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The crystal structure of the γ-lactone of racemic 7-oxabi­cyclo­[2.2.1]­heptane-5-exo-iodo-6-endo-hydroxy-2-endo-carboxyl­ic acid has confirmed the position of the lactone bridge as 2–6 and the exo-iodo substituent configuration as previously proposed from chemical and 13C NMR evidence. The iodo substituent is also involved in a short non-bonding intermolecular interaction [I...O 3.289 (5) Å] with the non-bridging lactone oxy­gen giving polymeric chains which link weakly hydrogen-bonded (C—H...O) centrosymmetric dimer units.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801012661/cv6048sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801012661/cv6048Isup2.hkl
Contains datablock I

CCDC reference: 170939

Key indicators

  • Single-crystal X-ray study
  • T = 295 K
  • Mean [sigma](C-C) = 0.007 Å
  • R factor = 0.029
  • wR factor = 0.077
  • Data-to-parameter ratio = 17.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry General Notes
ABSTM_02 When printed, the submitted absorption T values will be replaced by the scaled T values. Since the ratio of scaled T's is identical to the ratio of reported T values, the scaling does not imply a change to the absorption corrections used in the study. Ratio of Tmax expected/reported 0.845 Tmax scaled 0.366 Tmin scaled 0.320 REFLT_03 From the CIF: _diffrn_reflns_theta_max 27.52 From the CIF: _reflns_number_total 1787 From the CIF: _diffrn_reflns_limit_ max hkl 7. 18. 11. From the CIF: _diffrn_reflns_limit_ min hkl 0. 0. -11. TEST1: Expected hkl limits for theta max Calculated maximum hkl 7. 20. 11. Calculated minimum hkl -7. -20. -11. ALERT: Expected hkl max differ from CIF values

Comment top

The γ-lactone of racemic 7-oxabicyclo[2.2.1]heptane-5-exo-iodo-6-endo-hydroxy-2-endo-carboxylic acid was first reported by van Tamelen & Shamma (1954). A modification of the standard Diels–Alder procedure for the synthesis of the 7-oxabicyclo[2.2.1]heptenes using furan with ethyl acrylate rather than maleic anhydride (Kunstmann et al., 1962) gave rise to a series of 2-substituted derivatives (both exo- and endo-isomers) and the title compound, (I), was prepared by these authors from the 2-endo isomer by treatment with iodine/potassium iodide. Later procedures (Kotsuki et al., 1984) employing furan with methyl acrylate in the presence of BF3—OEt catalyst gave high endo-isomer selectivity (ca 75%). The analogous optically active (+)-5-bromo compound has also been resolved and its crystal structure determined (Ogawa et al., 1985).

The crystal structure of the iodo lactone (I) prepared from the alkene synthesized by the method of Kotsuki et al. (1984) has confirmed the exo-configuration of the 5-iodo substituent, as well as the siting of the 2–6 lactone bridge (Fig. 1). The torsion angles C3—-C4–C5—I5 and C1—C2—C21—O21 are -172.0 (3) and -159.1 (5)°, respectively. The relatively inflexible oxabicyclo cage together with its associated lactone bridge is not as common structurally as the corresponding norbornane cage lactone structures (Moriarty et el., 1972; Singh et al., 1974) or the more comparable exo-5-iodo-bicyclo[2.2.2]octane cage lactone structure (Carman et al., 1982). However, the molecular cage in (I) is similar to both these cage structural units and more so to the analogous optically active bromo compound, (+)-7-oxabicyclo[2.2.1]heptane-5-exo-bromo-6-endo-hydroxy-2-endo-carboxylic acid γ-lactone (Ogawa et al., 1985) (comparative torsion angles: -174.5 and -161.7°).

In the packing of the compound in the unit cell, although no formal hydrogen bonds may exist, weak C5—H5····O21i(lactone) interactions [C···O 3.350 (6) Å; symmetry code: (i) -x, -y, 2 - z] join the molecules into centrosymmetric dimers. These are then linked across a b-face diagonal by relatively short intermolecular associations between the iodo substituent and the non-bridging lactone oxygen [I5···O21ii 3.289 (5) Å; symmetry code: (ii) -1 + x, y, -1 + z].

