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The title compound, C12H20O3, (IV), the ethyl ester of which is an intermediate in the synthesis of a compound reported to be highly estrogenic, has been prepared. After the initial steps reported for the synthesis of this ester intermediate were followed, it was converted into the crystalline acid, (IV), for X-ray analysis. It was verified that (IV) was racemic when prepared. X-ray analysis showed that anti-hydrogenation of the double bond had occurred in the synthesis, making the orientation of the carboxyl group cis to the 2-methyl group and trans to the 3-ethyl group. NMR spectroscopy showed that the stereochemistry of (IV) was identical with that of its ester precursor. While the earlier report did not note the stereochemistry of this ester, it pointed out that the estrogenic product derived from it possessed the opposite carboxyl-2-methyl orientation, i.e. trans, although no X-ray analysis was performed. In the light of these results and the importance of correlating biological activity with compound structure, the unequivocal characterization of the highly estrogenic compound is warranted.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102000252/sk1530sup1.cif
Contains datablocks global, IV

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102000252/sk1530IVsup2.hkl
Contains datablock IV

CCDC reference: 183004

Comment top

Some years ago, Crenshaw et al. (1974) reported syntheses of a series of p-methoxyphenylalkylcyclohexanecarboxylic and -cyclohexenecarboxylic acids, some of which they found to be highly estrogenic. Although they showed these compounds to be uterotropically potent, they presumed them to possess high estrogen-receptor binding affinity as well, but they did not test this property. In contrast, our more recent studies of estrogenic carboxylic acids have revealed that they exhibit the paradox of high uterotropic activity with very poor binding affinity for estrogen receptors (Meyers et al., 1988, 1997, 2000; Banz et al., 1998; Robinson et al., 1999; Hou & Meyers, 2000), hence our interest in preparing the Crenshaw compounds, unequivocally determining their structures and correlating them with their uterotropic activities and estrogen-receptor binding affinities. The structure of one of these, the title compound, (IV), is presented here. \sch

The syntheses are shown in the Scheme. We repeated the methods used by Crenshaw et al. (1974) to prepare the initial ester intermediates (I), (II) and (III), then hydrolyzed ester (III) with aqueous HBr to give (IV). The Crenshaw group treated (III) with a Grignard reagent and hydrolyzed the product under acidic conditions to provide their carboxylic acid estrogen, (V), also shown in the Scheme. Unlike ester (III), an oil, the corresponding carboxylic acid, (IV) is crystalline, permitting its diastereomeric structure to be unequivocally characterized by X-ray analysis.

The structure of (IV) is shown in Fig. 1. The space group for this chiral structure is P212121. However, (IV) was racemic when prepared by polarimetric analysis as well as by 1H NMR shift analysis in the presence of a chiral amine. Thus, either the crystal used is the result of spontaneous resolution which produced a mechanical mixture of pure enantiomers (a `conglomerate'; Jacques et al., 1981), or it is an inversion twin (Flack & Bernardinelli, 1999). The latter choice is the more common but we cannot be sure, since the Flack parameter cannot discriminate in this case (Flack & Bernardinelli, 2000).

Fig. 1 shows the trans orientation of the C2 methyl group with respect to the C3 ethyl group, indicating that antihydrogenation of the double bond has occurred in converting (II) to (III), which is also responsible for the cis orientation of the C1 carboxyl group with respect to the C2 methyl group, likewise clearly exhibited. The stereochemistry of ester (III) is the same as that of its carboxylic acid, (IV), as ascertained from their virtually identical 1H and 13C NMR spectra, the only differences being the resonances of their different carboxyl groups.

The Crenshaw report provided no geometric characterization for their ester (III). In the absence of an unforseen isomerization, it is reasonable to believe that their Grignard reaction at the carbonyl group of (III), followed by acidification, dehydration to form the C3C4 double bond, and ester hydrolysis, would provide estrogenic carboxylic acid (V) without altering the cis orientation of the C1 carboxyl group with respect to the C2 methyl group. However, on the basis of the NMR H1—H2 coupling constant exhibited by (V), they reported a trans orientation for the C1 carboxyl with respect to the C2 methyl. No X-ray crystal-structure analysis was reported. In the light of these results and the importance of correlating biological activity with compound structure, X-ray characterization of crystalline (V) is warranted so that the structure can be correlated with its uterotropic activity and receptor-binding affinity.

