(1S,3R,8R)-2,2-Dibromo-3,7,7,10-tetra­methyltricyclo­[6.4.0.01,3]dodec-9-en-11-one

Oukhrib, A.; Benharref, A.; Saadi, M.; El Ammari, L.; Berraho, M.

doi:10.1107/S1600536812046089

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 68| Part 12| December 2012| Pages o3341-o3342

doi:10.1107/S1600536812046089

Open

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(1S,3R,8R)-2,2-Dibromo-3,7,7,10-tetramethyltricyclo[6.4.0.0^1,3]dodec-9-en-11-one

Abdelouahd Oukhrib,^a ^* Ahmed Benharref,^a Mohamed Saadi,^b Lahcen El Ammari ^b and Moha Berraho ^a

^aLaboratoire de Chimie des Substances Naturelles, "Unité Associé au CNRST (URAC16)", Faculté des Sciences Semlalia, BP 2390 Bd My Abdellah, 40000 Marrakech, Morocco, and ^bLaboratoire de Chimie du Solide Appliquée, Faculté des Sciences, Avenue Ibn Battouta, BP 1014 Rabat, Morocco
^*Correspondence e-mail: berraho@uca.ma

(Received 29 October 2012; accepted 7 November 2012; online 14 November 2012)

The title compound, C₁₆H₂₂Br₂O, was synthesized from β-himachalene (3,5,5,9-tetramethyl-2,4a,5,6,7,8-hexahydro-1H-benzocycloheptene), which was isolated from the essential oil of the Atlas cedar (Cedrus Atlantica). The molecule is built up from fused six- and seven-membered rings and an additional three-membered ring from the reaction of himachalene with dibromocarbene. The six-membered ring has an envelope conformation, with the C atom belonging to the three-membered ring forming the flap, whereas the seven-membered ring displays a screw-boat conformation; the dihedral angle between the rings (all atoms) is 60.92 (16)°.

Related literature

For the isolation of β-himachalene, see: Joseph & Dev (1968 ); Plattier & Teiseire (1974 ). For the reactivity of this sesquiterpene, see: Lassaba et al. (1997 ); Chekroun et al. (2000 ); El Jamili et al. (2002 ); Sbai et al. (2002 ); Dakir et al. (2004 ). For its biological activity, see: Daoubi et al. (2004 ). For conformational analysis, see: Cremer & Pople (1975 ).

Experimental

Crystal data

C₁₆H₂₂Br₂O
M_r = 390.16
Orthorhombic, P 2₁ 2₁ 2₁
a = 6.7369 (1) Å
b = 14.7635 (3) Å
c = 16.3543 (3) Å
V = 1626.60 (5) Å³
Z = 4
Mo Kα radiation
μ = 4.98 mm⁻¹
T = 298 K
0.80 × 0.65 × 0.25 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2003 ) T_min = 0.259, T_max = 0.746
11891 measured reflections
3330 independent reflections
2939 reflections with I > 2σ(I)
R_int = 0.028

Refinement

R[F² > 2σ(F²)] = 0.030
wR(F²) = 0.074
S = 1.06
3330 reflections
176 parameters
H-atom parameters constrained
Δρ_max = 0.68 e Å⁻³
Δρ_min = −0.37 e Å⁻³
Absolute structure: Flack (1983), 1397 Friedel pairs
Flack parameter: 0.021 (12)

Data collection: APEX2 (Bruker, 2009 ); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012 ); software used to prepare material for publication: WinGX (Farrugia, 2012).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536812046089/go2074sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812046089/go2074Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536812046089/go2074Isup3.cml

checkCIF report

Comment top

The essential oil of the Atlas cedar (Cedrus atlantica) consist mainly (50%) of a bicyclic hydrocarbon called β-himachalene (Plattier & Teiseire(1974); Joseph & Dev (1968)). The reactivity of this sesquiterpene and its derivatives has been studied extensively by our team in order to prepare new products having biological proprieties. (Lassaba et al., 1997; Chekroun et al., 2000; El Jamili et al., 2002; Sbai et al., 2002; Dakir et al., 2004). Indeed, these compounds were tested, using the food poisoning technique, for their potential antifungal activity against the phytopathogen Botrytis cinerea (Daoubi et al., 2004). In a previous work (El Jamili et al., 2002), we have prepared, from β-himachalene, the (1S,3R,8R)-2,2-dibromo- 3,7,7,10- tetramethyltricyclo [6.4.0.01,3] dodec-9-ene, which is treated with N-bromosuccinimide and gave the title compound. The structure of this new product was determined by its single-crystal X-ray structure. The molecule is built up from two fused six-and seven- membered rings and an additional three-membered ring from the reaction with the carbene (Fig.1). The six-membered ring has an envelope conformation, as indicated by the total puckering amplitude QT = 0.433 (3) Å and spherical polar angle θ= 123.1 (4)° with ϕ = 181.6 (5)°, whereas the seven-membered ring display a screw boat conformation with QT = 1.1208 (4) Å, θ = 88.14 (2)°, ϕ2 = -49.94 (2)° and ϕ3 = -93.26 (5)° (Cremer & Pople, 1975). Owing to the presence of Br atoms, the absolute configuration could be fully confirmed, by refining the Flack parameter (Flack & Bernardinelli (2000)) as C1(S), C3(R) and C8(R).

