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Acta Cryst. (2009). E65, o551    [ doi:10.1107/S1600536809004887 ]

cis-2,6-Dibenzylcyclohexanone

J. P. Culver, S. Parkin and P. A. Crooks

Abstract top

In the title compound, C20H22O, the molecule is a meso isomer with the two benzyl groups cis to each other. The central cyclohexanone ring adopts a chair conformation. The molecule lies on a noncrystallographic mirror plane and the dihedral angles of the benzyl groups with respect to the ketone moiety are 88.06 (6) and 89.07 (6)°.

Comment top

The stereochemistry of α,α'-dibenzylcycloalkanones (Irvine et al. 1972) and 2,6-dibenzylcyclohexanones (Corey et al. 1955), ammonium formate in organic synthesis: a versatile agent in catalytic hydrogen transfer reductions (Ram & Ehrenkaufer, 1988), and ammonium formate/palladium on carbon: A versatile system for catalytic hydrogen transfer reductions of carbon–carbon double bonds (Paryzek et al. 2003), are a few of the articles related to the study of our research. In the investigation of possible treatments for the abuse of methamphetamine, we have undertaken the design, synthesis, and structural analysis of a series of (cis)-2,6-dibenzylcyclohexan-1-one analogs and derivatives with variable substituents on the benzene ring. The primary goal of the X-ray analysis of the title compound was to confirm the cis stereochemistry of the benzyl substituents at C2 and C6 of the cyclohexanone ring, and to obtain detailed information on the structural conformation of the molecule for use in structure–activity relationship (SAR) studies.

The molecular structure of the title compound (Fig. 1) established the cis stereochemistry of the C2 and C6 benzyl substituents. The central cyclohexanone ring has a chair conformation. The molecule lies on a non-crystallographic mirror plane which passes through atoms O1, C1 and C4 and hence the torsion angles C1—C2—C14—C15 and C1—C6—C7—C8 are very similar (176.75 (16) and -176.89 (17)°, respectively). The dihedral angles of the benzyl groups with respect to the ketone moiety are 88.06 (6) and 89.07 (6)°.

Related literature top

For background literature, see: Irvine et al. (1972); Corey et al. (1955); Ram & Ehrenkaufer (1988); Paryzek et al. (2003).

Experimental top

A mixture of cyclohexanone (1.0 g, 10.2 mmol), benzaldehyde (2.3 g, 21.7 mmol), and potassium hydroxide (1.22 g, 21.7 mmol) was stirred in methanol (20 ml) at ambient temperature for 4 h. The yellow solid precipitate was collected by filtration, and washed with cold methanol to yield the crude 2,6-dibenzylidenecyclohexanone (2.6 g, 9.5 mmol). A portion of the 2,6-dibenzylidenecyclohexanone product (1.0 g, 3.65 mmol) was subjected to hydrogenation via addition of palladium (10% on carbon, 0.1 g) and an excess of ammonium formate (2.4 g, 38.1 mmol) and then brought to reflux in methanol (50 ml) for 4 h. After cooling to ambient temperature, the reaction mixture was filtered, and the solvent was evaporated under vacuum. Chloroform (5 ml) was added to precipitate the remaining excess of ammonium formate, which was then removed by filtration. The residue was subjected to flash chromatography (solvent system 50:1 hexane–ethyl acetate). The crude product was then evaporated to dryness and crystallized from methanol to yield (cis)-2,6-dibenzylcyclohexanone (0.48 g, 1.72 mmol) as a colorless crystalline solid, that was suitable for X-ray analysis.

Refinement top

All H atoms were located in difference Fourier syntheses, and refined using riding models with bond distances of 0.95 Å (Car—H), 0.99 Å (Csec—H), and 1.00 Å (Ctert—H). Isotropic H-atom displacement parameters were set to 1.2Ueq of the parent atom. Friedel opposites were merged for this structure because of the absence of any anomalous scattering with which to refine a physically meaningful value of the Flack parameter.

Computing details top

Data collection: COLLECT (Nonius, 1999); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and local procedures.