Experimental top

The title compound was synthesized using a variation of the method of Kuntsmann et al. (1962) by the room-temperature reaction of the unsaturated carboxylic acid, racemic 7-oxabicyclo[2.2.1]hept-5-ene-2-endo-carboxylic acid with iodine/potassium iodide for 4 h (72% yield). The acid was prepared from the methyl ester by hydrolysis with 10% aqueous NaOH (room temperature, 1 d). This ester precursor was synthesized using the method of Kotsuki et al. (1984) by a Diels–Alder addition reaction of methyl acrylate with furan in the presence of BF3·OEt2 catalyst (253 K, then 277 K for 10 h). After extraction of the final iodolactone into chloroform, data crystals were obtained by recrystallization from acetone. Spectroscopic data, FT—IR (cm-1): 2996.3 (C—H stretch, aliphatic), 1786.2 (CO stretch), 1190.0 (C—O stretch, lactone), 1022.7 (C—O stretch, ether bridge); 1H NMR (CDCl3, p.p.m.): δ 2.00–2.30 (2H, m, C-3 methylene), 2.65–2.85 (1H, m, H-2), 3.29 (1H, s, H-5), 4.77 (1H, m., H-4), 5.08 (1H, d, H-6, J1,6 = 5 Hz), 5.34 (1H, t, H-1, J1,2 = 5 Hz); 13C NMR (CDCl3, p.p.m.): δ 25.02 (C-5), 36.13 (C-3), 38.06 (C-2), 81.87 (C-6), 84.21 (C-4), 87.52 (C-1), 175.76 (CO); 13C NMR (DEPT, p.p.m.): δ 25.02 (CH), 36.13 (CH2), 38.06 (CH), 81.87 (CH), 84.21 (CH), 87.52 (CH).

Refinement top

All H atoms were included at calculated positions with their positional and isotropic displacement parameters constrained.

Computing details top

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1999a); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure Corporation, 1999b); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON for Windows (Spek, 1999); software used to prepare material for publication: TEXSAN for Windows.

Figures top
[Figure 1] Fig. 1. The molecular configuration and atom-numbering scheme. Atoms are shown as 30% probability ellipsoids.
racemic 7-oxabicyclo[2.2.1]heptane-5-exo-iodo-6-endo-hydroxy-2-endo- carboxylic acid-γ-lactone top
Crystal data top
C7H7IO3F(000) = 504
Mr = 266.04Dx = 2.244 Mg m3
Monoclinic, P21/cMelting point = 430–430.5 K
Hall symbol: -P 2ybcMo Kα radiation, λ = 0.71069 Å
a = 5.9896 (11) ÅCell parameters from 25 reflections
b = 15.5307 (15) Åθ = 19.5–20.0°
c = 8.8471 (11) ŵ = 4.02 mm1
β = 106.934 (12)°T = 295 K
V = 787.3 (2) Å3Prism, colourless
Z = 40.30 × 0.25 × 0.25 mm
Data collection top
Rigaku AFC-7R
diffractometer
1470 reflections with I > 2σ(I)
Radiation source: Rigaku rotating anodeRint = 0.024
Graphite monochromatorθmax = 27.5°, θmin = 2.6°
ω–2θ scansh = 07
Absorption correction: ψ scan
TEXSAN for Windows (Molecular Structure Corporation, 1999b)
k = 018
Tmin = 0.379, Tmax = 0.433l = 1111
2170 measured reflections3 standard reflections every 150 reflections
1787 independent reflections intensity decay: 1.2%
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)] = 0.029H-atom parameters not refined
wR(F2) = 0.077 w = 1/[σ2(Fo2) + (0.0265P)2 + 2.3302P]
where P = (Fo2 + 2Fc2)/3
S = 1.06(Δ/σ)max < 0.001
1787 reflectionsΔρmax = 0.43 e Å3
101 parametersΔρmin = 0.35 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0208 (9)
Crystal data top
C7H7IO3V = 787.3 (2) Å3
Mr = 266.04Z = 4
Monoclinic, P21/cMo Kα radiation
a = 5.9896 (11) ŵ = 4.02 mm1
b = 15.5307 (15) ÅT = 295 K
c = 8.8471 (11) Å0.30 × 0.25 × 0.25 mm
β = 106.934 (12)°
Data collection top
Rigaku AFC-7R
diffractometer
1470 reflections with I > 2σ(I)
Absorption correction: ψ scan
TEXSAN for Windows (Molecular Structure Corporation, 1999b)
Rint = 0.024
Tmin = 0.379, Tmax = 0.4333 standard reflections every 150 reflections
2170 measured reflections intensity decay: 1.2%
1787 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0290 restraints
wR(F2) = 0.077H-atom parameters not refined
S = 1.06Δρmax = 0.43 e Å3
1787 reflectionsΔρmin = 0.35 e Å3
101 parameters
Special details top

