3.3. General Procedure for the Synthesis of Adducts 13a–d/14a–d and 15a–d/16a–d via a One-Step Reaction. Method B
A mixture of active methylene compounds
20a–
c (1 mol-equiv.), benzaldehydes
21a–
d (mol-equiv.) and the corresponding diene
2 (1 mol-equiv.), was placed in a 25 mL two-necked, round-bottomed flask (equipped with a reflux condenser, a rubber septum and under nitrogen atmosphere), and the mixture was stirred and was irradiated with an infrared lamp [
33] at 50 °C for ~30 min–6 h, under solvent-free conditions, until the consumption of the diene (
tlc). The reaction mixture was allowed to cool to room temperature, and then was purified by column chromatography on silica gel (230–400 mesh) using
n-hexane/EtOAc (98:2) as eluent, to afford the corresponding cycloadducts
13a–
d/
14a–
d and
15a–
d/16a–
d.
(5S*,6R*)-6-Ethoxycarbonyl-6-cyano-3,5-diphenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (7a). According to Method A, the reaction between 4a (0.330 g, 0.0016 mol) and diene 1 (0.250 g, 0.0013 mol), followed by flash column chromatography, afforded 7a (0.380 g, 73%) as a white solid: mp 145–146 °C; FT-IR (KBr) νmax 2928, 2362, 1757, 1713, 1598 cm−1; 1H NMR (500 MHz, CDCl3) δ 0.87 (t, J = 6.9 Hz, 3H, OCH2CH3), 2.65 (ddd, J = 17.1, 4.8, 1.5 Hz, 1H, H-4β), 3.13 (dddd, J = 17.1, 11.4, 4.2, 2.1 Hz, 1H, H-4α), 3.16 (dd, J = 16.8, 1.5 Hz, 1H, H-7α), 3.43–3.48 (m, 2H, H-5, H-7β), 3.92 (q, J = 6.9, 2H, OCH2CH3), 7.32–7.46 (m, 10H, H-Ar); 13C NMR (125 MHz, CDCl3) δ 13.3 (OCH2CH3), 25.6 (C-4), 31.4 (C-7), 46.5 (C-5), 49.6 (C-6), 63.2 (OCH2CH3), 117.2 (CN), 120.4 (C-3a), 125.0 (C-9), 125.1 (C-10), 128.0 (C-13), 128.1 (C-11), 128.8 (C-14), 129.5 (15), 130.1 (C-7a), 133.3 (C-8), 136.4 (C-12), 154.0 (C-2), 166.5 (CO2CH2CH3); HRMS (EI+) calcd for C22H16N4O4 388.1423, found (M+) 388.1436.
(5S*,6R*)-6-Ethoxycarbonyl-6-cyano-5-(4-methoxyphenyl)-3-(phenyl)-4,5,6,7-tetrahydrobenzo[d] oxazol-2-one (7b). According to Method A, the reaction between 4b (0.44 g, 0.0019 mol) and diene 1 (0.300 g, 0.0016 mol), followed by flash column chromatography, afforded 7b (0.330 g, 50%) as a pale yellow solid: mp 168–169 °C; FT-IR (KBr) νmax 2934, 2244, 1769, 1716, 1598 cm−1; 1H NMR (500 MHz, CDCl3) δ 0.94 (t, J = 7.2 Hz, 3H, OCH2CH3), 2.61 (ddd, J = 16.2, 4.8, 1.2 Hz, 1H, H-4β), 3.06 (dddd, J = 16.2, 11.4, 4.2, 1.2 Hz, 1H, H-4α), 3.14 (dd, J = 16.2, 2.1 Hz, 1H, 7α), 3.39–3.46 (m, 2H, H-5, H-7β), 3.78 (s, 3H, OCH3), 3.96 (q, J = 7.2 Hz, 2H, OCH2CH3), 6.85 (d, J = 8.7 Hz, 2H, H-14), 7.30 (d, J = 8.7 Hz, 2H, H-13), 7.36–7.48 (m, 5H, H-Ar); 13C NMR (125 MHz, CDCl3) δ 13.4 (OCH2CH3), 25.6 (C-4), 30.1 (C-7), 45.6 (C-5), 49.8 (C-6), 55.2 (OCH3), 63.1 (OCH2CH3), 114.3 (C-14), 117.5 (CN), 120.8 (C-3a), 125.4 (C-9), 128.3 (C-11), 128.6 (C-12), 129.6 (C-13), 129.9 (C-10), 130.4 (C-7a), 133.5 (C-8), 154.0 (C-2), 159.7 (C-15), 166.5 (CO2CH2CH3); HRMS (EI+) calcd for C16H16N2O3 418.1529, found (M+) 418.1526.
(5S*,6R*)-6-Ethoxycarbonyl-5-(4-chlorophenyl)-6-cyano-3-(phenyl)-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (7c). According to Method A, the reaction between 4c (0.452 g, 0.0019 mol) and diene 1 (0.300 g, 0.0016 mol), followed by flash column chromatography, afforded 7c (0.400 g, 60%) as a pale yellow solid: mp 175–177 °C; FT-IR (KBr) νmax 2910, 2256, 1762, 1710, 1566 cm−1; 1H NMR (300 MHz, CDCl3) δ 0.96 (t, J = 7.0 Hz, 3H, OCH2CH3), 2.63 (ddd, J = 16.8, 4.8, 1.8 Hz, 1H, H-4β), 3.05 (dddd, J = 16.8, 11.4, 4.8, 2.1 Hz, 1H, H-4α), 3.16 (dd, J = 16.5, 1.8 Hz, 1H, H-7α), 3.41 (ddd, J = 16.5, 4.2, 1.8 Hz, 1H, H-7β), 3.45 (dd, J = 11.4, 4.8 Hz, 1H, H-5), 3.98 (qd, J = 7.2, 2.0 Hz, 2H, OCH2CH3), 7.30–7.47 (m, 9H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.5 (OCH2CH3), 25.5 (C-4), 31.3 (C-7), 45.7 (C-5), 49.4 (C-6), 63.3 (OCH2CH3), 116.9 (CN), 120.2 (C-3a), 125.1 (C-9), 128.2 (C-11), 129.0 (C-10), 129.6 (C-13), 129.7 (C-14), 130.0 (C-7a), 133.2 (C-8), 134.8 (C-15), 134.9 (C-12), 154.0 (C-2), 166.4 (CO2CH2CH3); HRMS (EI+) calcd for C23H19N2O4Cl 422.1033, found (M+) 422.1032.
