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The title compound, C14H16O4, was obtained during the synthesis of 2,6-disubstituted azulene derivatives. In the partially reduced azulene skeleton, the absence of a H atom at the ester substitutent position of the seven-membered ring, as well as lengthened double bonds, indicate a conjugative stabilized system with two overlaid tautomers.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105029744/fa1151sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270105029744/fa1151Isup2.hkl
Contains datablock I

CCDC reference: 290577

Comment top

The synthesis of the azulene skeleton has received a good deal of attention over the past few decades (Nefedov, 1973). Luhowy & Keehn (1977) synthesized azulenophane in order to study the charge-transfer interaction, and later Zindel et al. (1996) reported the synthesis of 2,6-substituted push–pull azulene. Recently, Mori et al. (2003) synthesized the 1,3-diazaazulene skeleton and described the mesomorphic properties of its various derivatives. Our primary interest was in synthesizing the perhydroazulene skeleton and in studying the various new materials based on this system. During our work on synthesizing the core skeleton, we employed various synthetic strategies to obtain 2,6-disubstituted perhydroazulene derivatives. We employed a slightly modified synthetic strategy as reported by Zindel et al. (1996) to obtain the title compound, (I), in order to investigate its structural and stereochemical features for input into further studies.

We prepared compound (I) by adding formic acid to its diester and stirring the mixture at room temperature for 15 h. Compound (I), obtained first as a light-coloured solid, was recrystallized from hexane to obtain colourless irregular crystals. The structure analysis revealed an azulene framework which was partially hydrogenated at the pentacyclic subunit. The geometric parameters of the seven-membered ring further revealed the presence of disorder between two tautomers. Their structures, shown as two overlaid molecules in Fig. 1, were refined with a disorder model involving atoms C5, C6, C8 and C9, and C5A, C6A, C8A and C9A [with 53(s.u.?):47(s.u.?)% refined occupancy, minor sites linked with open bonds in Fig. 1].

We did not find an H atom at C7 in the difference Fourier map, but did observe two H atoms at each of C5A and C9, as well as only one H atom at C5 and at C9A. Due to the disorder of the seven-membered ring, these H atoms were included in the refinement in calculated positions which were re-idealized after every refinement run.

The disorder of the two tautomers is evident in an analysis of selected geometric parameters, listed in Table 1. The average value of the distances C5—C6, C5A—C6A, C8—C9 and C8A—C9A [1.392 (5) Å] is longer by about 0.07 Å than the average for chemically equivalent olefinic bonds (Allen et al., 1995). For comparison, the C4C10 double bond has a length of 1.337 (2) Å, which is in the expected range. Furthermore, the average value of 1.412 (4) Å for the bonds C6—C7, C6A—C7, C7—C8 and C7—C8A is about 0.05 Å shorter than comparable single-bond lengths tabulated by Allen et al. (1995). In addition, a very `flat' conformation at the top atom, C7, was detected (selected torsion angles are given in Table 1), thus indicating conjugative interaction of the π system with the ester substituent.

In the extended structure of (I), stabilizing hydrogen bonds were found [O4—H4O···O3i 1.74 (3) Å, O4···O3i 2.635 (3) Å, O4—H4O···O3i 176.9 (2)°; symmetry code: (i) −x,-y + 1,-z − 1], mediating aggregation of the azulene derivatives into dimeric pairs across a crystallographic centre of symmetry.

Experimental top

A solution of the diester of (I) (1.0 mmol) in formic acid (50 ml) was stirred at room temperature for 15 h. The solvent was removed under reduced pressure and the crude product, originally obtained as a slightly coloured solid, was recrystallized from hexane, to give a 95% yield of (I) as colourless irregular crystals.

Refinement top

Each of the atoms C5, C6, C8 and C9 was refined at two positions with 53(s.u.?):47(s.u.?)% refined occupancy. The displacement parameters of their disordered positions were only refined isotropically because some of the disorder sites are rather close together. Their positions were not initially located as separate sites in a difference map, but were rather generated by splitting the atomic positions with large anisotropic displacement parameters, as per a suggestion by SHELXTL (Bruker, 2001). The H atom of the carboxylic acid group was located in a difference Fourier map and refined isotropically. All other H atoms were found in a difference map but then placed in calculated positions and included in the refinement with Uiso(H) = 1.2Ueq(C) [1.5Ueq(Cmethyl)], and their positions were re-idealized before each refinement cycle. The C—H bond distances of 0.95–0.99 Å were established according to criteria described in the SHELXTL manual (Bruker, 2001), with an increase of 0.01 or 0.02 Å for low-temperature refinement.