Related literature top

For the isolation of β-himachalene, see: Joseph & Dev (1968); Plattier & Teiseire (1974). For the reactivity of this sesquiterpene, see: Lassaba et al. (1997); Chekroun et al. (2000); El Jamili et al. (2002); Sbai et al. (2002); Dakir et al. (2004). For its biological activity, see: Daoubi et al. (2004). For conformational analysis, see: Cremer & Pople (1975).

Experimental top

In a reactor containing a solution of (1S, 3R, 8R)-2,2-dibromo- 3,7,7,10 tetramethyltricyclo [6.4.0.01,3] dodec-9-ene (1 g, 2,6 mmol) in 50 ml of tetrahydrofuran and water (THF/H2O) (4:1) cooled to 273 K and kept in the dark, was added in small portions 1 g (5,6 mmol) of N-bromosccinimide. The reaction mixture was left stirring for 1 h, after which 20 ml of a saturated solution of NaHCO₃ was added. Subsequently, the extraction was performed three times with diethyl ether (3 x 20 ml). The organic extracts were dried over Na₂S_O4, filtered, concentrated, and chromatographed. The title compound was obtained with a yield of 80% and was recrystallized in n-pentane.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures top

Fig. 1. : Molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability. level. H atoms are represented as small spheres of arbitrary radii.

(1S,3R,8R)-2,2-Dibromo-3,7,7,10- tetramethyltricyclo[6.4.0.0^1,3]dodec-9-en-11-one top

Crystal data top

C₁₆H₂₂Br₂O	F(000) = 784
M_r = 390.16	D_x = 1.593 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 11891 reflections
a = 6.7369 (1) Å	θ = 2.8–26.4°
b = 14.7635 (3) Å	µ = 4.98 mm⁻¹
c = 16.3543 (3) Å	T = 298 K
V = 1626.60 (5) Å³	Prism, colourless
Z = 4	0.80 × 0.65 × 0.25 mm

Data collection top

Bruker APEXII CCD diffractometer	3330 independent reflections
Radiation source: fine-focus sealed tube	2939 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.028
ω and ϕ scans	θ_max = 26.4°, θ_min = 2.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −7→8
T_min = 0.259, T_max = 0.746	k = −18→18
11891 measured reflections	l = −20→20

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.030	H-atom parameters constrained
wR(F²) = 0.074	w = 1/[σ²(F_o²) + (0.034P)² + 0.368P] where P = (F_o² + 2F_c²)/3
S = 1.06	(Δ/σ)_max = 0.001
3330 reflections	Δρ_max = 0.68 e Å⁻³
176 parameters	Δρ_min = −0.37 e Å⁻³
0 restraints	Absolute structure: Flack (1983), 1397 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.021 (12)

Crystal data top

C₁₆H₂₂Br₂O	V = 1626.60 (5) Å³
M_r = 390.16	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 6.7369 (1) Å	µ = 4.98 mm⁻¹
b = 14.7635 (3) Å	T = 298 K
c = 16.3543 (3) Å	0.80 × 0.65 × 0.25 mm

Data collection top

Bruker APEXII CCD diffractometer	3330 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	2939 reflections with I > 2σ(I)
T_min = 0.259, T_max = 0.746	R_int = 0.028
11891 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.030	H-atom parameters constrained
wR(F²) = 0.074	Δρ_max = 0.68 e Å⁻³
S = 1.06	Δρ_min = −0.37 e Å⁻³
3330 reflections	Absolute structure: Flack (1983), 1397 Friedel pairs
176 parameters	Absolute structure parameter: 0.021 (12)
0 restraints

Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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

	x	y	z	U_iso*/U_eq
C1	0.7886 (4)	0.8949 (2)	0.72986 (18)	0.0345 (7)
C2	0.7652 (4)	0.8664 (2)	0.8186 (2)	0.0381 (7)
C3	0.8277 (5)	0.9620 (2)	0.79993 (18)	0.0381 (7)
C4	0.6771 (5)	1.0379 (2)	0.8104 (2)	0.0458 (8)
H4A	0.7011	1.0681	0.8621	0.055*
H4B	0.5449	1.0120	0.8124	0.055*
C5	0.6854 (6)	1.1078 (2)	0.7417 (2)	0.0545 (9)
H5A	0.5580	1.1383	0.7392	0.065*
H5B	0.7842	1.1529	0.7560	0.065*
C6	0.7335 (7)	1.0720 (3)	0.6570 (3)	0.0635 (11)
H6A	0.8704	1.0516	0.6578	0.076*
H6B	0.7270	1.1228	0.6195	0.076*
C7	0.6078 (5)	0.9950 (2)	0.62020 (19)	0.0411 (7)
C8	0.6031 (4)	0.9087 (2)	0.67808 (18)	0.0353 (7)
H8	0.4927	0.9177	0.7163	0.042*
C9	0.5589 (4)	0.8232 (2)	0.63150 (19)	0.0417 (7)
H9	0.4286	0.8142	0.6145	0.050*
C10	0.6912 (5)	0.7587 (2)	0.61230 (18)	0.0391 (7)
C11	0.9012 (4)	0.7704 (2)	0.63421 (19)	0.0399 (7)
C12	0.9602 (4)	0.8536 (2)	0.68244 (19)	0.0420 (7)
H12A	1.0130	0.8986	0.6451	0.050*
H12B	1.0649	0.8374	0.7204	0.050*
C13	1.0396 (5)	0.9900 (3)	0.8188 (2)	0.0537 (9)
H13A	1.1285	0.9418	0.8042	0.081*
H13B	1.0520	1.0026	0.8762	0.081*
H13C	1.0724	1.0434	0.7881	0.081*
C14	0.3936 (7)	1.0248 (3)	0.6061 (3)	0.0832 (15)
H14A	0.3917	1.0760	0.5699	0.125*
H14B	0.3345	1.0413	0.6574	0.125*
H14C	0.3200	0.9759	0.5821	0.125*
C15	0.6966 (8)	0.9745 (3)	0.5362 (3)	0.0758 (13)
H15A	0.8355	0.9615	0.5419	0.114*
H15B	0.6796	1.0261	0.5011	0.114*
H15C	0.6304	0.9231	0.5128	0.114*
C16	0.6372 (7)	0.6755 (2)	0.5647 (2)	0.0584 (10)
H16A	0.4981	0.6768	0.5520	0.088*
H16B	0.6662	0.6226	0.5967	0.088*
H16C	0.7126	0.6738	0.5149	0.088*
Br1	0.50492 (5)	0.83972 (3)	0.86363 (2)	0.05453 (12)
Br2	0.94858 (5)	0.78265 (3)	0.86827 (3)	0.06271 (13)
O	1.0289 (4)	0.71769 (17)	0.61207 (15)	0.0604 (6)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0291 (15)	0.0354 (17)	0.0390 (16)	0.0008 (13)	0.0031 (12)	−0.0040 (14)
C2	0.0293 (14)	0.0415 (18)	0.0434 (17)	0.0048 (12)	0.0006 (12)	−0.0004 (15)
C3	0.0355 (15)	0.0398 (17)	0.0391 (16)	−0.0008 (14)	0.0006 (13)	−0.0075 (14)
C4	0.0517 (19)	0.0401 (18)	0.0456 (18)	0.0045 (16)	0.0033 (15)	−0.0135 (16)
C5	0.070 (2)	0.0361 (19)	0.057 (2)	0.0011 (18)	−0.0057 (19)	−0.0068 (18)
C6	0.078 (3)	0.045 (2)	0.067 (3)	−0.006 (2)	−0.003 (2)	0.002 (2)
C7	0.0458 (16)	0.0382 (16)	0.0393 (17)	−0.0022 (14)	−0.0020 (14)	0.0005 (15)
C8	0.0297 (14)	0.0371 (17)	0.0393 (15)	−0.0010 (13)	0.0013 (12)	−0.0028 (14)
C9	0.0397 (14)	0.0435 (17)	0.0419 (16)	−0.0081 (13)	−0.0024 (15)	−0.0010 (16)
C10	0.0522 (18)	0.0337 (16)	0.0316 (15)	−0.0068 (14)	0.0025 (13)	0.0004 (13)
C11	0.0483 (16)	0.0338 (16)	0.0376 (15)	0.0066 (14)	0.0120 (15)	0.0031 (15)
C12	0.0323 (15)	0.0471 (18)	0.0465 (17)	0.0037 (14)	0.0048 (13)	−0.0093 (15)
C13	0.0470 (19)	0.058 (2)	0.0559 (19)	−0.0065 (18)	−0.0019 (16)	−0.0152 (18)
C14	0.069 (3)	0.079 (3)	0.102 (4)	0.008 (2)	−0.009 (2)	0.042 (3)
C15	0.095 (3)	0.072 (3)	0.061 (2)	−0.010 (3)	0.012 (2)	0.009 (2)
C16	0.086 (3)	0.037 (2)	0.052 (2)	−0.009 (2)	−0.0035 (19)	0.0003 (17)
Br1	0.04425 (17)	0.0613 (2)	0.0581 (2)	−0.00202 (17)	0.01213 (17)	0.00965 (18)
Br2	0.0559 (2)	0.0613 (2)	0.0710 (2)	0.01579 (18)	−0.00973 (19)	0.0117 (2)
O	0.0663 (16)	0.0493 (14)	0.0657 (14)	0.0148 (14)	0.0091 (13)	−0.0101 (12)