Fig. 1 also shows that (IV) has the chair conformation, in which the C1 carboxyl group is axial and the C2 methyl group equatorial, providing the cis configurations of these groups, while the C3 ethyl group is also equatorial, making it trans to both of these groups. Thus, the C6—C1—C2—C8 torsion angle subtended by the C2 methyl group with the ring is essentially linear [-179.0 (2)°], while the C1—C2—C3—C9 torsion angle subtended by the C3 ethyl group with the ring is somewhat less than linear [171.5 (2)°].

Bond distances and angles of interest are given in Table 1. It is noted that, while the angle subtended by the ring with all but one of the substituents is between 109.6 (2) and 111.8 (2)°, that involving the C3 ethyl group, C2—C3—C9, is 114.0 (2)°, suggesting a steric repulsion between this equatorial group and the vicinal equatorial C2 methyl group.

The molecular packing (Fig. 2) shows that the molecules of (IV) form infinite one-dimensional chains parallel to the b axis via intermolecular hydrogen bonding between the carbonyl O atom and the carboxyl H atom. Table 2 lists the hydrogen-bond geometry.

Experimental top

Compound (I) was synthesized following the method reported by Surmatis et al. (1970) and converted sequentially into compounds (II) and (III), as reported by Crenshaw et al. (1974). Via hydrolysis in refluxing 48% HBr containing a catalytic amount of (n-Bu)4NBr, we converted (III) into (IV). White crystals of (IV) were recrystallized twice from hexane (m.p. 394.8–396.2 K). 1H NMR (CDCl3, δ, p.p.m.): 0.881 (t, J = 7.5 Hz, 3H), 0.986 (s, 3H), 1.096 (s, 3H), 1.123 (d, J = 6.9 Hz, 3H), 1.512 (m, 1H), 1.710 (m, 1H), 1.984 (dd, J = 13.5 and 1.8 Hz, 1H), 2.158 (m, 1H), 2.479 (dd, J = 4.5 and 1.5 Hz, 1H), 2.657 (m, 1H), 2.963 (d, J = 13.8 Hz, 1H); 13C NMR (CDCl3, δ, p.p.m.): 10.51, 17.65, 17.88, 27.87, 28.83, 33.39, 36.44, 50.26, 50.93, 56.67, 179.66, 220.97. The determination of the racemic nature of (IV) as prepared was conducted as follows: (i) an absolute ethanol solution of 0.046 mol l-1 of (IV), as prepared, exhibited an optical rotation of 0.0; (ii) the 1H NMR (CDCl3) resonance of H5 cis to the carboxyl of (IV), as prepared, δ 2.963 (d), became δ 3.032 (d) and δ 2.997 (d) in an approximately equimolar solution with (S)-(-)-1-phenylethylamine (Aldrich); (iii) likewise, the resonance of H5 trans to carboxyl, δ 1.984 (dd), became δ 1.897 and δ 1.863 in the same solution with (S)-(-)-1-phenylethylamine.

Refinement top

The absolute configuration of the molecule could not be determined because of the lack of heavy atoms. The rotational orientations of the methyl and hydroxyl H atoms were refined by the circular Fourier method available in SHELXL97 (Sheldrick, 1997). All H atoms were treated as riding, with C—H = 0.96–0.98 Å and O—H = 0.82 Å. Are these the correct constraints?

Computing details top

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1996); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: PROCESS in TEXSAN (Molecular Structure Corporation, 1997); program(s) used to solve structure: SIR92 (Burla, 1989); program(s) used to refine structure: LS in TEXSAN and SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-III (Farrugia, 1997); software used to prepare material for publication: TEXSAN, SHELXL97 and PLATON (Spek, 2000).