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
I50.37953 (5)0.120015 (19)0.43653 (3)0.04320 (15)
O70.1560 (6)0.1964 (2)0.6664 (4)0.0462 (8)
O210.1268 (7)0.0923 (3)1.1547 (4)0.0574 (10)
O220.1408 (6)0.1338 (2)0.9350 (4)0.0434 (7)
C10.0983 (9)0.2124 (3)0.8093 (5)0.0405 (10)
C20.2448 (8)0.1497 (3)0.9326 (5)0.0427 (10)
C210.0852 (9)0.1224 (3)1.0257 (5)0.0415 (10)
C30.2780 (8)0.0753 (3)0.8230 (6)0.0456 (11)
C40.1197 (8)0.1048 (3)0.6606 (6)0.0389 (10)
C50.1340 (7)0.0979 (3)0.6653 (5)0.0321 (8)
C60.1421 (8)0.1700 (3)0.7840 (5)0.0360 (9)
H10.10750.27100.84150.049*
H20.38760.17370.99560.051*
H40.15000.07710.57280.047*
H50.17880.03690.70150.069*
H60.26740.20900.74370.043*
H310.22750.02170.85340.055*
H320.43610.07060.82300.055*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
I50.0509 (2)0.0414 (2)0.03273 (19)0.00294 (13)0.00500 (13)0.00199 (12)
O70.060 (2)0.0389 (18)0.0461 (18)0.0132 (15)0.0254 (16)0.0028 (14)
O210.077 (3)0.050 (2)0.0367 (18)0.0092 (19)0.0036 (17)0.0077 (16)
O220.0456 (18)0.053 (2)0.0335 (16)0.0078 (15)0.0136 (13)0.0005 (14)
C10.055 (3)0.030 (2)0.037 (2)0.0102 (19)0.016 (2)0.0034 (17)
C20.036 (2)0.045 (3)0.043 (2)0.0109 (19)0.0041 (19)0.006 (2)
C210.053 (3)0.031 (2)0.035 (2)0.0092 (19)0.0057 (19)0.0027 (17)
C30.032 (2)0.048 (3)0.053 (3)0.0011 (19)0.007 (2)0.003 (2)
C40.043 (2)0.033 (2)0.043 (2)0.0021 (18)0.016 (2)0.0067 (17)
C50.031 (2)0.032 (2)0.0299 (19)0.0008 (16)0.0039 (15)0.0016 (16)
C60.043 (2)0.032 (2)0.033 (2)0.0042 (18)0.0114 (18)0.0020 (17)
Geometric parameters (Å, º) top
I5—C52.155 (4)C2—C31.558 (7)
O7—C11.427 (5)C2—H20.95
O7—C41.438 (5)C3—C41.542 (7)
O21—C211.190 (6)C3—H310.95
O22—C211.369 (6)C3—H320.95
O22—C61.447 (5)C4—C51.536 (6)
C1—C21.533 (7)C4—H40.95
C1—C61.539 (6)C5—C61.545 (6)
C1—H10.95C5—H51.06
C2—C211.494 (7)C6—H60.95
C1—O7—C497.5 (3)C2—C3—H32111
C21—O22—C6109.3 (3)H31—C3—H32109
O7—C1—C2106.5 (4)O7—C4—C5102.0 (3)
O7—C1—C6104.7 (3)O7—C4—C3102.4 (4)
C2—C1—C698.6 (3)C5—C4—C3107.4 (4)
O7—C1—H1115O7—C4—H4115
C2—C1—H1115C5—C4—H4115
C6—C1—H1115C3—C4—H4115
C21—C2—C1104.3 (4)C4—C5—C6101.2 (3)
