Synlett 2011(15): 2187-2190  
DOI: 10.1055/s-0030-1261198
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

One-Pot Synthesis of Pyrano[2,3-b]quinolines from Enaminones under Solvent-Free Conditions

Dexuan Xiang, Xiaoqing Xin, Xu Liu, Santosh Kumar, Dewen Dong*
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. of China
e-Mail: dwdong@ciac.jl.cn;
Further Information

Publication History

Received 15 May 2011
Publication Date:
30 August 2011 (online)

Abstract

A facile and efficient one-pot synthesis of pyrano[2,3-b]quinolines has been developed via the Combes-type reaction of readily available enaminones, 2-arylamino-3-acetyl-5,6-dihydro-4H-pyrans, mediated by trifluoromethanesulfonic acid under solvent-free conditions.

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Typical Procedure for the Synthesis of Pyrano[2,3- b ]quinolines (2a as an example)
The substrate 1a (217 mg, 1.0 mmol) and CF3SO3H (0.35 mL, 4.0 mmol) was well stirred at 80 ˚C for 6.0 h. When the substrate 1a had been consumed (monitored by TLC), the mixture was poured into sat. aq NaCl (50 mL), neutralized with sat. aq NaHCO3, and extracted with CH2Cl2 (3 × 20 mL). The combined organic phase was washed with H2O (3 × 20 mL), dried over MgSO4, filtered, and concentrated in vacuo. The crude product was purified by flash chroma-tography (silica gel, PE-Et2O = 2:1) to give 2a as a white solid (173 mg, 87%). Selected Data for Compound 2a
White solid; mp 158-161 ˚C. ¹H NMR (400 MHz, CDCl3): δ = 2.09-2.15 (m, 2 H), 2.55 (s, 3 H), 2.93 (t, J = 6.8 Hz, 2 H), 4.40 (t, J = 5.2 Hz, 2 H), 7.37 (t, J = 8.0 Hz, 1 H), 7.57 (t, J = 8.0 Hz, 1 H), 7.81 (d, J = 8.4 Hz 1 H), 7.87 (d, J = 8.4 Hz, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 13.3, 21.8, 23.4, 66.5, 116.4, 123.5, 125.0, 127.6, 128.5, 144.0, 145.3, 159.4. IR (KBr): 2945, 1591, 1502, 1408, 1317, 1246, 1178, 1124, 980, 756 cm. Anal. Calcd for C13H13NO: C, 78.36; H, 6.58; N, 7.03. Found: C, 78.12; H, 6.33; N, 7.31.

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For the analytical data of 2, see Supporting Information.