(5S*,6R*)-6-Ethoxycarbonyl-6-cyano-5-(4-nitrophenyl)-3-(phenyl)-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (7d). According to Method A, the reaction between 4d (0.47 g, 0.0019 mol) and diene 1 (0.300 g, 0.0016 mol), followed by flash column chromatography, afforded 7d (0.550 g, 80%) as a pale yellow solid: mp 161–163 °C; FT-IR (KBr) νmax 2982, 2246, 1770, 1743, 1600 cm−1; 1H NMR (300 MHz, CDCl3) δ 0.97 (t, J = 6.5 Hz, 3H, OCH2CH3), 2.68 (ddd, J = 18.5, 4.5, 1.5 Hz, 1H, H-4β), 3.09 (dddd, J = 18.5, 11.5, 4.5, 2.0 Hz, 1H, H-4α), 3.22 (dd, J = 16.5 Hz, 0.5, 1H, H-7α), 3.43 (ddd, J = 16.5, 4.5, 2.0 Hz, 1H, H-7β), 3.61 (dd, J = 12.0, 4.5 Hz, 1H, H-5), 4.01 (qd, J = 6.5, 1.6 Hz, 2H, OCH2CH3), 7.36–7.48 (m, 5H, H-Ar), 7.27 (d, J = 9.0 Hz, 2H, H-13), 8.21 (d, J = 9.0 Hz, 2H, H-14); 13C NMR (75.4 MHz, CDCl3) δ 13.5 (OCH2CH3), 25.4 (C-4), 30.5 (C-7), 45.7 (C-5), 49.0 (C-6), 63.6 (OCH2CH3), 116.5 (CN), 119.9 (C-3a), 123.9 (C-9), 125.0 (C-10), 128.3 (C-11), 129.4 (C-13), 129.7 (C-14), 129.7 (C-8), 133.0 (C-7a), 143.6 (C-12), 148.0 (C-15), 153.8 (C-2), 166.0 (CO2CH2CH3); HRMS (EI+) calcd for C23H19N3O6 433.1274, found (M+) 433.1272.
(5S*,6R*)-6-Ethoxycarbonyl-6-cyano-5-(3-nitrophenyl)-3-(phenyl)-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (7e). According to Method A, the reaction between 4e (0.413 g, 0.0019 mol) and diene 1 (0.300 g, 0.0016 mol), followed by flash column chromatography, afforded 7e (0.380 g, 55%) as a pale yellow solid: mp 180–181 °C; FT-IR (KBr) νmax 2925, 2244, 1771, 1741, 1531 cm−1; 1H NMR (500 MHz, CDCl3) δ 0.96 (t, J = 7.2 Hz, 3H, OCH2CH3), 2.69 (ddd, J = 16.8, 4.8, 1.5 Hz, 1H, H-4β), 3.12 (dddd, J = 16.8, 11.4, 5.7, 2.1 Hz, 1H, H-4α), 3.22 (dd, J = 16.8, 1.5 Hz, 1H, H-7α), 3.45 (ddd, J = 16.8, 3.9, 2.1 Hz, 1H, H-7β), 3.65 (dd, J = 11.4, 4.8 Hz, 1H, H-5), 4.01 (qd, J = 7.2, 1.8 Hz, 2H, OCH2CH3), 7.35–7.50 (m, 5H, H-Ar), 7.57 (t, J = 7.5 Hz, 1H, H-16), 7.83 (d, J = 7.5 Hz, 1H, H-17), 8.21 (dd, J = 7.5, 1.8 Hz, 1H, H-15), 8.26 (dd, J = 7.5, 1.8 Hz, 1H, H-13); 13C NMR (125 MHz, CDCl3) δ 13.9 (OCH2CH3), 24.7 (C-4), 31.9 (C-7), 45.8 (C-5), 49.5 (C-6), 64.0 (OCH2CH3), 116.3 (CN), 120.0 (C-3a), 123.7(C-13), 123.8 (C-15), 125.0 (C-9), 128.2 (C-11), 129.4 (C-10), 130.2 (C-7a), 130.3 (C-17), 133.3 (C-8), 134.2 (C-16), 139.0 (C-12), 148.2 (C-14), 153.8 (C-2), 166.2 (CO2CH2CH3). HRMS (EI+) calcd for C23H19N3O6 433.1273, found (M+) 433.1273.
6,6-Dicyano-3,5-diphenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (9a). According to Method A, the reaction between 5a (0.345 g, 0.0022 mol) and diene 1 (0.350 g, 0.0018 mol), followed by flash column chromatography, afforded 9a (0.510 g, 80%) as a pale yellow solid: mp 150–151 °C; FT-IR (KBr) νmax 2933, 2251, 1769, 1720, 1501 cm−1; 1H NMR (300 MHz, CDCl3) δ 2.76 (dd, J = 17.1, 5.4 Hz, 1H, H-4β), 3.02–3.13 (m, 2H, H-4α, H-7α), 3.41–3.49 (m, 1H, H-7β), 3.46 (dd, J = 10.8, 5.4 Hz, 1H, H-5), 7.35–7.50 (m, 10H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 24.5 (C-4), 32.5 (C-6), 37.3 (C-7), 46.6 (C-5), 113.3 (CN), 113.6 (CN), 121.1 (C-3a), 125.3 (C-9), 127.9 (C-15), 128.0 (C-14), 128.5 (C-11), 129.7 (C-13), 129.8 (C-10), 129.8 (C-7a), 132.8 (C-8), 134.9 (C-12), 153.6 (C-2); HRMS (EI+) calcd for C21H15N3O2 341.1164, found (M+) 341.1165.
6,6-Dicyano-5-(4-methoxyphenyl)-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (9b). According to Method A, the reaction between 5b (0.436 g, 0.0023 mol), and diene 1 (0.370 g, 0.0019 mol) followed by flash column chromatography, afforded 9b (0.400 g, 55%) as a pale yellow solid: mp 157–159 °C; FT-IR (KBr) νmax 2935, 2252, 2217, 1768, 1598 cm−1; 1H NMR (300 MHz, CDCl3) δ 2.73 (dd, J = 16.8, 4.8 Hz, 1H, H-4β), 2.97–3.03 (m, 1H, H-4α), 3.39–4.01 (m, 2H, H-7α, H-7β), 3.44 (dd, J = 10.5, 5.1 Hz, 1H, H-5), 3.78 (OCH3), 6.92 (d, J = 8.7 Hz, 2H, H-14), 7.33–7.39 (m, 5H, H-Ar), 7.45 (d, J = 8.5 Hz, 2H, H-13); 13C NMR (75.4 MHz, CDCl3) δ 24.4 (C-4), 32.2 (C-7), 37.6 (C-6), 45.7 (C-5), 55.2 (OCH3), 113.4 (CN), 113.7 (CN), 114.5 (C-14), 121.0 (C-3a), 125.1 (C-9), 126.8 (C-11), 127.9 (C-13), 129.3 (C-10), 129.4 (C-12), 130.8 (C-7a), 132.8 (C-8), 153.6 (C-2), 160.3 (C-15); HRMS (EI+) calcd for C22H17N3O3 371.1270, found (M+) 371.1270.
