Synlett 2003(2): 0250-0252
DOI: 10.1055/s-2003-36796
LETTER
© Georg Thieme Verlag Stuttgart · New York

Novel Microwave-assisted [3+3] Cyclocondensations with 1-Cyanomethylene Tetrahydroisoquinoline

Péter Nemes*a, Zoltán Vinczea, Barbara Balázsb, Gábor Tóthb, Pál Scheibera
a Department of Chemistry, Faculty of Veterinary Science, Szent István University, H-1400 Budapest, P.O.Box 2, Hungary
Fax: 36(1)478 4268; e-Mail: pnemes@univet.hu;
b Technical Analytical Research Group, Institute for General and Analytical Chemistry, Technical University, H-1111 Budapest, Szent Gellért tér 4, Hungary
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Publikationsverlauf

Received 31 October 2002
Publikationsdatum:
22. Januar 2003 (online)

Abstract

α,β-Unsaturated aldehydes and ketones react with 1-cyanomethylene-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline in microwave-enhanced reactions affording regioselectively 6,7-dihydro-4H-benzo[a]quinolizines and 6,7-dihydro-2H-benzo[a]quinolizines, respectively.

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Experimental procedure: 2.4 mmol (520 mg) of 1 was mixed with 3.2 mmol of the carbonyl compound, and the reaction mixture was irradiated in an open vessel for 4 minutes in a Synthewave S402 (Prolabo) monomode, focused MW (2,45 GHz) reactor with continuous rotation. During the irradiation, the temperature of the reaction mixture (measured by infrared thermometry) raised linearly and reached its maximum between 140-170 °C depending on the enone after ca. 180 seconds. The oily mixture was then cooled and the product was either crystallised from an appropriate solvent (EtOH) or purified by flash chromatography. Yield: 72-85%.