Figures top
[Figure 1] Fig. 1. The molecular structure and atom-numbering scheme for (IV), with displacement ellipsoids at the 50% probability level. H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. The molecular packing and hydrogen bonding in (IV), as viewed down the c axis. Note the infinite one-dimensional molecular chains parallel to the b axis [symmetry code: (i) -x, y - 1/2, 3/2 - z].
2-cis-3-trans-3-Ethyl-2,6,6-trimethyl-4-oxocyclohexanecarboxylic acid top
Crystal data top
C12H20O3Dx = 1.173 Mg m3
Mr = 212.28Melting point = 394.8–396.2 K
Orthorhombic, P212121Mo Kα radiation, λ = 0.71069 Å
Hall symbol: P 2ac 2abCell parameters from 25 reflections
a = 13.716 (3) Åθ = 9.6–9.9°
b = 14.103 (3) ŵ = 0.08 mm1
c = 6.214 (4) ÅT = 296 K
V = 1202.0 (9) Å3Irregular fragment, colorless
Z = 40.41 × 0.33 × 0.27 mm
F(000) = 464
Data collection top
Rigaku AFC-5S
diffractometer
Rint = 0.025
Radiation source: fine-focus sealed tubeθmax = 25.1°, θmin = 2.1°
Graphite monochromatorh = 016
ω scansk = 016
2313 measured reflectionsl = 77
1265 independent reflections3 standard reflections every 100 reflections
890 reflections with I > 2σ(I) intensity decay: 0.7%
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)] = 0.034Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.092H-atom parameters constrained
S = 1.03 w = 1/[σ2(Fo2) + (0.0509P)2]
where P = (Fo2 + 2Fc2)/3
1265 reflections(Δ/σ)max < 0.001
141 parametersΔρmax = 0.10 e Å3
0 restraintsΔρmin = 0.13 e Å3
Crystal data top
C12H20O3V = 1202.0 (9) Å3
Mr = 212.28Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 13.716 (3) ŵ = 0.08 mm1
b = 14.103 (3) ÅT = 296 K
c = 6.214 (4) Å0.41 × 0.33 × 0.27 mm
Data collection top
Rigaku AFC-5S
diffractometer
Rint = 0.025
2313 measured reflections3 standard reflections every 100 reflections
1265 independent reflections intensity decay: 0.7%
890 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0340 restraints
wR(F2) = 0.092H-atom parameters constrained
S = 1.03Δρmax = 0.10 e Å3
1265 reflectionsΔρmin = 0.13 e Å3
141 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.00322 (19)0.46507 (17)0.8007 (3)0.0866 (8)
O20.11705 (15)0.37785 (12)0.6441 (3)0.0640 (5)
O30.11480 (14)0.74515 (12)0.5400 (3)0.0668 (6)
C10.06744 (18)0.51509 (15)0.4579 (4)0.0396 (6)
C20.02975 (17)0.52046 (15)0.3359 (4)0.0396 (6)
C30.10728 (17)0.58157 (16)0.4493 (4)0.0406 (6)
C40.06654 (17)0.67269 (17)0.5414 (4)0.0421 (6)
C50.03150 (17)0.66974 (18)0.6450 (5)0.0499 (6)
C60.10828 (17)0.61406 (17)0.5165 (4)0.0439 (6)
C70.05804 (19)0.45200 (17)0.6528 (4)0.0477 (6)
C80.0684 (2)0.42062 (17)0.2848 (5)0.0583 (8)
C90.19889 (18)0.59936 (19)0.3139 (5)0.0572 (7)
C100.1801 (2)0.6456 (2)0.0973 (5)0.0725 (9)
C110.20128 (19)0.6041 (2)0.6514 (5)0.0632 (8)
C120.13336 (19)0.66809 (18)0.3110 (5)0.0565 (7)
H10.11480.48510.36130.047*
H20.10750.34380.74890.096*
H2A0.01600.55100.19760.048*
H30.12900.54430.57350.049*
H5A0.02510.64130.78640.060*
H5B0.05450.73420.66460.060*
H8A0.08900.39040.41550.087*
H8B0.01770.38380.21890.087*
H8C0.12270.42540.18800.087*
H9A0.23150.53920.29020.069*
H9B0.24290.63940.39550.069*
H10A0.14380.70310.11770.109*
H10B0.24120.66000.02920.109*
H10C0.14350.60300.00780.109*
H11A0.24890.56860.57190.095*
H11B0.18640.57160.78300.095*
H11C0.22670.66590.68360.095*
H12A0.16680.72570.34740.085*
H12B0.07450.68300.23460.085*