5-(4-Chlorophenyl)-6,6-dicyano-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (9c). According to Method A, the reaction between 5c (0.482 g, 0.0025 mol) and diene 1 (0.400 g, 0.0021 mol), followed by flash column chromatography, afforded 9c (0.60 g, 75%) as a pale yellow solid: mp 179–181 °C; FT-IR (KBr) νmax 2923, 2215, 1778, 1549 cm−1; 1H NMR (300 MHz, CDCl3) δ 2.75 (dd, J = 17.5, 5.0 Hz, 1H, H-4β), 3.01–3.07 (m, 1H, H-4α), 3.42–3.47 (m, 3H, H-5, H-7α, H-7β), 7.35–7.50 (m, 9H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 24.4 (C-4), 29.6 (C-7), 37.2 (C-6), 46.1 (C-5), 113.1 (CN), 113.4 (CN), 120.8 (C-3a), 125.3 (C-9), 127.9 (C-7a), 128.6 (C-11), 129.7, 129.7, 129.8, 129.9 (C-10, C-13, C-14), 132.8 (C-8), 133.3 (C-15), 136.0 (C-12), 153.6 (C-2); HRMS (EI+) calcd for C21H14ClN3O2 375.0774, found (M+) 375.0774.
6,6-Dicyano-5-(4-nitrophenyl)-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (9d). According to Method A, the reaction between 5d (0.383 g, 0.0019 mol) and diene 1 (0.300 g, 0.0016 mol) followed by flash column chromatography, afforded 9d (0.525 g, 85%) as a pale yellow solid: mp 166–167 °C; FT-IR (KBr) νmax 2918, 2220, 1772, 1599 cm−1; 1H NMR (300 MHz, CDCl3) δ 2.80 (dd, J = 17.7, 5.1 Hz, 1H, H-4β), 3.01–3.16 (m, 1H, H-4α), 3.45–3.50 (m, 2H, H-7α, H-7β), 3.60 (dd, J = 10.5, 5.1 Hz, 1H, H-5), 7.30–7.55 (m, 5H, H-Ar), 7.62 (d, J = 8.5 Hz, 2H, H-13), 8.30 (d, J = 8.5 Hz, 2H, H-14); 13C NMR (75.4 MHz, CDCl3) δ 24.3 (C-4), 32.6 (C-7), 36.8 (C-6), 46.3 (C-5), 113.0 (CN), 113.3 (CN), 120.5 (C-3a), 124.5 (C-14), 125.3 (C-9), 127.8 (C-7a), 128.8 (C-11), 129.4 (C-13), 129.9 (C-10), 133.0 (C-8), 141.5 (C-12), 149.0 (C-15), 153.0 (C-2); HRMS (EI+) calcd for C21H14N4O4 386.1015, found (M+) 386.1015.
6,6-Diethoxycarbonyl-3,5-diphenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (11a). According to Method A, the reaction between 6a (0.445 g, 0.0018 mol) and diene 1 (0.280 g, 0.0015 mol), followed by flash column chromatography, afforded 11a (0.243 g, 35%) as a white solid: mp 124–125 °C; FT-IR (KBr) νmax 2926, 1770, 1732, 1502 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.16 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.20 (t, J = 6.9 Hz, 3H, OCH2CH3), 2.58 (d, J = 16.8 Hz, 1H, H-4α), 3.11 (ddd, J = 16.8, 3.9, 2.4 Hz, 1H, H-7β), 3.22–3.32 (m, 2H, H-4α, H-7α), 3.94 (dd, J = 7.2, 2.4 Hz, 1H, H-5), 4.09 (qd, J = 7.2, 4.8 Hz, 2H, OCH2CH3), 4.19 (qd, J = 6.9, 4.8 Hz, 2H, OCH2CH3), 7.13–7.45 (m, 10H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (OCH2CH3), 13.8 (OCH2CH3), 24.5 (C-4), 25.4 (C-7), 42.5 (C-5), 58.3 (C-6), 61.8 (OCH2CH3), 62.1 (OCH2CH3), 120.2 (C-3a), 125.1 (C-13), 127.8 (C-11), 127.8 (C-15), 128.0 (C-10), 128.7 (C-9), 129.4 (C-14), 132.1 (C-7a), 133.6 (C-8), 139.8 (C-12), 154.5 (C-2), 168.3 (CO2CH2CH3), 169.5 (CO2CH2CH3); HRMS (EI+) calcd for C25H25NO6 435.1681, found (M+) 435.1681.
6,6-Diethoxycarbonyl-5-(4-methoxyphenyl)-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (11b). According to Method A, the reaction between 6b (0.624 g, 0.0022 mol) and diene 1 (0.350 g, 0.0018 mol), followed by flash column chromatography, afforded 11b (0.215 g, 25%) as a white solid: mp 140–141 °C; FT-IR (KBr) νmax 2929 1769, 1729, 1504 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.20–1.23 (m, 6H, OCH2CH3), 2.85 (d, J = 16.8, 1H, H-4α), 3.11 (ddd, J = 16.8, 3.6, 2.2 Hz, 1H, H-7β), 3.23–3.32 (m, 2H, H-4β, H-7α), 3.48–3.56 (m, 1H, H-5), 3.76 (s, 3H, OCH3), 4.08–4.18 (m, 4H, OCH2CH3), 6.78 (d, J = 9.0 Hz, 2H, H-13), 7.07 (d, J = 9.0 Hz, 2H, H-14), 7.31–7.42 (m, 5H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (OCH2CH3), 13.9 (OCH2CH3), 24.8 (C-7), 25.4 (C-4), 42.5 (C-5), 55.1 (C-6), 61.8 (OCH2CH3), 62.1 (OCH2CH3), 113.8 (C-14), 120.2 (C-3a), 125.1 (C-9), 127.8 (C-11), 129.0 (C-13), 129.4 (C-12), 131.8 (C-10), 132.1 (C-7a), 154.4 (C-2), 159.0 (C-15), 168.5 (CO2CH2CH3), 169.5 (CO2CH2CH3); HRMS (EI+) calcd for C26H27NO7 465.1787, found (M+) 465.1787.