Geometric parameters (Å, º) top

C1—C2	1.518 (4)	C8—H8	0.9800
C1—C12	1.520 (4)	C9—C10	1.341 (5)
C1—C8	1.524 (4)	C9—H9	0.9300
C1—C3	1.537 (4)	C10—C11	1.470 (4)
C2—C3	1.503 (5)	C10—C16	1.499 (5)
C2—Br2	1.928 (3)	C11—O	1.216 (4)
C2—Br1	1.943 (3)	C11—C12	1.512 (5)
C3—C13	1.518 (4)	C12—H12A	0.9700
C3—C4	1.522 (5)	C12—H12B	0.9700
C4—C5	1.526 (5)	C13—H13A	0.9600
C4—H4A	0.9700	C13—H13B	0.9600
C4—H4B	0.9700	C13—H13C	0.9600
C5—C6	1.517 (5)	C14—H14A	0.9600
C5—H5A	0.9700	C14—H14B	0.9600
C5—H5B	0.9700	C14—H14C	0.9600
C6—C7	1.541 (5)	C15—H15A	0.9600
C6—H6A	0.9700	C15—H15B	0.9600
C6—H6B	0.9700	C15—H15C	0.9600
C7—C14	1.526 (5)	C16—H16A	0.9600
C7—C15	1.529 (5)	C16—H16B	0.9600
C7—C8	1.587 (5)	C16—H16C	0.9600
C8—C9	1.505 (4)