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All isolated compounds were fully characterised by 1H and 13C NMR analysis. Representative data are given as follows: 4b: 1H NMR δ = 7.88 (s, 1 H, H-11), 7.37 (d, 1 H, J = 1.8 Hz, 4-furanyl), 6.64 (s, 1 H, H-8), 6.32 (dd, 1 H, 4-furanyl), 6.30 (d, 1 H, 4-furanyl), 6.28 (d, 1 H, H-2), 5.28 (dd, 1 H, H-3), 5.20 (d, 1 H, H-4), 3.94 (s, 3 H, 9-MeO), 3.90 (s, 3 H, 10-MeO), 3.41 (m, 1 H, H-6), 3.40 (m, 1 H, H-6), 2.89 (dd, 1 H, H-7), 2.74 (dt, 1 H, H-7); 13C NMR δ = 153.7 (4-furanyl), 150.6 (C-9), 150.2 (C-11b), 147.3 (C-10), 142.6 (4-furanyl), 129.5 (C-7a), 125.5 (C-2), 123.6 (1-CN), 121.0 (C-11a), 111.0 (C-11), 110.5 (4-furanyl), 110.1 (C-3), 110.0 (C-8), 108.5 (4-furanyl), 74.9 (C-1), 57.6 (C-4), 56.2 (9-MeO), 56.0 (10-MeO), 48.0 (C-6), 29.4 (C-7). 3 (R4 = 2-furanyl, R1, R2, R3 = H): 1H NMR δ = 7.87 (s, 1 H, H-11), 7.39 (d, 1 H, J = 2.0 Hz, 2-furanyl), 6.65 (s, 1 H, H-8), 6.34 (dd, 1 H, 2-furanyl), 6.18 (d, 1 H, 2-furanyl), 6.09 (d, 1 H, H-4), 4.87 (dd, 1 H, H-3), 4.53 (d, 1 H, H-2), 3.93 (s, 3 H, 9-MeO), 3.90 (s, 3 H, 10-MeO), 3.52 (m, 1 H, H-6), 3.42 (m, 1 H, H-6), 2.90 (m, 1 H, H-7), 2.76 (m, 1 H, H-7); 13C NMR δ = 157.6 (2-furanyl), 150.5 (C-9), 147.4 (C-10), 146.3 (C-11b), 142.1 (2-furanyl), 130.7 (C-4), 130.0 (C-7a), 123.3 (1-CN), 120.1 (C-11a), 111.3 (C-11), 110.3 (C-8), 110.4 (2-furanyl), 105.5 (2-furanyl), 100.4 (C-3), 73.6 (C-1), 56.3 (9-MeO), 56.0 (10-MeO), 48.8 (C-6), 36.2 (C-2), 29.4 (C-7). 5a: 1H NMR δ = 8.11 (d, 2 H, H-2′′), 8.09 (d, 1 H, J = 8.4 Hz, H-4), 7.82 (d, 1 H, J = 8.4 Hz, H-5), 7.51 (t, 1 H, H-4′′), 7.50 (t, 2 H, H-3′′), 7.22 (s, 1 H, H-5′), 7.02 (s, 1 H, H-2′), 6.68 (dd, 1 H, J = 11.0; 17.4 Hz, CH=), 5.64 (d, 1 H, J = 17.4 Hz, CH 2=), 5.20 (d, 1 H, J = 11.0 Hz, CH 2=), 4.00 (s, 3 H, 4′-MeO), 3.95 (s, 3 H, 3′-MeO); 13C NMR δ = 161.9 (C-2), 159.6 (C-6), 150.4 (C-4′), 148.8 (C-3′), 141.7 (C-4), 137.6 (C-1′′), 134.3 (CH=), 130.8 (C-3′′), 130.1 (C-6′), 129.3 (C-1′), 129.2 (C-4′′), 127.7 (C-2′′), 118.0 (C-5), 117.6 (3-CN), 114.7 (CH2=), 112.9 (C-2′), 108.8 (C-5′), 108.3 (C-3), 56.3 (3′-MeO), 56.2 (4′-MeO). 6 E: 1H NMR δ = 7.94 (s, 1 H, H-8), 7.43 (d, 2 H, Ph), 7.31 (t, 2 H, Ph), 7.20 (t, 1 H, Ph), 6.86 (d, 1 H, H-3′), 6.81 (d, 1 H, H-2′), 6.70 (s, 1 H, H-5), 5.41 (s, 1 H, H-2), 3.98 (s, 3 H, 7-MeO), 3.93 (s, 3 H, 6-MeO), 3.41 (t, 2 H, H-3), 2.83 (dd, 2 H, H-4); 13C NMR δ = 151.6 (C-1), 151.0 (C-6), 147.4 (C-7), 137.7 (Ph), 131.2 (C-4a), 128.6 (Ph), 127.0 (C-3′), 126.9 (Ph), 126.0 (Ph), 122.0 (1′-CN), 120.5 (C-8a), 120.3 (C-2′), 111.9 (C-8), 110.6 (C-5), 76.9 (C-1′), 56.3
(7-MeO), 56.0 (6-MeO), 39.6 (C-3), 29.9 (C-4). 6 Z: 1H NMR δ = 7.30 (d, 2 H, Ph), 7.27 (t, 2 H, Ph), 7.18 (s, 1 H, H-8), 7.13 (t, 1 H, Ph), 7.11 (d, 1 H, H-2′), 6.78 (s, 1 H, H-5), 6.61 (d, 1 H, H-3′), 5.80 (s, 1 H, H-2), 3.96 (s, 3 H, 7-MeO), 3.83 (s, 3 H, 6-MeO), 3.40 (t, 2 H, H-3), 2.83 (dd, 2 H, H-4); 13C NMR δ = 151.6 (C-1), 151.0 (C-6), 147.2 (C-7), 138.1 (Ph), 131.8 (C-4a), 128.6 (Ph), 123.4 (C-2′), 126.2 (Ph), 125.3 (Ph), 122.0 (1′-CN), 120.6 (C-8a), 123.7 (C-3′), 113.2 (C-8), 110.8 (C-5), 77.2 (C-1′), 56.3 (7-MeO), 56.0 (6-MeO), 39.6 (C-3), 30.1 (C-4).