5-(4-Chlorophenyl)-6,6-diethoxycarbonyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (11c). According to Method A, the reaction between 6c (0.542 g, 0.0019 mol) and diene 1 (0.300 g, 0.0016 mol), followed by flash column chromatography, afforded 11c (0.225 g, 30%) as a white solid: mp 167–169 °C; FT-IR (KBr) νmax 2981, 1770, 1732, 1503 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.18 (t, J = 7.5 Hz, 3H, OCH2CH3), 1.19 (t, J = 7.5 Hz, 3H, OCH2CH3), 2.57 (dd, J = 17.1, 2.4 Hz, 1H, H-4α), 3.08 (ddd, J = 17.1, 3.3, 2.4 Hz, 1H, H-7β), 3.18–3.30 (m, 2H, H-4β, H-7α), 3.90 (dd, J = 6.9, 2.4 Hz, 1H, H-5), 4.05–4.21 (m, 2H, OCH2CH3), 7.10 (d, J = 8.7 Hz, 2H, H-13), 7.24 (d, J = 8.7 Hz, 2H, H-14), 7.30–7.46 (m, 5H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (OCH2CH3), 13.9 (OCH2CH3), 24.8 (C-7), 25.4 (C-4), 42.2 (C-5), 58.2 (C-6), 61.9 (OCH2CH3), 62.2 (OCH2CH3), 120.0 (C-3a), 125.1 (C-9), 127.9 (C-11), 128.8 (C-14), 129.4 (C-13), 129.5 (C-10), 132.0 (C-15), 133.7 (C-7a), 138.3 (C-12), 154.4 (C-2), 168.2 (CO2CH2CH3), 169.3 (CO2CH2CH3); HRMS (EI+) calcd for C25H24NO6Cl 469.1292, found (M+) 469.1292.
(5R*,6S*,7R*)-6-Cyano-6-ethoxycarbonyl-7-methyl-3,5-diphenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (13a). (5R*,6S*,7S*)-6-Cyano-6-ethoxycarbonyl-7-methyl-3,5-diphenyl-4,5,6,7-tetrahydrobenzo [d]oxazol-2-one (14a). According to Method A, the reaction between 4a (0.480 g, 0.0023 mol) and diene 2 (0.400 g, 0.0020 mol) gave a mixture of isomers 13a/14a (80:20) as a white solid. The isomers were separated by flash column chromatography, giving 0.450 g (56%) of 13a as white solid, mp 165–166 °C and 0.250 g (32%) of 14a as a pale yellow solid, mp 165–167 °C. Data of 13a: FT-IR (KBr) νmax 2984, 2362, 1769, 1750, 1500 cm−1; 1H NMR (500 MHz, CDCl3) δ 1.11 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.35 (d, J = 6.9 Hz, 3H, H-16), 2.62 (dd, J = 17.1, 5.4 Hz, 1H, H-4β), 2.93 (ddd, J = 17.1, 11.1, 1.8 Hz, 1H, H-4α), 3.49–3.54 (m, 2H, H-5, H-7), 4.09 (q, J = 7.2 Hz, 2H, OCH2CH3), 7.26–7.51 (m, 10H, H-Ar); 13C NMR (125 MHz, CDCl3) δ 13.7 (OCH2CH3), 15.9 (C-16), 27.0 (C-4), 37.0 (C-7), 40.4 (C-5), 52.2 (C-6), 62.9 (OCH2CH3), 118.2 (CN), 120.0 (C-3a), 125.2 (C-9), 128.1 (C-11), 128.2 (C-15), 128.4 (C-14), 128.7 (C-13), 129.6 (C-10), 133.3 (C-7a), 134.6 (C-8), 138.0 (C-12), 154.0 (C-2), 164.7 (CO2CH2CH3); Data of 14a. FT-IR (KBr) νmax 2984, 2262, 1769, 1750, cm−1; 1H NMR (500 MHz, CDCl3) δ 0.86 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.42 (d, J = 6.9 Hz, 3H, H-16), 3.13 (ddd, J = 17.1, 11.7, 4.5 Hz, 1H, H-4α), 3.48–3.53 (m, 2H, H-5, H-7), 3.95 (q, J = 7.2 Hz, 2H, OCH2CH3), 7.24–7.58 (m, 10H, H-Ar); 13C NMR (125 MHz, CDCl3) δ 13.4 (OCH2CH3), 15.7 (C-16), 26.8 (C-4), 36.4 (C-7), 154.1 (C-2); HRMS (EI+) calcd for C24H22N2O4 402.1579, found (M+) 402.1580.
Method B. Reaction of ethyl 2-cyanoacetate 20a (0.200 g, 0.0017 mol), benzaldehyde 21a (0.184 g, 0.0017 mol) with exo-2-oxazolidinone diene 2 (0.350 g, 0.0017 mol) gave a mixture of isomers 13a/14a (65:35). The isomers were separated by flash column chromatography, giving 0.340 g (43%) of 13a and 0.095 g (12%) of 14a.
(5R*,6S*,7R*)-6-Cyano-6-ethoxycarbonyl-5-(4-methoxyphenyl)-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (13b). (5R*,6S*,7S*)-6-Cyano-6-ethoxycarbonyl-5-(4-methoxyphenyl)-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (14b). According to Method A, the reaction between 4b (0.480 g, 0.0020 mol) and diene 2 (0.350 g, 0.0017 mol) gave a mixture of isomers 13b/14b (75:25) as a pale yellow solid, which was purified by flash column chromatography, to yield 0.520 g (65%) of major isomer 13b as pale yellow solid: mp 172–174 °C. Data of 13b: FT-IR (KBr) νmax 2933, 2200, 1767, 1754, 1501 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.14 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.37 (d, J = 6.9 Hz, 3H, H-16), 2.59 (dd, J = 17.1, 4.8 Hz, 1H, H-4β), 2.86–2.95 (m, 1H, H-4α), 3.46–3.51 (m, 2H, H-5, H-7), 3.83 (s, 3H, OCH3), 4.09 (q, J = 7.2 Hz, 2H, OCH2CH3), 6.84 (d, J = 8.7 Hz, 2H, H-14), 7.27–7.47 (m, 7H, H-Ar). Signals attributed to minor isomer 14b: 0.92 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.42 (d, J = 6.9 Hz, 3H, H-16), 2.38 (dd, J = 17.1, 4.8 Hz, 1H, H-4β), 3.08 (dd, J = 16.8, 10.9 Hz, 1H, H-4α), 3.43–3.60 (m, 2H, H-5, H-7), 3.96 (q, J = 7.2 Hz, 2H, OCH2CH3); 13C NMR (75.4 MHz, CDCl3) δ 14.0 (OCH2CH3), 16.2 (C-16), 27.2 (C-7), 31.2 (C-4), 37.1 (C-5), 52.8 (C-6), 55.4 (OCH3), 63.1 (OCH2CH3), 114.2 (C-14), 118.0 (CN), 120.3 (C-3a), 125.4 (C-9), 127.5 (C-11), 129.5 (C-13), 129.8 (C-10), 130.0 (C-8), 133.4 (C-7a), 134.8 (C-12), 152 (C-2), 159.5 (CO2CH2CH3), 165.0 (C-15); HRMS (EI+) calcd for C25H24N2O5 432.1685, found (M+). 432.1681.
Method B. Reaction of ethyl 2-cyanoacetate 20a (0.190 g, 0.0017 mol) and benzaldehyde 21b (0.230 g, 0.0017 mol) with exo-2-oxazolidinone diene 2 (0.350 g, 0.0017 mol) gave a mixture of isomers 13b/14b (75:25). The isomers were separated by flash column chromatography, giving 0.300 g (40%) of major isomer 13b.