Figures top
[Figure 1] Fig. 1. A view of the molecule with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
cis-2,6-Dibenzylcyclohexanone top
Crystal data top
C20H22OF(000) = 600
Mr = 278.38Dx = 1.198 Mg m−3
Monoclinic, CcMo Kα radiation, λ = 0.71073 Å
Hall symbol: C -2ycCell parameters from 1926 reflections
a = 30.1194 (12) Åθ = 1.0–27.5°
b = 5.5650 (2) ŵ = 0.07 mm−1
c = 9.3048 (5) ÅT = 90 K
β = 98.276 (2)°Block cut from needle, colourless
V = 1543.38 (12) Å30.20 × 0.10 × 0.05 mm
Z = 4
Data collection top
Nonius KappaCCD
diffractometer		1750 independent reflections
Radiation source: fine-focus sealed tube1574 reflections with I > 2σ(I)
graphiteRint = 0.047
Detector resolution: 18 pixels mm-1θmax = 27.5°, θmin = 1.4°
ω scans at fixed χ = 55°h = −37→38
Absorption correction: multi-scan
(SCALEPACK; Otwinowski & Minor, 1997)		k = −6→7
Tmin = 0.986, Tmax = 0.996l = −12→11
12091 measured 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)] = 0.034H-atom parameters constrained
wR(F2) = 0.081 w = 1/[σ2(Fo2) + (0.0379P)2 + 0.4656P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max = 0.001
1750 reflectionsΔρmax = 0.18 e Å−3
191 parametersΔρmin = −0.14 e Å−3
2 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.013 (2)
Crystal data top
C20H22OV = 1543.38 (12) Å3
Mr = 278.38Z = 4
Monoclinic, CcMo Kα radiation
a = 30.1194 (12) ŵ = 0.07 mm−1
b = 5.5650 (2) ÅT = 90 K
c = 9.3048 (5) Å0.20 × 0.10 × 0.05 mm
β = 98.276 (2)°
Data collection top
Nonius KappaCCD
diffractometer		1750 independent reflections
Absorption correction: multi-scan
(SCALEPACK; Otwinowski & Minor, 1997)		1574 reflections with I > 2σ(I)
Tmin = 0.986, Tmax = 0.996Rint = 0.047
12091 measured reflectionsθmax = 27.5°
Refinement top
R[F2 > 2σ(F2)] = 0.034H-atom parameters constrained
wR(F2) = 0.081Δρmax = 0.18 e Å−3
S = 1.08Δρmin = −0.14 e Å−3
1750 reflectionsAbsolute structure: ?
191 parametersFlack parameter: ?
2 restraintsRogers parameter: ?
Special details top

Experimental. 1H NMR (CDCl3): δ 1.364 (dt, 2H), 1.47–1.63 (m, 1H), 1.73–1.82 (m, 1H), 2.01–2.09 (m, 2H), 2.424 (dd, 2H), 2.52–2.63 (m, 2H), 3.235 (dd, 2H), 7.13–7.30 (m, 10H); 13C NMR (CDCl3): δ 25.65 (C4), 35.15 (C3,C5), 35.78 (C7,C14), 53.15 (C2,C6), 126.04 (C11,C18), 128.39 (C9, C13, C16, C20), 129.28 (C10, C12, C17, C19), 140.68 (C8, C15), 212.80 (C1). m.p. 393–395 K (lit. m.p. 395 K)

