Synlett 2002(6): 0993-0995
DOI: 10.1055/s-2002-31902
LETTER
© Georg Thieme Verlag Stuttgart · New York

LPDE-Catalyzed Intramolecular Cyclization of Arylimines: A Facile Synthesis of Tetrahydrochromanoquinolines

J. S. Yadav*, B. V. Subba Reddy, C. Venkateswara Rao, R. Srinivas
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad-500 007, India
Fax: +91(40)7160512; e-Mail: yadav@iict.ap.nic.in;
Further Information

Publication History

Received 9 April 2001
Publication Date:
07 February 2007 (online)

Abstract

Lithium perchlorate in diethyl ether (LPDE) is found to catalyze an intrarmolecular cyclization of aldimines derived from aromatic amines and O-prenyl derivatives of salicylaldehydes to afford the corresponding tetrahydrochromano[4,3-b]quinoline derivatives in excellent yields with moderate diastereoselectivity.

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Experimental procedure: Method I: A mixture of prenyl derivative of salicylaldimine (5 mmol) and 5 M lithium perchlorate in diethyl ether (5 mL) was stirred at ambient temperature for an appropriate time (Table). After completion of the reaction, as indicated by TLC, the reaction mixture was quenched with water (15 mL) and extracted with diethyl ether (2 × 15 mL). The combined organic layers were dried over anhydrous Na2SO4, concentrated in vacuo and purified by column chromatography on silica gel (Merck, 100-200 mesh ethyl acetate-hexane, 0.5:9.5) to afford pure product.
Method II: A mixture of prenyl derivative of salicylaldimine (5 mmol) and Amberlyst 15 (1.5 g) in acetonitrile (10 mL) was stirred at ambient temperature for an appropriate time (Table). After completion of the reaction, as indicated by TLC, the reaction mixture was filtered and washed with ethyl acetate (2 × 10 mL) The combined organic layers were dried over anhydrous Na2SO4, concentrated in vacuo and purified by column chromatography on silica gel (Merck, 100-200 mesh ethyl acetate-hexane, 0.5:9.5) to afford pure product. The ion-exchange resin Amberlyst 15 was washed with methanol and reused in subsequent reaction without apparent loss of activity.
Spectral data for product 2b: Solid, mp146-147 °C; 1H NMR (CDCl3): δ 1.27 (s, 3 H), 1.50 (s, 3 H), 1.98 (dt, 1 H, J = 10.8, 3.5 Hz), 3.90 (brs, NH), 3.95 (t, 1 H, J = 10.8 Hz), 4.27 (dd, 1 H, J = 10.8, 3.5 Hz), 4.60 (d, 1 H, J = 3.5 Hz), 6.38 (d, 1 H, J = 8.0 Hz), 6.85-7.0 (m, 3 H), 7.05 (d, 1 H, J = 2.1 Hz), 7.10 (d, 2 H, J = 8.0 Hz); 13C NMR (CDCl3, proton decoupled): δ 25.4, 33.5, 40.1, 45.9, 63.3, 114.4, 116.8, 117.7, 120.4, 121.4, 122.5, 123.4, 124.5, 125.5, 127.1, 127.7, 128.2, 129.3, 129.4, 129.6, 138.9, 153.7; IR (KBr): 3381, 3087, 3030, 2960, 2933, 2891, 1697, 1574, 1499, 1478, 1329, 1245, 1059, 1030, 972 cm-1; EIMS : m/z 299 M+, 284, 254, 178, 168, 131, 117, 77. 3b: Oil, 1H NMR (CDCl3): δ 1.20 (s, 3 H), 1.45 (s, 3 H), 2.05 (dt, 1 H, J = 11.2, 3.3 Hz), 3.95 (t, 1 H, J = 11.2 Hz), 4.05 (brs, NH), 4.43 (d, 1 H, J = 11.2 Hz), 4.60 (dd, 1 H, J = 11.2, 3.3 Hz), 6.40 (d, 1 H, J = 8.0 Hz), 6.95-7.05 (m, 3 H), 7.10-7.25 (m, 3 H).
2e: Solid, mp130-131 °C; 1H NMR (CDCl3): δ 1.38 (s, 3 H), 1.45 (s, 3 H), 1.95 (dt, 1 H, J = 10.8, 3.5 Hz), 2.15 (s, 3 H), 3.60 (brs, NH), 3.80 (d, 1 H, J = 10.8 Hz), 4.20 (dd, 1 H, J = 10.8, 3.5 Hz), 4.60 (d, 1 H, J = 3.5 Hz), 6.55 (t, 1 H, J = 7.8 Hz), 6.80-6.98 (m, 3 H), 7.05 (d, 1 H, J = 8.0 Hz), 7.20 (m, 2 H); EIMS: m/z 281 M+, 265, 235, 149, 132, 116, 78; IR (KBr): 3392, 3225, 3028, 2988, 2831, 1651, 1568, 1488, 1274, 1181, 1048, 917 cm-1.
3e: Solid, mp122-123 °C; 1H NMR (CDCl3): δ 1.20 (s, 3 H), 1.40 (s, 3 H), 2.05 (dt, 1 H, J = 11.0, 3.0 Hz), 2.20 (s, 3 H), 3.95 (d, 1 H, J = 11.0 Hz), 4.05 (brs, NH), 4.40 (d, 1 H, J = 11.0 Hz), 4.50 (dd, 1 H, J = 11.0, 3.0 Hz), 6.70 (t, 1 H, J = 7.8 Hz), 6.85-7.05 (m, 3 H), 7.20 (m, 2 H), 7.40 (d, 1 H, J = 8.0 Hz).
2g: Solid, mp122-124 °C; 1H NMR (CDCl3): δ 1.30 (s, 3 H), 1.42 (s, 3 H), 1.90 (dt, 1 H, J = 11.0 and 3.3 Hz), 2.10 (s, 3 H), 3.60 (brs, NH), 3.70 (d, 1 H, J = 11.0 Hz), 4.18 (dd, 1 H, J = 11.0, 3.3 Hz), 4.50 (d, 1 H, J = 3.3 Hz), 5.0 (s, 2 H), 6.38 (d, 1 H, J = 8.0 Hz), 6.70-6.90 (m, 5 H), 7.25-7.35 (m, 5 H); 13C NMR (CDCl3): δ 20.6, 25.6, 33.2, 33.9, 40.9, 46.3, 63.6, 70.9, 113.5, 115.2, 116.5, 117.3, 124.4, 126.0, 126.8, 127.4, 127.8, 128.5, 137.2, 138.0, 148.0, 152.6; IR (KBr): 3395, 3168, 2855, 1655, 1598, 1460, 1275, 1182, 1048, 920 cm-1.