(5R*,6S*,7R*)-5-(4-Chlorophenyl)-6-cyano-6-ethoxycarbonyl-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (13c). (5R*,6S*,7S*)-5-(4-Chlorophenyl)-6-cyano-6-ethoxycarbonyl-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (14c). According to Method A, the reaction between 4c (0.500 g, 0.0020 mol) and diene 2 (0.350 g, 0.0017 mol) gave a mixture of isomers 13c/14c (90:10) as a pale yellow solid, which was purified by flash column chromatography, to yield 0.570 g (75%) of major isomer 13c as pale yellow solid: mp 182–184 °C. Data of 13c: FT-IR (KBr) νmax 2931, 2230, 1773, 1719, 1544 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.16 (t, J = 6.9 Hz, 3H, OCH2CH3), 1.33 (d, J = 6.9 Hz, 3H, H-16), 2.58 (dd, J = 16.8, 5.1 Hz, 1H, H-4β), 2.89 (ddd, J = 16.8, 11.1, 1.6 Hz, 1H, H-4α), 3.46–3.54 (m, 2H, H-5, H-7), 4.11 (qd, J = 6.9, 1.5 Hz, 2H, OCH2CH3), 7.28–7.47 (m, 9H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.7 (OCH2CH3), 15.8 (C-16), 27.0 (C-4), 37.0 (C-7), 40.1 (C-5), 52.2 (C-6), 62.9 (OCH2CH3), 118.2 (CN), 120.0 (C-3a), 125.2 (C-9), 128.1 (C-10), 128.4 (C-11), 129.4 (C-13), 129.6 (C-14), 133.2 (C-8), 134.5 (C-7a), 146.0 (C-12), 148.0 (C-15), 154.0 (C-2), 164.2 (CO2CH2CH3); HRMS (EI+) calcd for C24H21N2O4Cl 436.1190, found (M+) 436.1186.
Method B. Reaction of ethyl 2-cyanoacetate 20a (0.17 g, 0.0015 mol) and benzaldehyde 21c (0.200 g, 0.0015 mol) with exo-2-oxazolidinone diene 2 (0.300 g, 0.0015 mol) gave a mixture of isomers 13c/14c (68:32). The isomers were separated by flash column chromatography, giving 0.456 g (64%) of major isomer 13c.
(5R*,6S*,7R*)-6-Cyano-6-ethoxycarbonyl-7-methyl-5-(4-nitrophenyl)-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (13d). (5R*,6S*,7S*)-6-Cyano-6-ethoxycarbonyl-7-methyl-5-(4-nitrophenyl)-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (14d). According to Method A, the reaction between 4d (0.513 g, 0.0020 mol) and diene 2 (0.350 g, 0.0017 mol) gave a mixture of isomers 13d/14d (85:15) as a pale yellow solid, which was purified by flash column chromatography, to yield 0.660 g (80%) of major isomer 13d as white solid: mp 178–180 °C. Data of 13d: FT-IR (KBr) νmax 3078, 2983, 2240, 1764, 1710, 1520 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.19 (t, J = 6.9 Hz, 3H, OCH2CH3), 1.34 (d, J = 7.0 Hz, 3H, H-16), 2.64 (dd, J = 16.5, 4.8 Hz, 1H, H-4β), 2.94 (ddd, J = 16.5, 11.4, 1.5 Hz, 1H, H-4α), 3.56–3.67 (m, 2H, H-5, H-7), 4.14 (qdd, J = 6.9, 4.5, 2.7 Hz, 2H, OCH2CH3), 7.37–7.45 (m, 5H, H-Ar), 7.71 (d, J = 8.7 Hz, 2H, H-13), 8.19 (d, J = 8.7 Hz, 2H, H-14). Signals attributed to minor isomer 14d: 0.95 (t, J = 6.9 Hz, 3H, OCH2CH3), 1.47 (d, J = 7.0 Hz, 3H, H-16), 3.12 (ddd, J = 16.5, 11.4, 1.5 Hz, 1H, H-4α), 3.99 (qdd, J = 6.9, 4.5, 2.7 Hz, 2H, OCH2CH3); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (OCH2CH3), 15.7 (C-16), 26.7 (C-4), 37.0 (C-7), 40.0 (C-5), 51.7 (C-6), 63.4 (OCH2CH3), 117.6 (CN), 119.4 (C-3a), 123.7 (C-9), 125.2 (C-10), 128.3 (C-11), 129.4 (C-13), 129.6 (C-14), 133.0 (C-8), 133.1 (C-7a), 134.3 (C-12), 147.6 (C-15), 153.8 (C-2), 164.4 (CO2CH2CH3); HRMS (EI+) calcd for C24H21N3O6 447.1430, found (M+). 447.1450.
Method B. Reaction of ethyl 2-cyanoacetate 20a (0.17 g, 0.0015 mol) and benzaldehyde 21d (0.220 g, 0.0015 mol) with exo-2-oxazolidinone diene 2 (0.300 g, 0.0015 mol) gave a mixture of isomers 13d/14d (75:25). The isomers were separated by flash column chromatography, giving 0.419 g (64%) of major isomer 13d.
(5R*,6S*,7R*)-3-(4-Chlorophenyl)-6-cyano-6-ethoxycarbonyl-7-methyl-5-(3-nitrophenyl)-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (13e). (5R*,6S*,7S*)-3-(4-Chlorophenyl)-6-cyano-6-ethoxycarbonyl-7-methyl-5-(3-nitrophenyl)-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (14e). According to Method A, the reaction between 4e (0.280 g, 0.0015 mol) and diene 3 (0.300 g, 0.0012 mol) gave a mixture of isomers 13e/14e (75:25) as a pale yellow solid, which was purified by flash column chromatography, to yield 0.430 g (70%) 13e as a pale yellow solid: mp 180–182 °C; FT-IR (KBr) νmax 2926, 2230, 1772, 1749, 1529 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.19 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.34 (d, J = 6.9 Hz, 3H, H-16), 2.67 (dd, J = 17.2, 5.4 Hz, 1H, H-4β), 2.95 (ddd, J = 17.2, 11.1, 1.8 Hz, 1H, H-4α), 3.57 (q, J = 6.9 Hz, 1H, H-7), 3.65 (dd, J = 11.1, 5.4 Hz, 1H, H-5), 4.13 (q, J = 7.2 Hz, 2H, OCH2CH3), 7.33 (d, J = 8.7 Hz, 2H, H-9), 7.43 (d, J = 8.7 Hz, 2H, H-10), 7.55 (t, J = 8.1 Hz, 1H, H-17), 7.91 (d, J = 8.1 Hz, 1H, H-18), 8.18 (d, J = 8.4, 3 Hz, 1H, H-15), 8.36 (dd, J = 1.8, 1.2 Hz, 1H, H-13). Signals attributed to minor isomer 14e: 0.92 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.42 (d, J = 6.9 Hz, 3H, H-16), 3.17 (ddd, J = 17.1, 11.1, 1.8 Hz, 1H, H-4α), 4.02 (qd, J = 7.2, 2.1 Hz, 2H, OCH2CH3), 7.82 (d, J = 8.1 Hz, 1H, H-17), 8.21 (d, J = 8.4 Hz, 1H, H-15); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (OCH2CH3), 15.8 (C-16), 26.7 (C-4), 36.9 (C-7), 39.9 (C-5), 51.8 (C-6), 63.4 (OCH2CH3), 117.5 (CN), 119.2 (C-3a), 123.3 (C-11), 124.3 (C-17), 126.4 (C-13), 129.9 (C-10), 134.0 (C-8), 134.1 (C-9), 134.7 (C-15), 139.9 (C-18), 144.0 (C-14), 148.0 (C-2), 164.3 (CO2CH2CH3); HRMS (EI+) calcd for C24H20ClN3O6 481.1040, found (M+) 481.1039.
