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Synlett 2008(8): 1185-1188  
DOI: 10.1055/s-2008-1072722
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Novel and Green Method for the Synthesis of Indeno[2,1-c]pyridine Derivatives in Ionic Liquid Catalyzed by Malononitrile

Xiang-Shan Wang*a,b, Jian-Rong Wua, Qing Lia, Chang-Sheng Yaoa, Shu-Jiang Tua,b
a School of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou, Jiangsu 221116, P. R. of China,
b The Key Laboratory of Biotechnology for Medical Plants, Xuzhou, Jiangsu 221116, P. R. of China
Fax: +86(516)83500065; e-Mail: xswang1974@yahoo.com; e-Mail: xswang@xznu.edu.cn;
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Publication History

Received 2 January 2008
Publication Date:
16 April 2008 (online)

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Abstract

1-Aryl-9H-indeno[2,1-c]pyridine-4-carbonitrile derivatives were unexpectedly obtained from the reaction of 2-(2,3-dihydroinden-3-ylidene) malononitrile, benzaldehyde and malononitrile in ionic liquid at 90 °C. Modification of the novel reaction protocol resulted in a two-component reaction between 2-(2,3-dihydroinden-3-ylidene) malononitrile, and benzaldehyde catalyzed by 10 mol% malononitrile. A 1,5-hydrogen transfer was proposed to occur in the formation of the product.

Key words

indeno[2,1-c]pyridine - ionic liquids - malononitrile - 1,5-hydrogen transfer - synthesis

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General Procedure for the Syntheses of 1-Aryl-9 H -indeno[2,1- c ]pyridine-4-carbonitrile Derivatives
A dry 50 mL flask was charged with benzaldehyde (2.0 mmol), malononitrile (0.2 mmol), 2-(2,3-dihydroinden-3-ylidene)malononitrile (2.0 mmol), and ionic liquid of [bmim+][BF4 -] (1 mL). The reaction mixture was stirred at 90 °C for 3-8 h. Then, H2O (5 mL) was added to the mixture, the solid was isolated by filtration. The water in the filtrate was removed by evaporation at reduced pressure, and the ionic liquid could be recovered easily 80 °C in vacuo for 4 h. The crude yellow products were washed with H2O and purified by recrystallization from DMF to give 4.
1-(4-Methylphenyl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (4a): mp 201-203 °C. 1H NMR (400 MHz, CDCl3): d = 2.43 (s, 3H, CH3), 4.02 (s, 2H, CH2), 7.29 (d, J = 8.0 Hz, 2H, ArH), 7.44-7.52 (m, 4H, ArH), 7.58-7.60 (m, 1H, ArH), 8.31 (s, 1H, ArH), 8.59 (d, J = 8.0 Hz, 1H, ArH) ppm. 13C NMR (100 MHz, CDCl3): δ = 167.2, 147.3, 141.1, 137.5, 136.6, 135.7, 134.3, 132.4, 130.9, 129.8, 128.2, 126.0, 125.3, 115.4, 115.1, 112.4, 37.4, 21.6 ppm. HRMS (EI): m/z calcd for C20H14N2 [M+]: 282.1157; found: 282.1151. IR (KBr): ν = 3052, 2215, 1619, 1603, 1523, 1414, 1331, 1314, 1218, 1188, 1164, 1122, 1105, 1019, 942, 896, 848, 806, 770, 720 cm-1.