C21—C2—C3110.5 (4)C4—C5—I5111.9 (3)
C1—C2—C3100.3 (4)C6—C5—I5112.0 (3)
C21—C2—H2114C4—C5—H5114
C1—C2—H2114C6—C5—H5112
C3—C2—H2114I5—C5—H5105
O21—C21—O22120.6 (5)O22—C6—C1106.1 (3)
O21—C21—C2130.6 (5)O22—C6—C5110.7 (3)
O22—C21—C2108.8 (4)C1—C6—C5101.3 (3)
C4—C3—C2101.8 (4)O22—C6—H6113
C4—C3—H31111C1—C6—H6113
C2—C3—H31111C5—C6—H6113
C4—C3—H32111
C4—O7—C1—C251.6 (4)C2—C3—C4—O737.9 (4)
C4—O7—C1—C652.3 (4)C2—C3—C4—C569.1 (4)
O7—C1—C2—C21141.7 (4)O7—C4—C5—C638.8 (4)
C6—C1—C2—C2133.4 (4)C3—C4—C5—C668.5 (4)
O7—C1—C2—C327.2 (4)O7—C4—C5—I580.6 (3)
C6—C1—C2—C381.1 (4)C3—C4—C5—I5172.0 (3)
C6—O22—C21—O21179.2 (4)C21—O22—C6—C121.3 (4)
C6—O22—C21—C21.3 (5)C21—O22—C6—C587.8 (4)
C1—C2—C21—O21159.1 (5)O7—C1—C6—O22143.1 (3)
C3—C2—C21—O2193.9 (6)C2—C1—C6—O2233.4 (4)
C1—C2—C21—O2223.3 (5)O7—C1—C6—C527.4 (4)
C3—C2—C21—O2283.6 (5)C2—C1—C6—C582.3 (4)
C21—C2—C3—C4103.1 (4)C4—C5—C6—O22105.4 (4)
C1—C2—C3—C46.5 (4)I5—C5—C6—O22135.2 (3)
C1—O7—C4—C556.4 (4)C4—C5—C6—C16.8 (4)
C1—O7—C4—C354.7 (4)I5—C5—C6—C1112.6 (3)

Experimental details

Crystal data
Chemical formulaC7H7IO3
Mr266.04
Crystal system, space groupMonoclinic, P21/c
Temperature (K)295
a, b, c (Å)5.9896 (11), 15.5307 (15), 8.8471 (11)
β (°) 106.934 (12)
V3)787.3 (2)
Z4
Radiation typeMo Kα
µ (mm1)4.02
Crystal size (mm)0.30 × 0.25 × 0.25
Data collection
DiffractometerRigaku AFC-7R
diffractometer
Absorption correctionψ scan
TEXSAN for Windows (Molecular Structure Corporation, 1999b)
Tmin, Tmax0.379, 0.433
No. of measured, independent and
observed [I > 2σ(I)] reflections
2170, 1787, 1470
Rint0.024
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.029, 0.077, 1.06
No. of reflections1787
No. of parameters101
H-atom treatmentH-atom parameters not refined
Δρmax, Δρmin (e Å3)0.43, 0.35

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1999a), MSC/AFC Diffractometer Control Software, TEXSAN for Windows (Molecular Structure Corporation, 1999b), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), PLATON for Windows (Spek, 1999), TEXSAN for Windows.

 

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