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SMART; data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Bruker, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. The unshaded bonds indicate the minor sites of two overlaid tautomeric molecules. Displacement ellipsoids are drawn at the ??% probability level [Please complete] and H atoms are shown as small spheres of arbitrary radii.
(RS)-1,2,3,4-tetrahydroazulene-2,6-dicarboxylic acid 6-ethyl ester top
Crystal data top
C14H16O4F(000) = 528
Mr = 248.27Dx = 1.375 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 4.1002 (4) ÅCell parameters from 4258 reflections
b = 36.118 (4) Åθ = 2.3–28.3°
c = 8.3164 (8) ŵ = 0.10 mm1
β = 103.157 (2)°T = 100 K
V = 1199.2 (2) Å3Irregular, colourless
Z = 40.18 × 0.15 × 0.14 mm
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer
2953 independent reflections
Radiation source: fine-focus sealed tube2710 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.031
ϕ and ω scansθmax = 28.3°, θmin = 2.3°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
h = 55
Tmin = 0.982, Tmax = 0.986k = 4848
11969 measured reflectionsl = 1111
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.061Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.136H atoms treated by a mixture of independent and constrained refinement
S = 1.17 w = 1/[σ2(Fo2) + (0.0468P)2 + 0.8094P]
where P = (Fo2 + 2Fc2)/3
2953 reflections(Δ/σ)max = 0.001
165 parametersΔρmax = 0.37 e Å3
0 restraintsΔρmin = 0.22 e Å3
Crystal data top
C14H16O4V = 1199.2 (2) Å3
Mr = 248.27Z = 4
Monoclinic, P21/cMo Kα radiation
a = 4.1002 (4) ŵ = 0.10 mm1
b = 36.118 (4) ÅT = 100 K
c = 8.3164 (8) Å0.18 × 0.15 × 0.14 mm
β = 103.157 (2)°
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer
2953 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
2710 reflections with I > 2σ(I)
Tmin = 0.982, Tmax = 0.986Rint = 0.031
11969 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0610 restraints
wR(F2) = 0.136H atoms treated by a mixture of independent and constrained refinement
S = 1.17Δρmax = 0.37 e Å3
2953 reflectionsΔρmin = 0.22 e Å3
165 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. The highest peak is located 0.73 Å from atom C2 and the deepest hole 0.28 Å from atom H9A.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
O10.4078 (4)0.66224 (4)0.55926 (16)0.0350 (4)
O20.1767 (3)0.70239 (3)0.36272 (14)0.0231 (3)
O30.0919 (3)0.54329 (3)0.45087 (15)0.0240 (3)
O40.1732 (4)0.50371 (3)0.31913 (16)0.0256 (3)
C10.0660 (4)0.60205 (4)0.22418 (19)0.0186 (3)
H1A0.19910.60250.30970.022*
H1B0.12490.61940.25640.022*
C20.0563 (4)0.56264 (4)0.20010 (19)0.0169 (3)
H20.29470.56420.19060.020*
C30.1595 (4)0.54850 (4)0.0321 (2)0.0197 (3)
H3A0.01680.53750.03670.024*
H3B0.32500.52990.04960.024*
C40.3306 (4)0.58299 (4)0.04658 (19)0.0173 (3)