H12C0.17460.62960.22180.085*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.1171 (18)0.0871 (15)0.0557 (12)0.0325 (14)0.0391 (15)0.0269 (13)
O20.0734 (12)0.0458 (10)0.0728 (12)0.0116 (10)0.0072 (12)0.0237 (10)
O30.0666 (12)0.0465 (10)0.0873 (14)0.0195 (10)0.0200 (12)0.0267 (11)
C10.0448 (13)0.0340 (12)0.0400 (12)0.0035 (10)0.0100 (12)0.0020 (11)
C20.0499 (14)0.0321 (12)0.0368 (12)0.0037 (10)0.0073 (12)0.0021 (11)
C30.0445 (13)0.0389 (12)0.0384 (12)0.0044 (11)0.0052 (12)0.0028 (11)
C40.0453 (13)0.0421 (13)0.0391 (12)0.0042 (12)0.0015 (12)0.0084 (11)
C50.0550 (15)0.0428 (13)0.0519 (14)0.0016 (12)0.0103 (14)0.0108 (13)
C60.0401 (13)0.0410 (13)0.0506 (15)0.0008 (11)0.0019 (12)0.0027 (12)
C70.0565 (15)0.0378 (13)0.0488 (15)0.0035 (12)0.0028 (15)0.0059 (13)
C80.0736 (18)0.0403 (14)0.0611 (16)0.0112 (14)0.0075 (16)0.0137 (14)
C90.0419 (14)0.0549 (16)0.075 (2)0.0084 (12)0.0026 (15)0.0121 (16)
C100.0670 (19)0.085 (2)0.066 (2)0.0071 (16)0.0192 (16)0.0026 (18)
C110.0499 (15)0.0621 (17)0.078 (2)0.0011 (13)0.0132 (16)0.0091 (17)
C120.0535 (15)0.0485 (14)0.0674 (18)0.0076 (13)0.0043 (15)0.0150 (15)
Geometric parameters (Å, º) top
O1—C71.201 (3)C3—H30.9800
O2—C71.323 (3)C5—H5A0.9700
O3—C41.218 (3)C5—H5B0.9700
C1—C71.509 (4)C8—H8A0.9600
C1—C21.535 (3)C8—H8B0.9600
C1—C61.547 (3)C8—H8C0.9600
C2—C81.538 (3)C9—H9A0.9700
C2—C31.539 (3)C9—H9B0.9700
C3—C41.514 (3)C10—H10A0.9600
C3—C91.533 (4)C10—H10B0.9600
C4—C51.491 (3)C10—H10C0.9600
C5—C61.537 (3)C11—H11A0.9600
C6—C121.526 (4)C11—H11B0.9600
C6—C111.533 (4)C11—H11C0.9600
C9—C101.518 (4)C12—H12A0.9600
O2—H20.8200C12—H12B0.9600
C1—H10.9800C12—H12C0.9600
C2—H2A0.9800
C7—C1—C2110.56 (19)C6—C5—H5A108.7
C7—C1—C6112.0 (2)C4—C5—H5B108.7
C2—C1—C6112.71 (19)C6—C5—H5B108.7
C1—C2—C8110.9 (2)H5A—C5—H5B107.6
C1—C2—C3113.67 (19)C2—C8—H8A109.5
C8—C2—C3111.7 (2)C2—C8—H8B109.5
C4—C3—C9111.8 (2)H8A—C8—H8B109.5
C4—C3—C2113.16 (19)C2—C8—H8C109.5
C9—C3—C2114.0 (2)H8A—C8—H8C109.5
O3—C4—C5121.1 (2)H8B—C8—H8C109.5
O3—C4—C3120.6 (2)C10—C9—H9A108.6
C5—C4—C3118.2 (2)C3—C9—H9A108.6
C4—C5—C6114.1 (2)C10—C9—H9B108.6
C12—C6—C11108.4 (2)C3—C9—H9B108.6
C12—C6—C5109.5 (2)H9A—C9—H9B107.6
C11—C6—C5109.4 (2)C9—C10—H10A109.5
C12—C6—C1109.6 (2)C9—C10—H10B109.5
C11—C6—C1110.33 (19)H10A—C10—H10B109.5
C5—C6—C1109.57 (19)C9—C10—H10C109.5
O1—C7—O2122.4 (2)H10A—C10—H10C109.5
O1—C7—C1125.2 (2)H10B—C10—H10C109.5
O2—C7—C1112.4 (2)C6—C11—H11A109.5
C10—C9—C3114.7 (2)C6—C11—H11B109.5
C7—O2—H2109.5H11A—C11—H11B109.5
C7—C1—H1107.1C6—C11—H11C109.5
C2—C1—H1107.1H11A—C11—H11C109.5
C6—C1—H1107.1H11B—C11—H11C109.5
C1—C2—H2A106.7C6—C12—H12A109.5
C8—C2—H2A106.7C6—C12—H12B109.5
C3—C2—H2A106.7H12A—C12—H12B109.5
C4—C3—H3105.7C6—C12—H12C109.5
C9—C3—H3105.7H12A—C12—H12C109.5
C2—C3—H3105.7H12B—C12—H12C109.5
C4—C5—H5A108.7
C7—C1—C2—C852.8 (3)C4—C5—C6—C11172.3 (2)
C6—C1—C2—C8179.0 (2)C4—C5—C6—C151.2 (3)
C7—C1—C2—C373.9 (2)C7—C1—C6—C12169.9 (2)
C6—C1—C2—C352.2 (2)C2—C1—C6—C1264.7 (3)
C1—C2—C3—C442.3 (3)C7—C1—C6—C1150.6 (3)
C8—C2—C3—C4168.6 (2)C2—C1—C6—C11176.0 (2)
C1—C2—C3—C9171.5 (2)C7—C1—C6—C569.9 (2)
C8—C2—C3—C962.2 (3)C2—C1—C6—C555.4 (3)
C9—C3—C4—O313.9 (3)C2—C1—C7—O160.5 (3)
C2—C3—C4—O3144.2 (3)C6—C1—C7—O166.0 (3)
C9—C3—C4—C5169.7 (2)C2—C1—C7—O2118.7 (2)
C2—C3—C4—C539.4 (3)C6—C1—C7—O2114.7 (2)
O3—C4—C5—C6138.6 (3)C4—C3—C9—C1073.0 (3)
C3—C4—C5—C644.9 (3)C2—C3—C9—C1056.9 (3)
C4—C5—C6—C1269.0 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2···O3i0.821.912.712 (3)164
Symmetry code: (i) x, y1/2, z+3/2.