(5R*,7R*)-6,6-Dicyano-7-methyl-3,5-diphenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (15a). (5R*,7S*)-6,6-Dicyano-7-methyl-3,5-diphenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (16a). According to Method A, the reaction between 5a (0.386 g, 0.0025 mol) and diene 2 (0.420 g, 0.0020 mol) gave a mixture of isomers 15a/16a (80:20) as a pale yellow solid, which was purified by flash column chromatography, to yield 0.520 g (70%) of major isomer 15a as pale yellow solid: mp 145–147 °C. Data of 15a: FT-IR (KBr) νmax 2979, 2210, 2215, 1777, 1523 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.71 (d, J = 7.2 Hz, 3H, H-16), 2.70 (ddd, J = 17.1, 4.8, 2.1 Hz, 1H, H-4β), 3.14 (ddd, J = 17.1, 11.4, 4.0 Hz, 1H, H-4α), 3.48 (dd, J = 11.4, 4.8 Hz, 1H, H-5), 3.54–3.58 (m, 1H, H-7), 7.35–7.50 (m, 10H, H-Ar). Signals attributed to minor isomer 16a: 1.67 (d, J = 7.2 Hz, 3H, H-16); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (C-16), 24.8 (C-4), 38.6 (C-7), 45.7 (C-6), 47.6 (C-5), 112.0 (CN), 113.5 (CN), 120.7 (C-3a), 125.2 (C-9),128.0 (C-11), 128.5 C (15), 129.4 (C-14), 129.7 (C-13), 129.8 (C-10), 131.9 (C-7a), 132.2 (C-12), 135.3 (C-8), 154.0 (C-2); HRMS (EI+) calcd for C22H17N3O2 355.1320, found (M+) 355.1319.
Method B. Reaction of malononitrile 20b (0.114 g, 0.0017 mol) and benzaldehyde 21a (0.184 g, 0.0017 mol) with exo-2-oxazolidinone diene 2 (0.350 g, 0.0017 mol) gave a mixture of isomers 15a/16a (70:30). The isomers were separated by flash column chromatography, giving 0.340 g (55%) of major isomer 15a.
(5R*,7R*)-6,6-Dicyano-5-(4-methoxyphenyl)-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (15b). (5R*,7R*)-6,6-Dicyano-5-(4-methoxyphenyl)-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo [d]oxazol-2-one (16b). According to Method A, the reaction between 5b (0.60 g, 0.0030 mol) and diene 2 (0.500 g, 0.0024 mol) gave a mixture of isomers 15b/16b (82:18) as a pale yellow solid, which was purified by flash column chromatography, to yield 0.528 g (55%) of major isomer 15b as pale yellow solid: mp 150–152 °C. Data of 15b: FT-IR(KBr) νmax 2977, 2936, 2235, 2230, 1776, 1597, cm−1; 1H NMR (300 MHz, CDCl3) δ 1.68 (d, J = 7.2 Hz, 3H, H-16), 2.66 (ddd, J = 17.1, 4.8, 2.1 Hz, 1H, H-4β), 3.08 (ddd, J = 17.1, 11.4, 3.9 Hz, 1H, H-4α), 3.47 (dd, J = 11.4, 4.8 Hz, 1H, H-5) 3.52 (qdd, J = 7.2, 3.9, 2.1 Hz, 1H, H-7), 3.80 (s, 3H, OCH3), 6.92 (d, J = 8.7 Hz, 2H, H-14), 7.34–7.48 (m, 7H, H-9, H-10, H-11, H-13). Signals attributed to minor isomer 16b: 1.67 (d, J = 7.2 Hz, 3H, H-16); 13C NMR (75.4 MHz, CDCl3) δ 13.8 (C-16), 24.7 (C-4), 38.3 (C-7), 46.1 (C-6), 46.7 (C-5), 55.2 (OCH3), 111.8 (CN), 113.4 (CN),114.5 (C-14), 120.4 (C-3a), 125.2 (C-9), 127.2 (C-12), 128.4 (C-11), 129.3 (C-13), 129.7 (C-10), 132.0 (C-7a), 132.9 (C-8), 153.7 (C-2), 160.3 (C-15); HRMS (EI+) calcd for C23H19N3O3 385.1426, found (M+) 385.1411.
Method B. Reaction of malononitrile 20b (0.114 g, 0.0017 mol) and benzaldehyde 21b (0.236 g, 0.0017 mol) with exo-2-oxazolidinone diene 2 (0.350 g, 0.0017 mol) gave a mixture of isomers 15b/16b (85:15). The isomers were separated by flash column chromatography, giving 0.478 g (50%) of major isomer 15b.
(5R*,7R*)-5-(4-Chlorophenyl)-6,6-dicyano-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (15c). (5R*,7S*)-5-(4-Chlorophenyl)-6,6-dicyano-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d] oxazol-2-one (16c). According to Method A, the reaction between 5c (0.336 g, 0.0017 mol) and diene 2 (0.300g, 0.0015 mol) gave a mixture of isomers 15c/16c (90:10) as a pale yellow solid, which was purified by flash column chromatography, to yield 0.435 g (75%) of major isomer 15c as pale yellow solid: mp 172–173 °C. Data of 15c: FT-IR (KBr) νmax 2926, 2230, 1754, 1520 cm−1; 1H NMR (500 MHz, CDCl3) δ 1.62 (d, J = 6.9 Hz, 3H, H-16), 2.94 (dd, J = 8.5, 3.0 Hz, 1H, H-4β), 3.31 (ddd, J = 17.1, 11.4, 3.9, Hz, 1H, H-4α), 3.91–3.99 (m, 1H, H-7), 4.03 (dd, J = 11.4, 5.1 Hz, 1H, H-5), 7.40–7.66 (m, 9H, H-Ar). Signals attributed to minor isomer 16c; 13C NMR (125 MHz, CDCl3) δ 14.5 (C-16), 24.3 (C-4), 38.6 (C-7), 43.2 (C-5), 47.3 (C-6), 112.1 (CN), 113.0 (CN), 125.7 (C-9), 128.2 (C-14), 128.4 (C-11), 129.0 (C-13), 130.3, (C-10), 131.0 (C-15), 132.0 (C-7a), 133.4 (C-8), 134.0 (C-12), 154.0 (C-2); HRMS (EI+) calcd for C22H16N3O2Cl 389.0931, found (M+) 389.0901.