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 > 2σ(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
O10.37985 (5)−0.0297 (3)0.40486 (14)0.0253 (3)
C10.38084 (7)0.1057 (3)0.50806 (19)0.0208 (4)
C20.33796 (7)0.1967 (4)0.5576 (2)0.0220 (4)
H20.33490.11410.65120.026*
C30.34065 (7)0.4687 (4)0.5882 (2)0.0241 (4)
H3A0.33970.55670.49540.029*
H3B0.31430.51860.63350.029*
C40.38336 (7)0.5351 (4)0.6884 (2)0.0242 (4)
H4A0.38410.71090.70490.029*
H4B0.38350.45500.78350.029*
C50.42475 (7)0.4597 (4)0.6235 (2)0.0235 (4)
H5A0.45200.50330.69130.028*
H5B0.42560.54810.53150.028*
C60.42510 (7)0.1872 (4)0.5934 (2)0.0224 (4)
H60.42860.10330.68940.027*
C70.46483 (7)0.1121 (4)0.5165 (2)0.0257 (5)
H7A0.4636−0.06380.50060.031*
H7B0.46180.19070.42010.031*
C80.51001 (7)0.1770 (4)0.6010 (2)0.0252 (4)
C90.53381 (7)0.3759 (4)0.5643 (2)0.0307 (5)
H90.52200.47120.48300.037*
C100.57469 (8)0.4375 (4)0.6453 (3)0.0354 (5)
H100.59060.57420.61920.042*
C110.59215 (7)0.2998 (5)0.7638 (3)0.0363 (6)
H110.62000.34190.81940.044*
C120.56876 (8)0.1000 (4)0.8012 (3)0.0343 (5)
H120.58050.00520.88280.041*
C130.52826 (7)0.0393 (4)0.7196 (2)0.0300 (5)
H130.5126−0.09900.74500.036*
C140.29661 (7)0.1293 (4)0.4477 (2)0.0260 (4)
H14A0.29900.20700.35340.031*
H14B0.2963−0.04680.43240.031*
C150.25298 (7)0.2043 (4)0.4972 (2)0.0255 (4)
C160.23059 (7)0.4124 (4)0.4440 (2)0.0306 (5)
H160.24200.50510.37180.037*
C170.19167 (8)0.4852 (4)0.4958 (3)0.0345 (5)
H170.17670.62770.45920.041*
C180.17461 (7)0.3511 (4)0.6005 (3)0.0346 (5)
H180.14830.40280.63690.042*
C190.19597 (7)0.1412 (4)0.6521 (2)0.0344 (5)
H190.18400.04690.72250.041*
C200.23492 (7)0.0694 (4)0.6003 (2)0.0294 (5)
H200.2495−0.07450.63600.035*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0313 (7)0.0223 (7)0.0228 (7)−0.0010 (6)0.0052 (6)−0.0033 (6)
C10.0280 (9)0.0163 (9)0.0187 (9)−0.0008 (8)0.0059 (7)0.0043 (7)
C20.0248 (9)0.0209 (10)0.0207 (9)−0.0020 (8)0.0041 (7)−0.0017 (8)
C30.0268 (10)0.0224 (10)0.0235 (10)0.0015 (8)0.0056 (8)−0.0015 (8)
C40.0305 (10)0.0212 (10)0.0213 (10)−0.0008 (8)0.0042 (8)−0.0017 (8)
C50.0266 (10)0.0222 (10)0.0221 (9)−0.0019 (8)0.0048 (8)−0.0012 (8)
C60.0249 (9)0.0210 (10)0.0220 (9)−0.0011 (8)0.0059 (7)0.0004 (7)
C70.0283 (10)0.0243 (11)0.0263 (10)−0.0011 (8)0.0095 (8)−0.0028 (8)
C80.0227 (10)0.0248 (11)0.0298 (10)−0.0009 (8)0.0093 (8)−0.0052 (8)
C90.0315 (11)0.0255 (11)0.0362 (12)0.0001 (9)0.0080 (9)0.0040 (9)
C100.0295 (11)0.0307 (13)0.0471 (14)−0.0058 (10)0.0093 (10)0.0023 (10)
C110.0248 (11)0.0434 (15)0.0409 (13)−0.0023 (10)0.0057 (9)−0.0023 (11)
C120.0287 (11)0.0402 (13)0.0348 (12)0.0030 (10)0.0068 (9)0.0053 (10)
C130.0268 (10)0.0296 (12)0.0356 (12)−0.0008 (9)0.0114 (9)0.0042 (10)
C140.0262 (10)0.0267 (11)0.0242 (10)−0.0008 (8)0.0003 (8)−0.0015 (8)
C150.0236 (10)0.0249 (11)0.0268 (10)−0.0014 (9)−0.0006 (8)−0.0034 (9)
C160.0280 (10)0.0286 (12)0.0343 (11)−0.0015 (9)0.0011 (9)0.0019 (9)
C170.0282 (11)0.0277 (12)0.0454 (14)0.0010 (9)−0.0024 (10)−0.0034 (10)
C180.0231 (10)0.0389 (13)0.0412 (12)−0.0023 (10)0.0026 (9)−0.0107 (11)
C190.0298 (11)0.0407 (13)0.0328 (11)−0.0069 (10)0.0049 (9)−0.0011 (10)
C200.0275 (11)0.0275 (11)0.0315 (11)−0.0024 (9)−0.0007 (9)0.0008 (9)
Geometric parameters (Å, °) top
