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DOI: 10.1055/s-2003-40826
First Diels-Alder Reactions of 3-Styrylchromones under Microwave Irradiation
Publication History
Publication Date:
24 July 2003 (online)
Abstract
Microwave irradiation in solvent-free conditions induces Diels-Alder cycloaddition reactions of 3-styrylchromones with N-methyl and N-phenylmaleimide giving 4-aryl-1,3-dioxopyrrolo[3,4-c]-3a,4,11a,11b-tetrahydroxanthones in good yields. This is the first example of [4+2] cycloaddition reactions of 3-styrylchromones.
Key words
Diels-Alder reactions - microwave irradiation - 3-styrylchromones - N-methyl - N-phenylmaleimide
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References
Sandulache, A.; Silva, A. M. S.; Pinto, D. C. G. A.; Cavaleiro, J. A. S. unpublished results.
13Typical Experimental Procedure: A mixture of N-methyl-maleimide and the appropriate 3-styrylchromone (1 or 5) (4:1 mole ratio) was irradiated at atmospheric pressure in a focused microwave reactor (Prolabo MX350) at 270 W for 30 min (final temperature 160 °C). The crude products were purified by flash chromatography on silica gel (Merck type 60, 230-400 mesh), using a 2:1 mixture of hexane:ethyl acetate.
14Typical Experimental Procedure: A mixture of the appropriate 3-styrylchromone (1 or 5) and N-phenylmaleimide (1:3 mole ratio) was irradiated at atmospheric pressure in a focused microwave reactor (Prolabo MX350) at 270 W for 30 min (final temperature 200 °C, except for 4′-ethoxy-2-styrylchromones 1c or 5c which was 160 °C). The crude products were purified by flash chromatography on silica gel (Merck type 60, 230-400 mesh); using a 4:1 mixture of hexane:EtOAc the endo cycloadducts were collected while the exo cycloadducts were eluted with a 2:1 mixture of hexane:EtOAc.
15Selected Physical Data: 4-(4-chlorophenyl)-2-methyl-1,3-dioxopyrrolo[3,4-c]-3a,4,11a,11b-tetrahydroxanthone 2b: 1H NMR (300.13 MHz, CDCl3): δ = 2.98 (s, 3 H, 2-CH 3), 3.43 (d broad, 1 H, J = 8.6 Hz, H-3a), 3.81 (t, 1 H, J = 8.6 Hz, H-11b), 4.60 (d broad, 1 H, J = 7.0 Hz, H-4), 5.33 (ddd, 1 H, J = 8.6, 3.0 and 0.9 Hz, H-11a), 7.02 (dd, 1 H, J = 8.0 and 0.8 Hz, H-10), 7.06 (ddd, 1 H, J = 7.9, 7.3 and 0.8 Hz, H-8), 7.14 (d, 2 H, J = 8.4 Hz, H-3′,5′), 7.31 (d, 2 H, J = 8.4 Hz, H-2′,6′), 7.34 (ddd, 1 H, J = 7.0, 3.0 and 0.6 Hz, H-5), 7.51 (ddd, 1 H, J = 8.0, 7.3 and 1.7 Hz, H-9), 7.91 (dd, 1 H, J = 7.9 and 1.7 Hz, H-7). 13C NMR (75.47 MHz, CDCl3): δ = 25.3 (2-CH3), 38.5 (C-4), 43.3 (C-11b), 44.7 (C-3a), 70.9 (C-11a), 118.1 (C-10), 120.3 (C-6a), 122.3 (C-8), 127.5 (C-7), 128.3 (C-2′,6′), 129.3 (C-3′,5′), 133.1 (C-5a), 133.5 (C-4′), 136.1 (C-5), 136.4 (C-1′), 136.5 (C-9), 160.1 (C-10a), 173.5 (C-1), 176.8 (C-3), 178.8 (C-6). EI-MS: m/z (rel. int.) = 393 (100) [M+ ], 307 (50), 281 (60), 268 (43), 247 (7), 215 (14), 197 (27), 188 (25), 152 (45), 136 (11), 121 (64), 92 (20), 77 (11), 63 (14).