Method B. Reaction of malononitrile 20b (0.131 g, 0.0019 mol) and benzaldehyde 21c (0.027 g, 0.0019 mol) with exo-2-oxazolidinone diene 2 (0.400 g, 0.0019 mol) gave a mixture of isomers 15c/16c (70:30). The isomers were separated by flash column chromatography, giving 0.425 g (55%) of 15c and 0.11 g (15%) of 16c.
(5R*,7R*)-6,6-Dicyano-7-methyl-5-(4-nitrophenyl)-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (15d). (5R*,7S*)-6,6-Dicyano-7-methyl-5-(4-nitrophenyl)-3-phenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (16d). According to Method A, the reaction between 5d (0.53 g, 0.0026 mol) and diene 2 (0.450 g, 0.0022 mol) gave a mixture of isomers 15d/16d (80:20) as a pale yellow solid. The isomers were separated by flash column chromatography, giving 0.670 g (75%) of 15d as pale yellow solid, mp 169–171 °C and 0.134 g (15%) of 16d as a pale yellow solid, mp 170–171 °C. Data of 16d: FT-IR (KBr) νmax 2925, 2215, 1772, 1599, cm−1; 1H NMR (300 MHz, CDCl3) δ 1.66 (d, J = 6.9 Hz, 3H, H-16), 3.03 (ddd, J = 16.8, 4.8, 2.1 Hz, 1H, H-4β), 3.41 (ddd, J = 16.8, 11.4, 3.9 Hz, 1H, H-4α), 3.92–4.01 (m, 1H, H-7), 4.27 (dd, J = 11.4, 4.8 Hz, 1H, H-5), 7.48–7.57 (m, 5H, H-9, H-10, H-11), 7.95 (d, J = 8.9 Hz, 2H, H-13), 8.35 (d, J = 8.9 Hz, 2H, H-14). Signals attributed to minor isomer 16d: 1.61 (d, J = 6.9 Hz, 3H, H-16), 3.09 (ddd, J = 16.8, 4.8, 2.1 Hz, 1H, H-4β), 3.29 (ddd, J = 16.8, 11.4, 3.9 Hz, 1H, H-4α), 3.81–3.84 (m, 1H, H-7), 4.24 (dd, J = 8.4, 4.8 Hz, 1H, H-5); 13C NMR (75.4 MHz, DMSO-d6) δ 13.9 (C-16), 24.6 (C-4), 38.2 (C-7), 46.0 (C-6), 46.5 (C-5), 112.8 (CN), 114.2 (CN), 121.2 (C-3a), 124.7 (C-14), 126.1 (C-9), 128.7 (C-11), 128.8 (C-10), 130.1 (C-13), 132.5 (C-7a), 131.1 (C-8), 134.4(C-12), 144.5 (C-8), 149.2 (C-15), 154.0 (C-2); HRMS (EI+) calcd for C22H16N4O4 400.1171, found (M+) 400.1165.
Method B. Reaction of malononitrile 20b (0.170 g, 0.0015 mol) and benzaldehyde 21d (0.300 g, 0.0019 mol) with exo-2-oxazolidinone diene 2 (0.300 g, 0.0019 mol) gave a mixture of isomers 15d/16d (70:30). The isomers were separated by flash column chromatography, giving 0.431 g (55%) of 15d and 0.165 g (15%) of 16d.
(5R*,7R*)-3-(4-Chlorophenyl)-6,6-dicyano-5-(4-methoxyphenyl)-7-methyl-4,5,6,7-tetrahydrobenzo [d]oxazol-2-one (15e). (5R*,7S*)-3-(4-Chlorophenyl)-6,6-dicyano-5-(4-methoxyphenyl)-7-methyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (16e). According to Method A, the reaction between 5b (0.280 g, 0.0015 mol) and diene 3 (0.300 g, 0.0012 mol) gave a mixture of isomers 15e/16e (75:25) as a pale yellow solid. The isomers were separated by flash column chromatography, giving 0.387 g (70%) of 15e as pale yellow solid, mp 162–163 °C and 0.083 g (15%) of 16e as a pale yellow solid, mp 162–163 °C. Data of 15e: FT-IR (KBr) νmax 2935, 2250, 1760, 1496 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.67 (d, J = 6.6 Hz, 3H, H-16), 2.69 (ddd, J = 17.4, 5.1, 2.1 Hz, 1H, H-4β), 3.09 (ddd, J = 17.4, 11.7, 3.9 Hz, 1H, H-4α), 3.45 (dd, J = 10.8, 5.1 Hz,1H, H-5), 3.47–3.82 (m, 1H, H-7), 3.82 (s, 3H, OCH3), 6.96 (d, J = 9.0 Hz, 2H, H-14), 7.33 (d, J = 9.0 Hz, 4H, H-13, H-9), 7.40 (d, J = 9.0 Hz, 2H, H-9), 7.46 (d, J = 9.0 Hz, 2H, H-10); 13C NMR (75.4 MHz, CDCl3) δ 14.1 (C-16), 25.1 (C-4), 38.7 (C-7), 46.3 (C-6), 47.1 (C-5), 55.6 (OCH3), 112.1 (CN), 113.6 (CN), 114.9 (C-14), 120.4 (C-3a), 126.7 (C-9), 127.3 (C-12), 129.5 (C-13), 130.2 (C-10), 131.7 (C-8), 132.5 (C-7a), 134.6 (C-11), 153.7 (C-2), 160.5 (C-15). Data of 16e. Yield: 57% (pale yellow solid, mp 163–165 °C); FT-IR (KBr) νmax 2935, 2235, 1760, 1609 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.63 (d, J = 6.9 Hz, 3H, H-16), 2.83–2.98 (m, 2H, H-4), 3.37–3.39 (m, 1H, H-7), 3.54–3.57 (m, 1H, H-5), 3.82 (s, 3H, OCH3), 6.94 (d, J = 8.7 Hz, 2H, H-14), 7.31 (d, J = 8.7 Hz, 4H, H-13, H-9), 7.45 (d, J = 9.0 Hz, 2H, H-10); 13C NMR (75.4 MHz, CDCl3) δ 15.1 (C-16), 24.5 (C-4), 35.1 (C-7), 42.3 (C-6), 43.3 (C-5), 55.3 (OCH3), 112.8 (CN), 113.6 (CN), 114.6 (C-14), 119.6 (C-3a), 126.4 (C-12), 126.5 (C-9), 129.4 (C-13), 129.9 (C-10), 131.3 (C-8), 133.0 (C-7a), 134.3 (C-11), 153.4 (C-2), 160.4 (C-15); HRMS (EI+) calcd for C23H18N3O3Cl 419. 1036, found (M+) 419. 1036.