O1—C11.217 (2)C9—H90.9500
C1—C21.519 (3)C10—C111.383 (3)
C1—C61.520 (3)C10—H100.9500
C2—C141.540 (3)C11—C121.387 (3)
C2—C31.541 (3)C11—H110.9500
C2—H21.0000C12—C131.383 (3)
C3—C41.521 (3)C12—H120.9500
C3—H3A0.9900C13—H130.9500
C3—H3B0.9900C14—C151.513 (3)
C4—C51.520 (3)C14—H14A0.9900
C4—H4A0.9900C14—H14B0.9900
C4—H4B0.9900C15—C201.389 (3)
C5—C61.542 (3)C15—C161.394 (3)
C5—H5A0.9900C16—C171.391 (3)
C5—H5B0.9900C16—H160.9500
C6—C71.538 (3)C17—C181.383 (4)
C6—H61.0000C17—H170.9500
C7—C81.514 (3)C18—C191.386 (3)
C7—H7A0.9900C18—H180.9500
C7—H7B0.9900C19—C201.390 (3)
C8—C91.388 (3)C19—H190.9500
C8—C131.390 (3)C20—H200.9500
C9—C101.391 (3)
O1—C1—C2121.35 (18)C13—C8—C7120.24 (19)
O1—C1—C6121.12 (17)C8—C9—C10120.8 (2)
C2—C1—C6117.52 (16)C8—C9—H9119.6
C1—C2—C14111.03 (16)C10—C9—H9119.6
C1—C2—C3111.05 (16)C11—C10—C9120.1 (2)
C14—C2—C3112.23 (17)C11—C10—H10120.0
C1—C2—H2107.4C9—C10—H10120.0
C14—C2—H2107.4C10—C11—C12119.7 (2)
C3—C2—H2107.4C10—C11—H11120.1
C4—C3—C2111.66 (17)C12—C11—H11120.1
C4—C3—H3A109.3C13—C12—C11119.8 (2)
C2—C3—H3A109.3C13—C12—H12120.1
C4—C3—H3B109.3C11—C12—H12120.1
C2—C3—H3B109.3C12—C13—C8121.2 (2)
H3A—C3—H3B107.9C12—C13—H13119.4
C5—C4—C3111.04 (15)C8—C13—H13119.4
C5—C4—H4A109.4C15—C14—C2112.67 (16)
C3—C4—H4A109.4C15—C14—H14A109.1
C5—C4—H4B109.4C2—C14—H14A109.1
C3—C4—H4B109.4C15—C14—H14B109.1
H4A—C4—H4B108.0C2—C14—H14B109.1
C4—C5—C6111.74 (16)H14A—C14—H14B107.8
C4—C5—H5A109.3C20—C15—C16118.5 (2)
C6—C5—H5A109.3C20—C15—C14120.31 (19)
C4—C5—H5B109.3C16—C15—C14121.21 (19)
C6—C5—H5B109.3C17—C16—C15120.5 (2)
H5A—C5—H5B107.9C17—C16—H16119.7
C1—C6—C7111.01 (16)C15—C16—H16119.7
C1—C6—C5111.09 (17)C18—C17—C16120.3 (2)
C7—C6—C5112.18 (16)C18—C17—H17119.9
C1—C6—H6107.4C16—C17—H17119.9
C7—C6—H6107.4C17—C18—C19119.9 (2)
C5—C6—H6107.4C17—C18—H18120.1
C8—C7—C6113.27 (16)C19—C18—H18120.1
C8—C7—H7A108.9C18—C19—C20119.7 (2)
C6—C7—H7A108.9C18—C19—H19120.2
C8—C7—H7B108.9C20—C19—H19120.2
C6—C7—H7B108.9C15—C20—C19121.2 (2)
H7A—C7—H7B107.7C15—C20—H20119.4
C9—C8—C13118.4 (2)C19—C20—H20119.4
C9—C8—C7121.35 (19)
O1—C1—C2—C14−9.2 (3)C7—C8—C9—C10178.18 (19)
C6—C1—C2—C14171.62 (17)C8—C9—C10—C110.1 (3)
O1—C1—C2—C3−134.82 (18)C9—C10—C11—C120.2 (4)
C6—C1—C2—C346.0 (2)C10—C11—C12—C130.2 (4)
C1—C2—C3—C4−50.9 (2)C11—C12—C13—C8−0.9 (3)
C14—C2—C3—C4−175.87 (16)C9—C8—C13—C121.1 (3)
C2—C3—C4—C558.5 (2)C7—C8—C13—C12−177.8 (2)
C3—C4—C5—C6−58.3 (2)C1—C2—C14—C15176.75 (16)
O1—C1—C6—C79.5 (3)C3—C2—C14—C15−58.3 (2)
C2—C1—C6—C7−171.33 (17)C2—C14—C15—C20−78.3 (2)
O1—C1—C6—C5135.05 (18)C2—C14—C15—C16100.0 (2)
C2—C1—C6—C5−45.8 (2)C20—C15—C16—C171.5 (3)
C4—C5—C6—C150.5 (2)C14—C15—C16—C17−176.9 (2)
C4—C5—C6—C7175.41 (16)C15—C16—C17—C18−0.3 (3)
C1—C6—C7—C8−176.89 (17)C16—C17—C18—C19−1.1 (3)
C5—C6—C7—C858.2 (2)C17—C18—C19—C201.2 (3)
C6—C7—C8—C9−101.5 (2)C16—C15—C20—C19−1.3 (3)
C6—C7—C8—C1377.4 (2)C14—C15—C20—C19177.04 (19)
C13—C8—C9—C10−0.7 (3)C18—C19—C20—C150.0 (3)
Acknowledgements top

This work was supported by NIDA (grant Nos. DA13519 and T32DA016176).

references
References top

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Ram, S. & Ehrenkaufer, R. E. (1988). Synthesis, 2, 91–95.

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