1993). The company Bayer AG has developed three tetronic acid pesticides, spirodiclofen, spiromesifen, and spirotetramat (Bayer Aktiengesellschaft, 1995), which are now in wide use in crop protection. As part of our studies in this area, we describe here the structure of the title compound (Scheme 1).
The title molecule (Fig. 1) contains one six-membered and one five-membered ring connected with a spiro-carbon C4. All bond lengths in this spiro system adopt normal values, e.g. the double bonds C2═C3, C5═C6, and C1═O1 with values of 1.320 (3) Å, 1.322 (3) Å, and 1.219 (2) Å, respectively. The cyclohexadienone unit is slightly bent to a flat boat conformation with atoms C2, C3, C5, C6 being practically coplanar and C1, C4, and O1 by 0.087 (3), 0.0163 (3), and 0.191 (5) Å, respectively, off from the plane of the former atoms. The five-membered tetrahydrofuran ring adopts an envelope conformation with C8 by 0.558 (3) Å out of the least-squares plane through O2, C4, C7, and C9 (their r.m.s. deviation from l.s. plane is 0.017 Å). In the crystal (Fig. 2), the molecules are linked through weak van der Waals and C-H···O interactions.