(R)-2-[1-(2,6-Dichloro-3,4,5-trimeth­oxy­benzo­yl)pyrrolidin-2-yl]-4,4,5,5-tetra­methyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide

Hai-Bo Wang; Zhuo Xiang; Lin-Lin Jing; Min Tian; Xiao-Li Sun

doi:10.1107/S1600536811010270

. 2011 Mar 26;67(Pt 4):o985–o986. doi: 10.1107/S1600536811010270

(R)-2-[1-(2,6-Dichloro-3,4,5-trimethoxybenzoyl)pyrrolidin-2-yl]-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide

Hai-Bo Wang ^a, Zhuo Xiang ^a, Lin-Lin Jing ^b, Min Tian ^a, Xiao-Li Sun ^a,^*

PMCID: PMC3099877 PMID: 21754243

Abstract

In the title compound, C₂₁H₂₈Cl₂N₃O₆, the nitronyl nitroxide ring displays a half-chair conformation, whereas the pyrrolidine ring has an envelope conformation. These two rings are twisted to each other with N—C—C—N torsion angles around the connecting C—C bond of 48.9 (6) and −127.0 (5)°. The benzene ring is nearly perpendicular to the pyrrolidine ring, with torsion angles around the connecting C—C bond of 86.3 (6) and −97.7 (6)°. The crystal structure is stabilized by C—H⋯O and C—H⋯π hydrogen bonds, which build up a three-dimensional network.

Related literature

For the chemical and physical properties of nitronyl nitroxides, see: Minguet et al. (2001 ▶); Osiecki & Ullman (1968 ▶); Shemsi et al. (2007 ▶); Wu et al. (2006 ▶). For related structures, see: Shimono et al. (2004 ▶); Minguet et al. (2001 ▶); Tian et al. (2011 ▶). For puckering parameters, see Cremer & Pople (1975 ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶).

Experimental

Crystal data

C₂₁H₂₈Cl₂N₃O₆
M _r = 489.36
Orthorhombic,
a = 10.975 (2) Å
b = 12.255 (3) Å
c = 17.741 (4) Å
V = 2386.2 (8) Å³
Z = 4
Mo Kα radiation
μ = 0.31 mm⁻¹
T = 296 K
0.38 × 0.27 × 0.16 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2007 ▶) T _min = 0.892, T _max = 0.952
12018 measured reflections
4252 independent reflections
2217 reflections with I > 2σ(I)
R _int = 0.067

Refinement

R[F ² > 2σ(F ²)] = 0.053
wR(F ²) = 0.131
S = 1.02
4252 reflections
297 parameters
H-atom parameters constrained
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.16 e Å⁻³
Absolute structure: Flack (1983 ▶), 1834 Friedel pairs
Flack parameter: 0.01 (10)

Data collection: APEX2 (Bruker, 2007 ▶); cell refinement: SAINT (Bruker, 2007 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEPIII (Burnett & Johnson, 1996 ▶) and ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶) and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811010270/dn2666sup1.cif

e-67-0o985-sup1.cif^{(24.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811010270/dn2666Isup2.hkl

e-67-0o985-Isup2.hkl^{(208.4KB, hkl)}

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

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

Cg3 is the centroid of the C13–C18 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C6—H6B⋯O3ⁱ	0.96	2.54	3.498 (8)	173
C11—H11A⋯O1ⁱⁱ	0.97	2.36	3.281 (6)	159
C21—H21B⋯O2ⁱⁱⁱ	0.96	2.44	3.403 (6)	178
C4—H4A⋯Cg3ⁱ	0.96	2.86	3.619 (7)	136

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

Acknowledgments

We thank the Natural Science Foundation of China (grant Nos. 81001398, 30901883, 20802091, 20802092) for financial support.

supplementary crystallographic information

Comment

Nitronyl nitroxides, stable organic radicals, synthesized more than 30 years ago (Osiecki et al., 1968), have received considerable attention recently because of their capability of magnetism, anticancer, antiradiation and antioxidation in biological chemistry and magnetic material fields (Shemsi et al., 2007; Wu et al., 2006). Chiral nitroxides are well chosen as potential precursors of chiralmolecule-based magnets. However, chiral nitronyl nitroxide radicals with the chiral centers sitting very close to the oxyl group are relatively few in the literature (Minguet et al., 2001; Shimono et al., 2004; Tian et al., 2011).

In the title compound, the nitronyl nitroxide ring displays half-chair conformation with puckering parameters, Q2 = 0.096 (5)Å and φ = 272 (3)° (Cremer & Pople, 1975) whereas the pyrrolidine ring has an envelope conformation with puckering parameters Q(2)= 0.393 (6) Å and φ = 104.3 (7)°. The N3—C12—C13—C14, -97.7 (6)°, and N3—C12—C13—C18, 86.3 (6)°, torsion angles the involving the ketone bridging group show that the phenyl and the pyrrolidine rings are nearly perpendicular (Fig. 1). The bond distances and bond angles within the molecule agree with values reported in the Cambridge Structural Database (Allen, 2002).

Intermolecular C—H···O and C—H···π hydrogen bonds stabilize the packing building up a three dimensionnal network (Table 1).

Experimental

2,6-dichloro-3,4,5-trimethoxybenzoylchloride (2.98 g, 10.0 mmol), Et₃N (3.1 ml) were added to in dry CH₂Cl₂ with vigorous stirring in an ice bath. To this mixture, a solution of prolinol (1.0 g, 10 mmol) in dry CH₂Cl₂was added dropwise over a period of 20 min. The mixture was warmed to room temperature and stirred for 2 h. Then the reaction mixture was treated with water and extracted with CH₂Cl₂. The organic layer wasdried over anhydrous MgSO₄ and concentrated. The crude product was purified by column chromatography on silica gel using ethyl acetate/petroleum ether (3:1) as eluant, giving a colorless oil product (3.1 g, 83.8%). To a reaction mixture of this product (3.61 g, 10 mmol), TEMPO (0.025 g, 0.16 mmol) and trichloroisocyanuric acid (TCCA, 3.7 g, 16 mmol), CH₂Cl₂ was added. Then the mixture was stirred for 20 min and filtered on Celite. The precipitate was purified by column chromatography on silica gel using ethyl acetate/petroleumether/triethylamine (2:1:0.1) as eluant, giving the product 1-(2,6-dichloro-3,4,5-trimethoxybenzoyl)pyrrolidine-2-carbaldehyde (3.10 g, 85.0%). 2,3-Dimethyl-2,3-bis(hydroxylamino) butane (0.74 g, 10.0 mmol) and 1-(2,6-dichloro-3,4,5- trime thoxybenzoyl) pyrrolidine-2-carbaldehyde (1.81 g, 5.0 mmol) were dissolved in methanol. The reaction was stirred for 10 h at reflux temperature, then cooled to room temperature and filtered. The cake was suspended in CH₂Cl₂ (150.0 ml) and cooled at ice bath for 10 min. Then the reaction mixture was added to an aqueous solution of NaIO₄ stirring for 15 min. The aqueous phase was extracted with CH₂Cl₂ and the organic layer was combined and dried over MgSO₄. Then the solvent wasremoved to give a amaranthine residue which was purified by a flash columnchromatography with the elution of n-hexane/ethyl acetate (1:1) to yield thetitle compound (I) as a dark amaranthine powder. Single crystals of compound (I) were obtained from the 1/1 mixed solution of n-heptane and dichloromethane.