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Synlett 2008(5): 655-658  
DOI: 10.1055/s-2008-1042800
LETTER
© Georg Thieme Verlag Stuttgart · New York

Indium(III) Trifluoromethanesulfonate: An Efficient Reusable Catalyst for the Alkynylation-Cyclization of 2-Aminoaryl Ketones and Synthesis of 2,4-Disubstituted Quinolines

Kushal C. Lekhok, Dipak Prajapati*, Ramesh C. Boruah
Department of Medicinal Chemistry, North East Institute of Science & Technology, Jorhat 785 006, Assam, India
Fax: +91(376)2370011; e-Mail: dr_dprajapati2003@yahoo.co.uk;
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Publication History

Received 3 October 2007
Publication Date:
26 February 2008 (online)

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Abstract

An environmentally friendly and highly efficient procedure for the preparation of 2,4-disubstituted quinoline derivatives has been developed by a simple alkynylation-cyclization reaction of 2-aminoaryl ketones with phenylacetylenes in the presence of indium(III) trifluoromethanesulfonate In(OTf)3 under microwave irradiation and solvent-free conditions. This catalyst can be recovered after the reaction and reused efficiently in subsequent runs.

Key words

2,4-disubstituted quinolines - solvent-free conditions - microwave irradiations - indium triflate

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General Procedure for the Synthesis of 2,4-Disubstituted Quinoline Derivatives under Microwave IrradiationsA mixture of 5-chloro-2-aminobenzophenone (1a, 1.65 g, 5 mmol), phenylacetylene (0.52 g, 5 mmol), and In(OTf)3 (0.03 g) was placed in a quartz reaction vessel of a Prolabo Synthwave Microwave Reactor 402 and allowed to react under microwave irradiation at 110 °C for 4.5 min. After completion (monitored by TLC), the reaction mixture was cooled to r.t. and cold MeOH (15 mL) added. The residue was filtered and the filtrate was evaporated to obtain the crude product which was then recrystallized from hot MeOH to afford quinoline 3a in 93% yield, mp 98 °C. The residue obtained after filtration contains In(OTf)3 which was used as such in another experiment and the corresponding 6-chloro-2,4-diphenylquinoline was isolated in 90% yield.6-Chloro-2,4-diphenylquinoline (3a): mp 98 °C. IR (KBr): 1610, 1375, 1270, 1160, 1125 cm-1. 1H NMR (CDCl3): δ = 7.10-7.23 (m, 8 H), 7.65 (m, 1 H), 7.95 (m, 1 H), 8.10-8.25 (m, 4 H). Anal. Calcd for C21H14ClN: C, 80.00; H, 4.44; N, 4.44. Found: C, 80.11; H, 4.52; N, 4.36. MS: m/z = 315 [M+].2,4-Diphenyl-quinoline (3b): mp 107 °C. IR (KBr): 1610, 1375, 1270, 1160, 1125 cm-1. 1H NMR (CDCl3): δ = 7.10-7.23 (m, 9 H), 7.65 (m, 1 H), 7.95 (m, 1 H), 8.10-8.25 (m, 4 H). Anal. Calcd for C21H15N: C, 89.69; H, 5.34; N, 4.98. Found: C, 89.75; H, 5.42; N, 4.88. MS: m/z = 281 [M+].2-Phenyl-4-(2′-chlorophenyl)-6-chloroquinoline (3c): mp 112 °C. IR (KBr): 1610, 1375, 1270, 1160, 1125 cm-1. 1H NMR (CDCl3): δ = 7.27 (s, 1 H), 7.39-7.84 (m, 7 H), 8.18 (s, 1 H), 8.19-8.21 (m, 4 H). Anal. Calcd for C21H13Cl2N: C, 72.21; H, 3.72, N, 4.01. Found: C, 72.13; H, 3.82; N, 4.12. MS: m/z = 349 [M+].2,4-Diphenyl-6-nitroquinoline (3d): mp 264 °C. IR (KBr): 1625, 1370, 1240, 1150, 1035 cm-1. 1H NMR (CDCl3): δ = 7.30-7.65 (m, 8 H), 7.80 (m, 1 H), 8.10-8.15 (m, 5 H). Anal. Calcd for C21H14N2O2: C, 77.30; H, 4.29; N, 8.59. Found: C, 77.39; H, 4.19; N, 8.66. MS: m/z = 326 [M+].2,4-Diphenyl-8-nitroquinoline (3e): mp 264 °C. IR (KBr): 1630, 1375, 1235, 1150, 1030 cm-1. 1H NMR (CDCl3): δ = 7.25-7.60 (m, 8 H), 7.75 (m, 1 H), 8.12-8.20 (m, 5 H). Anal. Calcd for C21H14N2O2: C, 77.30; H, 4.29; N, 8.59. Found: C, 77.42; H, 4.35; N, 8.48. MS: m/z = 326 [M+].2-Phenyl-4-(2′-fluorophenyl)-6-chloroquinoline (3f): mp 124 °C. IR (KBr): 1610, 1375, 1270, 1160, 1125 cm-1. 1H NMR (CDCl3): δ = 7.10-7.23 (m, 7 H), 7.65 (m, 1 H), 7.95 (m, 1 H), 8.10-8.25 (m, 4 H). Anal. Calcd for C21H13ClFN: C, 75.68; H, 3.90; N, 4.20. Found: C, 75.75; H, 3.98; N, 4.13. MS: m/z = 333 [M+].2-Phenyl-4-(2′-fluorophenyl)quinoline (3g): mp 90 °C. IR (KBr): 1610, 1375, 1270, 1160, 1125 cm-1. 1H NMR (CDCl3): δ = 7.10-7.23 (m, 7 H), 7.65 (m, 1 H), 7.95 (m, 1 H), 8.10-8.25 (m, 4 H). Anal. Calcd for C21H14FN: C, 84.28; H, 4.68; N, 4.68. Found: C, 84.36; H, 4.59; N, 4.78. MS: m/z = 299 [M+].