C50.5131 (14)0.58290 (11)0.2175 (5)0.0182 (11)*0.531 (11)
H50.60090.56000.26410.022*0.531 (11)
C60.5676 (14)0.61343 (10)0.3160 (4)0.0187 (9)*0.531 (11)
H60.72420.61100.41900.022*0.531 (11)
C5A0.5828 (16)0.58411 (13)0.2095 (6)0.0189 (13)*0.469 (11)
H5A10.61070.55900.25860.023*0.469 (11)
H5A20.80250.59240.19210.023*0.469 (11)
C6A0.4663 (15)0.61007 (12)0.3233 (5)0.0191 (10)*0.469 (11)
H6A0.42640.60130.42480.023*0.469 (11)
C70.4146 (5)0.64811 (5)0.2800 (2)0.0239 (4)
C80.4636 (14)0.66424 (10)0.1358 (5)0.0174 (9)*0.531 (11)
H80.49710.69030.14060.021*0.531 (11)
C90.4708 (15)0.64762 (11)0.0163 (5)0.0193 (10)*0.531 (11)
H9A0.70770.64290.01840.023*0.531 (11)
H9B0.38150.66560.10510.023*0.531 (11)
C8A0.3647 (16)0.66551 (12)0.1212 (5)0.0178 (10)*0.469 (11)
H8A0.31380.69120.11670.021*0.469 (11)
C9A0.3820 (15)0.64958 (12)0.0189 (5)0.0170 (11)*0.469 (11)
H9C0.46520.66350.09790.020*0.469 (11)
C100.2797 (4)0.61184 (4)0.05693 (19)0.0181 (3)
C110.3359 (4)0.67066 (5)0.4162 (2)0.0189 (3)
C120.0872 (5)0.72496 (5)0.4898 (2)0.0239 (4)
H12A0.29140.73330.56960.029*
H12B0.05180.71050.55020.029*
C130.1056 (6)0.75768 (5)0.4068 (3)0.0330 (4)
H13A0.03620.77210.34980.049*
H13B0.17420.77320.48990.049*
H13C0.30470.74910.32660.049*
C140.0382 (4)0.53615 (4)0.33691 (19)0.0168 (3)
H4O0.148 (6)0.4884 (7)0.400 (3)0.044 (7)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0581 (10)0.0273 (7)0.0167 (6)0.0088 (6)0.0022 (6)0.0013 (5)
O20.0332 (7)0.0204 (6)0.0147 (6)0.0036 (5)0.0034 (5)0.0034 (4)
O30.0376 (7)0.0178 (6)0.0192 (6)0.0039 (5)0.0120 (5)0.0040 (5)
O40.0411 (8)0.0176 (6)0.0218 (6)0.0073 (5)0.0147 (5)0.0065 (5)
C10.0267 (8)0.0138 (7)0.0140 (7)0.0021 (6)0.0021 (6)0.0008 (6)
C20.0201 (7)0.0155 (7)0.0151 (7)0.0012 (6)0.0039 (6)0.0020 (6)
C30.0270 (8)0.0166 (7)0.0150 (7)0.0003 (6)0.0038 (6)0.0007 (6)
C40.0201 (7)0.0165 (7)0.0155 (7)0.0026 (6)0.0042 (6)0.0013 (6)
C70.0280 (9)0.0232 (8)0.0204 (8)0.0010 (7)0.0055 (7)0.0054 (6)
C100.0225 (8)0.0166 (7)0.0152 (7)0.0011 (6)0.0045 (6)0.0027 (6)
C110.0196 (8)0.0196 (8)0.0169 (7)0.0040 (6)0.0030 (6)0.0019 (6)
C120.0296 (9)0.0238 (8)0.0186 (8)0.0009 (7)0.0062 (7)0.0071 (6)
C130.0396 (11)0.0259 (9)0.0337 (10)0.0072 (8)0.0086 (8)0.0043 (8)
C140.0180 (7)0.0161 (7)0.0148 (7)0.0019 (6)0.0005 (6)0.0008 (6)
Geometric parameters (Å, º) top
O1—C111.198 (2)C5A—C6A1.486 (7)
O2—C111.344 (2)C5A—H5A10.9900
O2—C121.447 (2)C5A—H5A20.9900
O3—C141.216 (2)C6A—C71.424 (4)
O4—C141.318 (2)C6A—H6A0.9500
O4—H4O0.89 (3)C7—C81.388 (4)
C1—C101.508 (2)C7—C8A1.435 (5)
C1—C21.537 (2)C7—C111.488 (2)
C1—H1A0.9900C8—C91.406 (5)
C1—H1B0.9900C8—H80.9500
C2—C141.501 (2)C9—C101.509 (4)
C2—C31.560 (2)C9—H9A0.9900
C2—H21.0000C9—H9B0.9900
C3—C41.504 (2)C8A—C9A1.315 (6)
C3—H3A0.9900C8A—H8A0.9500
C3—H3B0.9900C9A—C101.440 (4)
C4—C101.337 (2)C9A—H9C0.9500
