Facile synthesis of 3-aryl-4-iodobenzo[b][1,6]naphthyridines

Full text of DOI:10.1007/s10593-009-0206-x

Chemistry of Heterocyclic Compounds, Vol. 44, No. 11, 2008
LETTERS TO THE EDITOR
FACILE SYNTHESIS OF 3-ARYL-
4-IODOBENZO[b][1,6]NAPHTHYRIDINES
S. Rudys and I. Cikotiene
Keywords: alkynes, benzo[b][1,6]naphthyridines, tert-butylimines, cyclization.
In continuing our research on intramolecular cyclizations of alkynes that possess a nucleophile in close
proximity to the carbon-carbon triple bond [1, 2] we have performed a facile synthesis of 3-aryl-4-iodobenzo-
[b][1,6]naphthyridines. The latter compounds attract our attention as starting materials for preparation of more
complex polyaromatic systems which could be of interest for practical applications, especially for OLED
(organic light-emitting diode). Thus, reaction of 2-arylethynylquinoline-3-carbaldehydes 1a,b with tert-butyl-
amine in sealed tubes at 100°C gave the corresponding tert-butylimines 2a,b. The latter two compounds
underwent smooth iodine-mediated ring closure reaction and the corresponding 3-aryl-4-iodobenzo-
[b][1,6]naphthyridines 3a,b were formed. In this reaction, the iodine attacks the triple bond of compounds 2a,b
first, therefore nucleophilic attack of the neighboring tert-butylimino group becomes more favorable [3].
ii
O
i
N
N
N
2a,b
1a,b
R
R
N
N
I
3a,b
R
1–3 a R = H; b R = Et
Reagents and conditions: i – t-BuNH2, sealed tube, 100°C, 24 h;
ii – I2, MeCO2Na, MeCN, r. t., 5 h
The IR spectra were obtained on a Spectrum BX II FT-IR spectrophotometer (Perkin–Elmer) in KBr
1
13
disks. The H and C NMR spectra were recorded on a Varian Unity Inova (300 and 75 MHz, respectively) in
CDCl3, internal standard TMS.
__________________________________________________________________________________________
Vilnius University, Faculty of Chemistry, Department of Organic chemistry, Vilnius LT-03225,
Lithuania; e-mail: inga.cikotiene@chf.vu.lt. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11,
pp. 1739-11740, October, 2008. Original article submitted August 29, 2008, 2008.
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0009-3122/08/4411-1416©2008 Springer Science+Business Media, Inc.