16Selected Physical Data: 2,4-diphenyl-1,3-dioxo-pyrrolo[3,4-c]-3a,4,11a,11b-tetrahydroxanthone 3a: 1H NMR (300.13 MHz, CDCl3): δ = 3.61 (ddd, 1 H, J = 8.5, 1.2 and 0.8 Hz, H-3a), 3.93 (t, 1 H, J = 8.5 Hz, H-11b), 4.73 (d broad, 1 H, J = 6.7 Hz, H-4), 5.43 (ddd, 1 H, J = 8.5, 2.5 and 1.2 Hz, H-11a), 7.04 (dd, 1 H, J = 7.8 and 1.0 Hz, H-10), 7.10 (ddd, 1 H, J = 7.7, 7.5 and 1.0 Hz, H-8), 7.20-7.29 (m, 4 H, H-2′,6′,2′′,6′′), 7.31-7.48 (m, 7 H, H-5,3′,4′,5′,3′′,4′′,5′′), 7.52 (ddd, 1 H, J = 7.8, 7.5 and 1.8 Hz, H-9), 7.99 (dd, 1 H, J = 7.7 and 1.8 Hz, H-7). 13C NMR (75.47 MHz, CDCl3): δ = 38.5 (C-4), 43.2 (C-11b), 45.5 (C-3a), 70.7 (C-11a), 118.2 (C-10), 121.1 (C-6a), 122.6 (C-8), 126.3 (C-2′′,6′′), 127.3 (C-2′,6′), 127.8 e/ou 127.9 (C-7,4′), 128.8 (C-4′′), 129.3 (C-3′,5′), 129.4 (C-3′′,5′′), 131.7 (C-1′′), 132.7 (C-5a), 136.5 (C-9), 137.1 (C-5), 138.5 (C-1′), 160.3 (C-10a), 172.8 (C-1), 175.7 (C-3), 180.1 (C-6). EI-MS: m/z (rel. int.) = 421 (68) [M+ ], 330 (14), 301 (9), 273 (100), 247 (36), 215 (13), 197 (55), 183 (22), 171 (25), 152 (75), 139 (16), 131 (32), 121 (77), 110 (32), 103 (21), 91 (65), 77 (72), 64 (43).
17Selected Physical Data: 2,4-diphenyl-1,3-dioxo-pyrrolo[3,4-c]-3a,4,11a,11b-tetrahydroxanthone 4a: 1H NMR (300.13 MHz, CDCl3): δ = 3.53 (dt, 1 H, J = 3.1 and 2.3 Hz, H-4), 3.58 (dd, 1 H, J = 8.5 and 3.1 Hz, H-11b), 4.42 (ddd, 1 H, J = 8.5, 3.1 and 2.3 Hz, H-3a), 5.28 (dt, 1 H, J = 3.1 and 1.3 Hz, H-11a), 5.81 (dt, 1 H, J = 2.3 and 1.3 Hz, H-5), 6.87 (dd, 1 H, J = 8.4 and 0.9 Hz, H-10), 7.10 (ddd, 1 H, J = 7.7, 7.5 and 0.9 Hz, H-8), 7.31-7.43 (m, 8 H, H-2′,3′,4′,5′,6′,2′′,4′′,6′′), 7.47-7.54 (m, 3 H, H-9,3′′,5′′), 7.96 (dd, 1 H, J = 7.7 and 1.7 Hz, H-7). 13C NMR (75.47 MHz, CDCl3): δ = 40.1 (C-3a), 44.3 (C-11b), 47.9 (C-4), 73.0 (C-11a), 118.1 (C-10), 119.5 (C-5), 119.9 (C-6a), 122.6 (C-8), 126.4 (C-2′,4′,6′), 127.6 (C-7), 128.4 (C-2′′,6′′), 128.3 (C-3′,5′), 128.7 (C-4′′), 129.2 (C-3′′,5′′), 131.8 (C-1′′), 135.5 (C-5a), 136.8 (C-9), 138.8 (C-1′), 159.5 (C-10a), 173.2 (C-1), 174.3 (C-3), 190.7 (C-6). EI-MS: m/z (rel. int.) = 421 (6) [M+ ], 301 (17), 273 (4), 154 (100), 120 (20), 92 (23), 77 (6), 64 (6).