Experimental details

Crystal data
Chemical formulaC12H20O3
Mr212.28
Crystal system, space groupOrthorhombic, P212121
Temperature (K)296
a, b, c (Å)13.716 (3), 14.103 (3), 6.214 (4)
V3)1202.0 (9)
Z4
Radiation typeMo Kα
µ (mm1)0.08
Crystal size (mm)0.41 × 0.33 × 0.27
Data collection
DiffractometerRigaku AFC-5S
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2313, 1265, 890
Rint0.025
(sin θ/λ)max1)0.596
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.034, 0.092, 1.03
No. of reflections1265
No. of parameters141
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.10, 0.13

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1996), MSC/AFC Diffractometer Control Software, PROCESS in TEXSAN (Molecular Structure Corporation, 1997), SIR92 (Burla, 1989), LS in TEXSAN and SHELXL97 (Sheldrick, 1997), ORTEP-III (Farrugia, 1997), TEXSAN, SHELXL97 and PLATON (Spek, 2000).

Selected geometric parameters (Å, º) top
C2—C81.538 (3)C6—C121.526 (4)
C3—C91.533 (4)C6—C111.533 (4)
C7—C1—C2110.56 (19)C9—C3—C2114.0 (2)
C1—C2—C8110.9 (2)C12—C6—C1109.6 (2)
C8—C2—C3111.7 (2)C11—C6—C1110.33 (19)
C4—C3—C9111.8 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2···O3i0.821.912.712 (3)164
Symmetry code: (i) x, y1/2, z+3/2.
 

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