C4—C51.448 (4)C12—C131.500 (3)
C4—C5A1.506 (5)C12—H12A0.9900
C5—C61.362 (5)C12—H12B0.9900
C5—H50.9500C13—H13A0.9800
C6—C71.403 (4)C13—H13B0.9800
C6—H60.9500C13—H13C0.9800
C11—O2—C12115.08 (13)C8—C7—C11121.8 (2)
C14—O4—H4O110.1 (17)C6—C7—C11119.4 (2)
C10—C1—C2103.61 (13)C6A—C7—C11112.4 (2)
C10—C1—H1A111.0C8A—C7—C11116.8 (2)
C2—C1—H1A111.0C7—C8—C9129.4 (3)
C10—C1—H1B111.0C7—C8—H8115.3
C2—C1—H1B111.0C9—C8—H8115.3
H1A—C1—H1B109.0C8—C9—C10116.8 (3)
C14—C2—C1114.68 (13)C8—C9—H9A108.1
C14—C2—C3110.75 (13)C10—C9—H9A108.1
C1—C2—C3106.53 (13)C8—C9—H9B108.1
C14—C2—H2108.2C10—C9—H9B108.1
C1—C2—H2108.2H9A—C9—H9B107.3
C3—C2—H2108.2C9A—C8A—C7126.8 (4)
C4—C3—C2103.41 (13)C9A—C8A—H8A116.6
C4—C3—H3A111.1C7—C8A—H8A116.6
C2—C3—H3A111.1C8A—C9A—C10122.5 (4)
C4—C3—H3B111.1C8A—C9A—H9C118.8
C2—C3—H3B111.1C10—C9A—H9C118.8
H3A—C3—H3B109.0C4—C10—C9A126.9 (2)
C10—C4—C5127.1 (2)C4—C10—C1112.57 (14)
C10—C4—C3112.09 (14)C9A—C10—C1120.3 (2)
C5—C4—C3120.7 (2)C4—C10—C9121.7 (2)
C10—C4—C5A122.2 (2)C1—C10—C9124.81 (19)
C3—C4—C5A124.8 (2)O1—C11—O2122.42 (15)
C6—C5—C4124.5 (3)O1—C11—C7124.73 (16)
C6—C5—H5117.7O2—C11—C7112.84 (14)
C4—C5—H5117.7O2—C12—C13107.62 (14)
C5—C6—C7126.2 (4)O2—C12—H12A110.2
C5—C6—H6116.9C13—C12—H12A110.2
C7—C6—H6116.9O2—C12—H12B110.2
C6A—C5A—C4109.6 (4)C13—C12—H12B110.2
C6A—C5A—H5A1109.8H12A—C12—H12B108.5
C4—C5A—H5A1109.8C12—C13—H13A109.5
C6A—C5A—H5A2109.8C12—C13—H13B109.5
C4—C5A—H5A2109.8H13A—C13—H13B109.5
H5A1—C5A—H5A2108.2C12—C13—H13C109.5
C7—C6A—C5A119.9 (4)H13A—C13—H13C109.5
C7—C6A—H6A120.1H13B—C13—H13C109.5
C5A—C6A—H6A120.1O3—C14—O4123.06 (14)
C8—C7—C6114.4 (3)O3—C14—C2124.16 (15)
C8—C7—C6A125.5 (3)O4—C14—C2112.77 (14)
C6A—C7—C8A129.6 (3)
C10—C1—C2—C14135.68 (14)C3—C4—C10—C10.1 (2)
C10—C1—C2—C312.79 (16)C5A—C4—C10—C1169.2 (3)
C14—C2—C3—C4138.06 (14)C5—C4—C10—C912.7 (5)
C1—C2—C3—C412.74 (17)C3—C4—C10—C9169.8 (3)
C2—C3—C4—C108.04 (18)C8A—C9A—C10—C439.6 (6)
C2—C3—C4—C5169.7 (3)C8A—C9A—C10—C1134.6 (4)
C2—C3—C4—C5A177.0 (3)C2—C1—C10—C48.39 (19)
C10—C4—C5—C622.9 (8)C2—C1—C10—C9A166.6 (3)
C3—C4—C5—C6154.5 (5)C2—C1—C10—C9177.7 (3)
C4—C5—C6—C711.2 (10)C8—C9—C10—C453.5 (5)
C10—C4—C5A—C6A69.0 (6)C8—C9—C10—C1138.1 (3)
C3—C4—C5A—C6A123.1 (4)C12—O2—C11—O12.2 (2)
C4—C5A—C6A—C760.6 (7)C12—O2—C11—C7178.59 (14)
C5—C6—C7—C858.1 (8)C8—C7—C11—O1151.3 (3)
C5—C6—C7—C11145.1 (5)C6—C7—C11—O13.7 (4)
C5A—C6A—C7—C8A19.8 (10)C6A—C7—C11—O122.5 (4)
C5A—C6A—C7—C11173.5 (5)C8A—C7—C11—O1169.0 (3)
C6—C7—C8—C938.4 (7)C8—C7—C11—O227.8 (3)
C11—C7—C8—C9165.5 (4)C6—C7—C11—O2177.2 (3)
C7—C8—C9—C1025.7 (6)C6A—C7—C11—O2158.3 (3)
C6A—C7—C8A—C9A5.6 (9)C8A—C7—C11—O210.2 (3)
C11—C7—C8A—C9A171.8 (4)C11—O2—C12—C13176.49 (15)
C7—C8A—C9A—C1034.0 (8)C1—C2—C14—O37.1 (2)
C3—C4—C10—C9A174.4 (3)C3—C2—C14—O3113.49 (18)
C5A—C4—C10—C9A16.3 (5)C1—C2—C14—O4174.21 (14)
C5—C4—C10—C1177.7 (3)C3—C2—C14—O465.21 (18)

