4-[2-(Benzyl­amino)­phen­yl]-2,6-dimethyl­quinoline N-oxide

Mario Geffe; Dieter Schollmeyer; Heiner Detert

doi:10.1107/S1600536812011002

. 2012 Mar 17;68(Pt 4):o1106. doi: 10.1107/S1600536812011002

4-[2-(Benzylamino)phenyl]-2,6-dimethylquinoline N-oxide

Mario Geffe ^a, Dieter Schollmeyer ^a, Heiner Detert ^a,^*

PMCID: PMC3344055 PMID: 22589964

Abstract

The title compound, C₂₄H₂₂N₂O, was obtained in a two-step procedure from the corresponding 4-(2-iodophenyl)quinoline. The quinoline system is approximately planar [maximum deviation from the least-squares plane = 0.021 (2) Å]. The planes of the quinoline system and the phenyl ring subtend a dihedral angle of 78.08 (8)°. In the crystal, pairs of molecules are connected via a center of symmetry and linked by a pair of angular N—H⋯O hydrogen bond. These dimers form columns oriented along the c axis.

Related literature

For aminations of iodolium salts, see: Letessier et al. (2011a ▶,b ▶), Letessier & Detert (2012 ▶). For quinoline N-oxides, see: Moreno-Fuquen et al. (2007 ▶); Ivashevskaja et al. (2002 ▶); Fahlquist et al. (2006 ▶). For heteroanalogous carbazoles, see: Dassonneville et al. (2010 ▶, 2011 ▶); Nissen & Detert (2011 ▶). For Buchwald-Hartwig amination, see: Hartwig (1999 ▶); Muci & Buchwald (2002 ▶). For twist of o-substituted biaryls, see: Miao et al. (2009 ▶); Moschel et al. (2011 ▶).

Experimental

Crystal data

C₂₄H₂₂N₂O
M _r = 354.44
Monoclinic,
a = 10.1656 (3) Å
b = 14.1135 (5) Å
c = 12.9372 (4) Å
β = 91.547 (3)°
V = 1855.46 (11) Å³
Z = 4
Cu Kα radiation
μ = 0.61 mm⁻¹
T = 193 K
0.26 × 0.18 × 0.18 mm

Data collection

Stoe IPDS 2T diffractometer
18005 measured reflections
3120 independent reflections
2803 reflections with I > 2σ(I)
R _int = 0.034

Refinement

R[F ² > 2σ(F ²)] = 0.050
wR(F ²) = 0.154
S = 1.10
3120 reflections
246 parameters
H-atom parameters constrained
Δρ_max = 0.17 e Å⁻³
Δρ_min = −0.18 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2011) ▶; cell refinement: X-AREA ▶; data reduction: X-RED (Stoe & Cie, 2011) ▶; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: PLATON (Spek, 2009 ▶); software used to prepare material for publication: PLATON.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812011002/bt5844sup1.cif

e-68-o1106-sup1.cif^{(29.7KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812011002/bt5844Isup2.hkl

e-68-o1106-Isup2.hkl^{(153.1KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536812011002/bt5844Isup3.cml

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

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

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N7—H7⋯O24ⁱ	0.96	2.03	2.7852 (17)	134

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Symmetry code: (i) Inline graphic .

Acknowledgments

The authors are grateful to Heinz Kolshorn for the NMR spectra and invaluable discussions.

supplementary crystallographic information

Comment

As part of a larger project on the synthesis of heteroanalogous carbazoles (Dassonneville et al. (2011), Dassonneville et al. (2010); Nissen & Detert (2011) iodolium salts became interesting as intermediates. Their twofold Buchwald-Hartwig amination with primary amines results in the formation of the pyrrole ring leading to carbazoles (Letessier et al. (2011a)) or carbolines (Letessier et al. (2011b), Letessier & Detert (2012)). The attempted formation of a benzo-quinolino-annulated iodolium salt via oxidation of the 4-(2-iodophenyl)quinoline and electrophilic ring closure failed. A mixture of two compounds, probably the iodosophenyl-quinoline and the iodophenyl-quinoline-N-oxide was obtained instead. Upon standing in chloroform solution, the former slowly isomerizes to the latter compound. Buchwald-Hartwig amination of the inseparable mixture with benzyl amine and Pd₂(dba)₃/Xantphos as catalytic system results in the formation of the title compound (ca 35%).

The title compound crystallizes as a centrosymmetric dimer stabilized by hydrogen bonding from the amino group to the N-oxide. The dimers are arranged in independent columns along the c axis. The bonds N7—H7 (0.9629 Å) and H7—O24 (2.03 Å) open an angle of 134°.

The quinoline framework is essentially planar with a maximal deviation of 0.021 (2) Å at C17 from the mean square plane. The dihedral angle between the mean planes of the quinoline and the adjacent phenyl ring is 64.61 (6)° and the mean planes of the phenyl rings open an angle of 78.08 (8)°. The amino group is coplanar with the mean plane of the phenyl ring: C8—N7-phenyl: 0.128 (2)°.

Experimental

2,6-Dimethyl-4-(2-iodophenyl)quinoline (53.9 mg, 0.15 mmol) was dissolved in 1.5 ml of dichloromethane in a flame-dried Schlenk tube and at 273 K. 11.6 µL(17.1 mg, 0.15 mmol) of trifluoromethane sulfonic acid were added. While stirring and cooling, mCPBA (38.8 mg, 0.23 mmol) was added. After 10 min trifluoromethansulfonic acid (23.3 µL, 34.2 mg, 0.3 mmol) was added and stirring continued for 30 min. The solvent was removed in vacuo, diethyl ether (5 ml) was added. An oily layer separated which crystallized upon standing for 8 h. The crystalline solid was isolated by suction filtration and washed with cold ether. Yield: 27.8 mg of a mixture of two compounds (ca 1: 0.6). In a Schlenk tube, this product (380 mg) was suspended in toluene (10 ml) and benzyl amine (96.4 mg, 0.9 mmol), Pd₂(dba)₃ (27.6 mg, 0.03 mmol), Xanthphos (52.2 mg, 0.09 mmol) and Cs₂CO₃ (684.3 mg, 2.1 mmol) were added. The mixture was stirred over night at 373 K, cooled, filtered through celite and the filter cake was washed with ethyl acetate (50 ml). The pooled organic solutions were washed with water, brine, and dried over MgSO₄. After removal of the solvents in vacuo, the residue was purified by chromatography on Al₂O₃ with gradient elution starting with petroleum ether, followed by ethyl acetate and finally methanol. yield: 124.2 mg (0.35 mmol) of the title compound (R_f = 0.68 SiO₂, ethyl acetate/methanol = 1/1) as yellow crystals with m. p. = 497 - 499 K. 4-(2-(Benzylamino)phenyl-2,6-dimethylquinoline (60 mg, 0.18 mmol, colorless solid, m. p. = 448 - 450 K) was isolated as a first fraction (R_f = 0.56 (SiO₂, petroleum ether/ethyl acetate = 1/1)