The starting 2-arylethynylquinoline-3-carbaldehydes 1a,b were synthesized according to the method of [4].
N-(tert-Butyl)-N-{(1E)-[2-(arylethynyl)quinolin-3-yl]methylene}amines (2a,b). mixture of the
A
corresponding 2-arylethynylquinoline-3-carbaldehyde 1a,b (0.2 mmol) and tert-butylamine (3 ml) in a tube was
flushed with argon and the tube was carefully sealed. The mixture was heated at 100°C for 24 h. The solvent
was evaporated under reduced pressure, and compounds 2a,b were recrystallized.
N-(tert-Butyl)-N-{(1E)-[2-(phenylethynyl)quinolin-3-yl]methylene}amine (2a). Yield 92%; mp
1
144-146°C (octane). IR spectrum, ν, сm–1: 2202 (C≡C). H NMR spectrum, δ, ppm (J, Hz): 1.44 (9H, s,
C(CH3)3); 7.43–7.46 (3H, m, ArH); 7.58 (1H, ddd, J = 7.5, J = 6.0, J = 0.9, CH); 7.69–7.72 (2H, m, ArH); 7.94
(1H, d, J = 7.5, CH); 8.16 (1H, d, J = 8.7, CH); 8.85 (1H, s, CH); 9.08 (1H, s, CH). 13С NMR spectrum, δ, ppm:
29.7, 58.3, 86.8, 94.3, 122.0, 127.3, 127.5, 128.6, 128.7, 129.1, 129.4, 130.7, 130.8, 132.1, 133.6, 143.4, 148.8,
152.8. Found, %: C 84.68; H 6.34; N 9.02. C22H20N2. Calculated, %: C 84.58; H 6.45; N 8.97.
N-(tert-Butyl)-N-{(1E)-[2-(4-ethylphenylethynyl)quinolin-3-yl]methylene}amine (2b). Yield 87%;
1
mp 122–124°C (octane). IR spectrum, ν, сm–1: 2204 (C≡C). H NMR spectrum, δ, ppm (J, Hz): 1.30 (3H, t,
J = 7.8, CH3); 1.44 (9H, s, C(CH3)3); 2.73 (2H, q, J = 7.8, CH2); 7.28 (2H, d, J = 8.1, ArH); 7.58 (1H, ddd,
J = 7.5, J = 6.0, J = 0.9, CH); 7.62 (2H, d, J = 8.1, ArH); 7.78 (1H, ddd, J = 7.2, J = 6.9, J = 1.5, CH); 7.93 (1H,
d, J = 8.4, CH); 8.15 (1H, d, J = 8.4, CH); 8.84 (1H, s, CH); 9.09 (1H, s, CH). 13С NMR spectrum, δ, ppm: 15.2,
28.9, 29.7, 58.3, 86.4, 94.8, 127.2, 127.3, 128.1, 128.6, 129.0, 130.7, 130.8, 132.1, 133.5, 143.6, 146.1, 148.8,
152.9. Found, %: C 84.55; H 7.04; N 8.09. C24H24N2. Calculated, %: C 84.67; H 7.11; N 8.23.
3-Aryl-4-iodobenzo[b][1,6]naphthyridines 3a,b. A mixture of the corresponding N-(tert-butyl)-
N-{(1E)-[2-(arylethynyl)quinolin-3-yl]methylene}amine 2a,b (1 mmol), iodine (1.54 g, 6 mmol), and sodium
acetate (0.25 g, 3 mmol) in acetonitrile (5 ml) was stirred at room temperature for 5 h. The reaction mixture was
diluted with ether (25 ml), washed with sat. Na2S2O3 (25 ml), dried over sodium sulfate and evaporated.
1
4-Iodo-3-phenylbenzo[b][1,6]naphthyridine (3a). Yield 90%; mp 108–110°C. H NMR spectrum, δ,
ppm (J, Hz): 7.51–7.59 (3H, m, ArH); 7.71 (1H, ddd, J = 7.3, J = 6.5, J = 1.1, CH); 7.80–7.82 (2H, m, ArH);
7.99 (1H, ddd, J = 7.3, J = 6.8, J = 1.2, CH); 8.17 (1H, d, J = 8.7, CH); 8.47 (1H, d, J = 9.0, CH); 8.99 (1H, s,
CH); 9.43 (1H, s, CH). 13С NMR spectrum, δ, ppm: 101.3, 120.9, 127.3, 127.6, 127.7, 128.7, 128.8, 130.3,
133.1, 138.1, 140.7, 145.1, 149.5, 152.6, 154.2, 159.7. Found, %: C 56.75; H 3.00; N 7.46. C18H11IN2.
Calculated, %: C 56.57; H 2.90; N 7.33.
3-(4-Ethylphenyl)-4-iodobenzo[b][1,6]naphthyridine (3b). Yield 80%; mp 94–96°C. 1H NMR
spectrum, δ, ppm (J, Hz): 1.43 (3H, t, J = 7.8, CH3); 2.80 (2H, q, J = 7.8, CH2); 7.39 (2H, d, J = 7.8, ArH); 7.67
(1H, ddd, J = 7.3, J = 6.5, J = 1.1, CH); 7.76 (2H, d, J = 7.8, ArH); 7.96 (1H, ddd, J = 7.4, J = 6.6, J = 1.2, CH);
8.12 (1H, d, J = 8.7, CH); 8.42 (1H, d, J = 9.0, CH); 8.92 (1H, s, CH); 9.38 (1H, s, CH). 13С NMR spectrum, δ,
ppm: 15.4, 28.7, 100.9, 120.7, 127.0, 127.3, 127.4, 128.4, 128.5, 129.9, 132.8, 137.6, 140.3, 144.8, 149.2, 152.3,
153.9, 159.4. Found, %: C 58.77; H 3.58; N 7.00. C20H15IN2. Calculated, %: C 58.55; H 3.69; N 6.83.
The work was supported by the Lithuanian Science and Study Foundation, Reg. No. T-08032, Grant
No. T-18/08.
REFERENCES
1.
2.
I. Cikotiene, M. Morkunas, D. Motiejaitis, and S. Rudys, A. Brukstus, Synlett, 1693 (2008).
I. Cikotiene, R. Buksnaitiene, and A. Brukstus, Khim. Geterotsikl. Soed., 619 (2007). [Chem. Heterocycl.
Comp., 43, 515 3. (2007)].
3.
4.
Q. Huang, J. A. Hunter, and R. C. Larock, Org. Lett., 2973 (2001).
P. Amaury and P. Belmont, Synthesis, 2400 (2005).
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