Experimental details

Crystal data
Chemical formulaC14H16O4
Mr248.27
Crystal system, space groupMonoclinic, P21/c
Temperature (K)100
a, b, c (Å)4.1002 (4), 36.118 (4), 8.3164 (8)
β (°) 103.157 (2)
V3)1199.2 (2)
Z4
Radiation typeMo Kα
µ (mm1)0.10
Crystal size (mm)0.18 × 0.15 × 0.14
Data collection
DiffractometerBruker SMART APEX CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2003)
Tmin, Tmax0.982, 0.986
No. of measured, independent and
observed [I > 2σ(I)] reflections
11969, 2953, 2710
Rint0.031
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.061, 0.136, 1.17
No. of reflections2953
No. of parameters165
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.37, 0.22

Computer programs: SMART (Bruker, 2001), SMART, SAINT (Bruker, 2001), SHELXTL (Bruker, 2001), SHELXTL, ORTEP-3 for Windows (Farrugia, 1997).

Selected geometric parameters (Å, º) top
C4—C101.337 (2)C7—C81.388 (4)
C4—C51.448 (4)C7—C8A1.435 (5)
C4—C5A1.506 (5)C8—C91.406 (5)
C5—C61.362 (5)C9—C101.509 (4)
C6—C71.403 (4)C8A—C9A1.315 (6)
C5A—C6A1.486 (7)C9A—C101.440 (4)
C6A—C71.424 (4)
C10—C4—C5—C622.9 (8)C6A—C7—C8A—C9A5.6 (9)
C4—C5—C6—C711.2 (10)C11—C7—C8A—C9A171.8 (4)
C10—C4—C5A—C6A69.0 (6)C7—C8A—C9A—C1034.0 (8)
C4—C5A—C6A—C760.6 (7)C5A—C4—C10—C9A16.3 (5)
C5—C6—C7—C858.1 (8)C5—C4—C10—C912.7 (5)
C5—C6—C7—C11145.1 (5)C8A—C9A—C10—C439.6 (6)
C5A—C6A—C7—C8A19.8 (10)C8—C9—C10—C453.5 (5)
C5A—C6A—C7—C11173.5 (5)C8—C7—C11—O1151.3 (3)
C6—C7—C8—C938.4 (7)C6—C7—C11—O13.7 (4)
C11—C7—C8—C9165.5 (4)C6A—C7—C11—O122.5 (4)
C7—C8—C9—C1025.7 (6)C8A—C7—C11—O1169.0 (3)
 

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