C2—C1—C12	117.1 (3)	C1—C8—C7	115.0 (2)
C2—C1—C8	118.9 (2)	C9—C8—H8	106.6
C12—C1—C8	113.2 (2)	C1—C8—H8	106.6
C2—C1—C3	58.9 (2)	C7—C8—H8	106.6
C12—C1—C3	120.6 (3)	C10—C9—C8	125.7 (3)
C8—C1—C3	117.9 (3)	C10—C9—H9	117.2
C3—C2—C1	61.1 (2)	C8—C9—H9	117.2
C3—C2—Br2	120.5 (2)	C9—C10—C11	119.9 (3)
C1—C2—Br2	120.9 (2)	C9—C10—C16	122.8 (3)
C3—C2—Br1	121.3 (2)	C11—C10—C16	117.2 (3)
C1—C2—Br1	120.8 (2)	O—C11—C10	122.2 (3)
Br2—C2—Br1	106.75 (16)	O—C11—C12	119.3 (3)
C2—C3—C13	118.5 (3)	C10—C11—C12	118.4 (3)
C2—C3—C4	118.8 (3)	C11—C12—C1	113.1 (3)
C13—C3—C4	113.8 (3)	C11—C12—H12A	109.0
C2—C3—C1	59.9 (2)	C1—C12—H12A	109.0
C13—C3—C1	119.3 (3)	C11—C12—H12B	109.0
C4—C3—C1	116.4 (3)	C1—C12—H12B	109.0
C3—C4—C5	113.0 (3)	H12A—C12—H12B	107.8
C3—C4—H4A	109.0	C3—C13—H13A	109.5
C5—C4—H4A	109.0	C3—C13—H13B	109.5
C3—C4—H4B	109.0	H13A—C13—H13B	109.5
C5—C4—H4B	109.0	C3—C13—H13C	109.5
H4A—C4—H4B	107.8	H13A—C13—H13C	109.5
C6—C5—C4	116.4 (3)	H13B—C13—H13C	109.5
C6—C5—H5A	108.2	C7—C14—H14A	109.5
C4—C5—H5A	108.2	C7—C14—H14B	109.5
C6—C5—H5B	108.2	H14A—C14—H14B	109.5
C4—C5—H5B	108.2	C7—C14—H14C	109.5
H5A—C5—H5B	107.4	H14A—C14—H14C	109.5
C5—C6—C7	119.8 (4)	H14B—C14—H14C	109.5
C5—C6—H6A	107.4	C7—C15—H15A	109.5
C7—C6—H6A	107.4	C7—C15—H15B	109.5
C5—C6—H6B	107.4	H15A—C15—H15B	109.5
C7—C6—H6B	107.4	C7—C15—H15C	109.5
H6A—C6—H6B	106.9	H15A—C15—H15C	109.5
C14—C7—C15	106.9 (3)	H15B—C15—H15C	109.5
C14—C7—C6	111.5 (3)	C10—C16—H16A	109.5
C15—C7—C6	106.4 (3)	C10—C16—H16B	109.5
C14—C7—C8	107.6 (3)	H16A—C16—H16B	109.5
C15—C7—C8	112.7 (3)	C10—C16—H16C	109.5
C6—C7—C8	111.7 (3)	H16A—C16—H16C	109.5
C9—C8—C1	109.3 (3)	H16B—C16—H16C	109.5
C9—C8—C7	112.1 (2)

Experimental details

Crystal data
Chemical formula	C₁₆H₂₂Br₂O
M_r	390.16
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	298
a, b, c (Å)	6.7369 (1), 14.7635 (3), 16.3543 (3)
V (Å³)	1626.60 (5)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	4.98
Crystal size (mm)	0.80 × 0.65 × 0.25

Data collection
Diffractometer	Bruker APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2003)
T_min, T_max	0.259, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	11891, 3330, 2939
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.030, 0.074, 1.06
No. of reflections	3330
No. of parameters	176
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.68, −0.37
Absolute structure	Flack (1983), 1397 Friedel pairs
Absolute structure parameter	0.021 (12)

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012), WinGX (Farrugia, 2012).

Acknowledgements

The authors thank the Unit of Support for Technical and Scientific Research (UATRS, CNRST) for the X-ray measurements.

References

Bruker (2009). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Chekroun, A., Jarid, A., Benharref, A. & Boutalib, A. (2000). J. Org. Chem. 65, 4431–4434. Web of Science CrossRef PubMed CAS Google Scholar
Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354–1358. CrossRef CAS Web of Science Google Scholar
Dakir, M., Auhmani, A., Ait Itto, M. Y., Mazoir, N., Akssira, M., Pierrot, M. & Benharref, A. (2004). Synth. Commun. 34, 2001–2008. Web of Science CrossRef CAS Google Scholar
Daoubi, M., Duran-Patron, R., Hmamouchi, M., Hernandez-Galan, R., Benharref, A. & Isidro, G. C. (2004). Pest Manag. Sci. 60, 927–932. Web of Science CrossRef PubMed CAS Google Scholar
El Jamili, H., Auhmani, A., Dakir, M., Lassaba, E., Benharref, A., Pierrot, M., Chiaroni, A. & Riche, C. (2002). Tetrahedron Lett. 43, 6645–6648. CAS Google Scholar
Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Web of Science CrossRef CAS IUCr Journals Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Joseph, T. C. & Dev, S. (1968). Tetrahedron, 24, 3841–3859. CrossRef CAS Web of Science Google Scholar
Lassaba, E., Chekroun, A., Benharref, A., Chiaroni, A., Riche, C. & Lavergne, J.-P. (1997). Bull. Soc. Chim. Belg. 106, 281–288. CAS Google Scholar
Plattier, M. & Teiseire, P. (1974). Recherche, 19, 131–144. CAS Google Scholar
Sbai, F., Dakir, M., Auhmani, A., El Jamili, H., Akssira, M., Benharref, A., Kenz, A. & Pierrot, M. (2002). Acta Cryst. C58, o518–o520. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Sheldrick, G. M. (2003). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar

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