(2E,6E)-2,6-Bis(4-methyl­benzyl­idene)cyclo­hex-3-en-1-one

M Saeed Abaee; Werner Massa; Mohammad M Mojtahedi; A Wahid Mesbah

doi:10.1107/S1600536811055632

. 2012 Jan 11;68(Pt 2):o355. doi: 10.1107/S1600536811055632

(2E,6E)-2,6-Bis(4-methylbenzylidene)cyclohex-3-en-1-one

M Saeed Abaee ^a,^*, Werner Massa ^b,^*, Mohammad M Mojtahedi ^a, A Wahid Mesbah ^a

PMCID: PMC3275037 PMID: 22346982

Abstract

The title compound, C₂₂H₂₀O, shows an approximately planar cyclohexenone ring [maximum deviation = 0.069 (4) Å], with a disordered position of the C=C bond [ratio = 0.71 (2)/0.29 (2)]. The benzene rings of the 4-methylbenzylidene units, attached in the 2- and 6-positions to the cyclohexenone ring, are rotated in the same direction by 28.6 (4) and 22.4 (4)°, with respect to the mean plane of the cyclohexenone ring [fraction 0.71 (2); maximum deviation = 0.06 (3) Å]. In the crystal, molecules are packed in the manner of a distorted hexagonal rod packing with their long axes all aligned along [201]. A number of C—H⋯π interactions stablize the crystal structure.

Related literature

For background information to aldol condensation reactions in hetero- and homocyclic ketones, see: Abaee et al. (2007 ▶). For the crystal structure of the analogous compound with 4-methoxybenzylidene substituents in the 2- and 6- positions on the cyclohexenone ring, see: Abaee et al. (2007 ▶). For other similar substituted cyclohexenone structures, see: Shi et al. (2008 ▶); Guo et al. (2008 ▶).

Experimental

Crystal data

C₂₂H₂₀O
M _r = 300.38
Monoclinic,
a = 10.7108 (14) Å
b = 7.2772 (7) Å
c = 11.4690 (14) Å
β = 114.366 (14)°
V = 814.32 (17) Å³
Z = 2
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 193 K
0.50 × 0.24 × 0.15 mm

Data collection

Stoe IPDS image plate diffractometer
6110 measured reflections
1709 independent reflections
1219 reflections with I > 2σ(I)
R _int = 0.060

Refinement

R[F ² > 2σ(F ²)] = 0.035
wR(F ²) = 0.071
S = 0.98
1709 reflections
212 parameters
3 restraints
H-atom parameters constrained
Δρ_max = 0.17 e Å⁻³
Δρ_min = −0.15 e Å⁻³

Data collection: EXPOSE (Stoe & Cie, 1999 ▶); cell refinement: CELL (Stoe & Cie, 1999 ▶); data reduction: INTEGRATE (Stoe & Cie, 1999 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2011 ▶); software used to prepare material for publication: publCIF (Westrip 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536811055632/su2352sup1.cif

e-68-0o355-sup1.cif^{(21.1KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811055632/su2352Isup2.hkl

e-68-0o355-Isup2.hkl^{(82.4KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811055632/su2352Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

Cg1, Cg2 and Cg3 are the centroids of the C8–C11,C12a,C13, C1–C6 and C15–C20 rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3⋯Cg2ⁱ	0.95	2.78	3.538 (3)	137
C6—H6⋯Cg3ⁱⁱ	0.95	2.64	3.423 (3)	139
C16—H16⋯Cg3ⁱⁱⁱ	0.95	2.85	3.496 (3)	126
C13—H13b⋯Cg1ⁱⁱ	0.99	2.89	3.642 (6)	134

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

The authors would like to thank the Ministry of Science, Research and Technology of Iran for partial financial support of this work.

supplementary crystallographic information

Comment

In continuation of our studies on aldol condensation reactions in hetero- and homocyclic ketones (Abaee et al., 2007), we herein report on the synthesis and crystal structure of the title compound.

It crystallizes in the acentric space group P2₁ but the molecule shows pseudosymmetry m (C_s), with the mirror plane perpendicular to the main molecular plane. The C_s symmetry is broken by the central symmetry-less cyclohexenone ring, but a second orientation of the molecule generated by this mirror plane appears as an alternative disordered orientation in a ratio of 0.71 (2)/0.29 (2) (Fig. 1). A split atom model was refined [C12a/C12b: occupancies 0.71 (2)/(0.29 (2)] using restraints providing the same bond lengths for corresponding atom pairs, C11—C12a/C13—C12b and C11—C12b/C13—C12a, of 1.475 (5)/1.319 (5)Å. The strong anisotropy of the displacement parameters of the O atom may be associated to this disorder. In addition, one of the terminal methyl groups, C21, showed 1:1 disorder over two orientations [occupancy of 0.5 for each of the six H-atom postions].

A second pseudosymmetric mirror plane can be found in the main plane of the molecule, the realisation of which would lead to the centrosymmetric space group P2₁/m. The clear inclination of both benzene rings [II (C1-C6) and III (C15-C20)] by 28.6 (4) and 22.4 (4)°, respectively, to the cyclohexenone ring I (O1,C8-C11,C12a,C13) rules out this possibility. Benzene rings II and III are inclined to one another by 8.66 (13)°.

In the presence of only one O atom besides 22 C and 20 H atoms, the absolute structure could not be determined, and from the synthesis the formation of a racemate is expected. In an analogous compound, with 4-methoxybenzylidene substituents in the 2- and 6- positions on the cyclohexenone ring (Abaee et al., 2007), the benzene rings are rotated in opposite directions with respect to the central ring plane, while in the title compound the rotation is in the same direction (Fig. 1). In general the bond distances and angles are similar to those observed in analogues structures (Abaee et al., 2007; Shi et al., 2008; Guo et al., 2008).

In the crystal, molecules pack in the manner of a distorted hexagonal rod packing with their long axes all aligned along the [201] direction (Figs. 2 and 3). The intermolecular contacts are reinforced by C–H···π interactions (Table 1).

Experimental

A mixture of cyclohex-2-enone (193 µL, 2 mmol), 4-methylbenzaldehyde (471 µL, 4 mmol), triethylamine (1122 µL, 8 mmol), and ZnBr₂ (900 mg, 4 mmol) in 5 ml dry CH₂Cl₂ was stirred at room temperature under argon atmosphere for 10 h. The progress of the reaction was checked by TLC using a 1:8 mixture of EtOAc/hexane. At the end of the reaction, the mixture was diluted with CH₂Cl₂ and washed with brine. The organic layer was dried using Na₂SO₄ and concentrated under reduced pressure. The product obtained was isolated (540 mg, 90%) by column chromatography over silicagel using a 1:8 mixture of EtOAc/hexane. The solid product was recrystallized from EtOAc to give light-orange block-like crystals of the title compound.