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22
General Procedure for 2
H
-Chromenes 7-10: A mixture of the naphthoquinone (0.02 mol), allyltriphenylphosphonium salt (0.04 mol), CHCl3 (15 mL) and aq 50% NaOH (15 mL, 0.19 mol) was vigorously stirred for 48 h at r.t. The organic phase was collected, washed with H2O (3 × 10 mL), dried over MgSO4 and the solvent was evaporated. Purification of the crude product was achieved by flash column chromatography using hexane-CH2Cl2 as eluent.
6-Methoxy-3,3-dimethyl-3
H
-benzo[
f
]chromene (7a): IR (KBr): 2971, 2938, 1634, 1588, 1574, 1515, 1464, 1450, 1443, 1411, 1379, 1351, 1283, 1247, 1220, 1207, 1199, 1160, 1130, 1119, 1092, 996, 981, 885, 841, 755, 727, 694, 626 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.50 (s, 6 H, Me), 3.98 (s, 3 H, OMe), 5.58 (d, J = 9.8 Hz, 1 H, H-2), 6.48 (s, 1 H, H-5), 6.95 (d, J = 9.8 Hz, 1 H, H-1), 7.30 (ddd, J = 1.2, 6.8, 8.5 Hz, 1 H, H-8), 7.49 (ddd, J = 1.2, 6.8, 8.3 Hz, 1 H, H-9), 7.89 (ddd, J = 0.7, 1.2, 8.3 Hz, 1 H, H-7), 8.17 (ddd, J = 0.7, 1.2, 8.5 Hz, 1 H, H-10). 13C NMR (75.0 MHz, CDCl3): δ = 27.4 (Me), 27.4 (Me), 55.5 (OMe), 76.2 (C-3), 97.4 (C-5), 106.8 (C-10b), 118.1 (C-1), 120.9 (C-10), 121.3 (C-6a), 122.3 (C-7), 122.5 (C-8), 126.0 (C-2), 127.1 (C-9), 130.4 (C-10a), 151.6 (C-4a), 156.4 (C-6). EIMS: m/z (%) = 240 (22) [M+], 225 (100), 210 (15). HRMS: m/z calcd for C16H16O2: 240.1150; found: 240.1139.
2,2,6,6-Tetramethyl-3,4-dihydro-2
H
,6
H
-1,5-dioxatri-phenylene (8a): mp 89-90 °C. IR (KBr): 2975, 2934, 1637, 1578, 1510, 1465, 1453, 1428, 1418, 1396, 1383, 1369, 1360, 1325, 1289, 1253, 1237, 1220, 1195, 1159, 1137, 1119, 1003, 974, 881, 762, 732, 710, 691, 665, 646 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.41 (s, 6 H, Me), 1.47 (s, 6 H, Me), 1.86 (t, J = 6.8 Hz, 2 H, H-3), 2.77 (t, J = 6.8 Hz, 2 H, H-4), 5.54 (d, J = 10.0 Hz, 1 H, H-7), 6.95 (d, J = 10.0 Hz, 1 H, H-8), 7.27 (ddd, J = 1.2, 6.8, 8.3 Hz, 1 H, H-11), 7.41 (ddd, J = 1.2, 6.8, 8.3 Hz, 1 H, H-10), 7.85 (ddd, J = 0.5, 1.2, 8.3 Hz, 1 H, H-12), 8.14 (ddd, J = 0.5, 1.2, 8.3 Hz, 1 H, H-9). 13C NMR (75 MHz, CDCl3): δ = 19.9 (C-4), 29.3 (Me), 29.3 (Me), 78.6 (C-6), 34.7 (C-3), 77.1 (C-2), 78.6 (C-6), 106.6 (C-8a), 110.3 (C-4a), 121.2 (C-9), 123.3 (C-12), 123.6 (C-12a), 124.6 (C-11), 124.8 (C-8), 128.0 (C-7), 128.7 (C-10), 131.6 (C-8b), 152.5 (C-4b), 152.6 (C-13). EIMS: m/z (%) = 294 (44) [M+], 279 (77), 223 (100). HRMS: m/z calcd for C20H22O2: 294.1620; found: 294.1617.
5,6,7,8-Tetrachloro-2,2-dimethyl-2
H
-chromene (10): yellow solid; mp 83-84 °C. IR (KBr): 2924, 2870, 2854, 1681, 1600, 1455, 1428, 1392, 1379, 1327, 1308, 1237, 1225, 1205, 1151, 1051, 1018, 996, 970, 924, 900, 834, 791, 663 cm-1. 1H NMR (300 MHz, CDCl3): δ = 1.87 (d, J = 1.5 Hz, 3 H, Me), 1.88 (d, J = 1.5 Hz, 3 H, Me), 5.55 (dsept, J = 1.5, 8.3 Hz, 1 H, H-2), 6.92 (d, J = 8.3 Hz, 1 H, H-1). 13C NMR (75 MHz, CDCl3): δ = 19.0 (Me), 26.4 (Me), 30.0 (C-3), 111.0 (C-1), 112.9 (C-5), 118.3 (C-2), 125.1 (C-8a), 126.0 (C-7), 128.0 (C-6), 144.9 (C-8), 146.7 (C-4a).