(5R*,7R*)-6,6-Diethoxycarbonyl-7-methyl-3,5-diphenyl-4,5,6,7-tetrahydrobenzo[d]oxazol-2-one (17a). According to Method A, the reaction between 6a (0.44 g, 0.0017 mol) and diene 2 (0.300 g, 0.0015 mol) produced only the isomer 17a (0.154 g, 23%) as pale yellow solid: mp 132–133 °C. FT-IR: νmax 2980, 1770, 1727, 1503 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.18 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.26 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.38 (d, J = 6.9 Hz, 1H, C-16), 2.42 (ddd, J = 17.4, 4.8, 2.1 Hz, H-4α), 3.49–3.59 (m, 2H, H-7, H-4β), 3.82 (dd, J = 6.6, 2.1 Hz, 1H, H-5), 4.04–4.27 (m, 4H, OCH2CH3), 7.23–7.45 (m, 10H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.6 (C-16), 13.8 (OCH2CH3), 14.0 (OCH2CH3), 26.3 (C-7), 29.5 (C-4), 43.3 (C-5), 61.1 (C-6), 61.3 (OCH2CH3), 61.4 (OCH2CH3), 119.5 (C-3a), 125.2 (C-9), 127.7 (C-11), 128.0 (C-12), 128.4 (C-14), 128.6 (C-13), 129.3 (C-10), 133.6 (C-8), 135.1 (C-7a), 154.7 (C-2), 168.5 (CO2CH2CH3) 169.3 (CO2CH2CH3). HRMS (EI+) calcd for C26H27NO6 449.1838, found (M+) 449.1838.
(5R*,7R*)-6,6-Diethoxycarbonyl-5-(4-methoxyphenyl)-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo [d]oxazol-2-one (17b). According to Method A, the reaction between 6b (0.58 g, 0.0028mol) and diene 2 (0.350 g, 0.0017 mol) produced only the isomer 17b (0.269 g, 32%) as a pale yellow solid: mp 143–145 °C. FT-IR: νmax 2980, 1768, 1727, 1504 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.20 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.26 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.37 (d, J = 6.6 Hz, 3H, H-16), 2.38 (ddd, J = 17.1, 4.8, 2.4 Hz, 1H, H-4α), 3.47–3.56 (m, 2H, H-4β, H-7), 3.75 (s, 3H, OCH3), 3.78 (dd, J = 6.9, 2.4 Hz, 1H, H-5), 4.10–4.26 (m, 4H, OCH2CH3), 6.77 (d, J = 8.7 Hz, 2H, H-14), 7.04 (d, J = 8.7 Hz, 2H, H-15), 7.28–7.45 (m, 5H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.6 (C-16), 13.8 (OCH2CH3), 13.9 (OCH2CH3), 26.5 (C-4), 29.5 (C-7), 42.5 (C-5), 55.1 (OCH3), 61.2 (C-6), 61.2 (OCH2CH3), 61.3 (OCH2CH3), 113.8 (C-14), 119.5 (C-3a), 125.2 (C-9), 127.7 (C-11), 129.1 (C-10), 129.3 (C-13), 132.5 (C-12), 133.7 (C-7a), 135.2 (C-8), 154.7 (C-2), 158.9 (C-15), 168.6 (CO2CH2CH3), 169.3 (CO2CH2CH3). HRMS (EI+) calcd for C26H27NO6 479.1944, found (M+) 479.1898.
(5R*,7R*)-5-(4-Chlorophenyl)-6,6-diethoxycarbonyl-7-methyl-3-phenyl-4,5,6,7-tetrahydrobenzo[d] oxazol-2-one (17c). According to Method A, the reaction between 4a (144 mg, 2.0 mmol) and diene 2 (162 mg, 1.0 mmol) produced only the isomer 17c (0.121 g, 25%) as a pale yellow solid: mp 166–168 °C. FT-IR: νmax 2980, 1770, 1729, 1597 cm−1; 1H NMR (300 MHz, CDCl3) δ 1.20 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.25 (t, J = 7.2 Hz, 3H, OCH2CH3), 1.38 (d, J = 6.6 Hz, 1H, H-16), 2.40 (dd, J = 17.4, 2.4 Hz, 1H, H-4α), 3.44–3.52 (m, 2H, H-4β, H-7), 3.80 (dd, J = 6.9, 2.4 Hz, 1H, H-5), 4.08–4.26 (m, 4H, OCH2CH3), 7.09 (d, J = 8.4 Hz, 2H, H-14), 7.22 (d, J = 8.4 Hz, 1H, H-13), 7.31–7.45 (m, 5H, H-Ar); 13C NMR (75.4 MHz, CDCl3) δ 13.7 (C-16), 13.8 (OCH2CH3), 13.8 (OCH2CH3), 29.6 (C-7), 31.4 (C-4), 42.5 (C-5), 60.8 (C-6), 61.4 (OCH2CH3), 61.5 (OCH2CH3), 119.2 (C-3a), 125.0 (C-9), 127.7 (C-11), 128.6 (C-10), 129.3 (C-13), 129.5 (C-14), 130.4 (C-7a), 133.5 (C-15), 135.0 (C-8), 138.8 (C-12), 154.5 (C-2), 168.3 (CO2CH2CH3), 168.9 (CO2CH2CH3). HRMS (EI+) calcd for C26H26NO6Cl 483.1448, found (M+) 483.1445.
Dimerization of Diene 2. According to Method B, the reaction between 20a (0.250 g, 0.0023 mol), 21c (0.375 g, 0.0023 mol) and diene 2 (0.474 g, 0.0023 mol), produced two products: 4a (0.375 g, 64%) and dimer 19 (0.0.340 g, 36%) as a pale yellow crystal (acetone/hexane). 19: mp 196–198 °C; IR (KBr) νmax 2924, 17850, 1762, 1706, 1501, 1245 cm−1; 1H NMR (500 MHz, CDCl3) δ 1.38 (d, J = 6.9 Hz, 3H, H-8), 1.81 (d, 1H, J = 6.9 Hz, 3H, H-14), 2.00–2.10 (m, 1H, H-4β), 2.14–2.20 (m, 1H, H-5β), 2.34–2.41 (m, 1H, H-4α), 2.62–2.75 (m, 1H, H-5α), 2.95–3.08 (m, 1H, H-7α), 4.70 (q, J = 6.9 Hz, 1H, H-13), 7.22–7.48 (m, 10H, H-Ar); 13C NMR (125 MHz, CDCl3) δ 10.2 (C-14), 10.3 (C-8), 17.3 (C-4), 32.2 (C-5), 34.0 (C-7), 67.5 (C-6), 99.5 (C-13), 118.9 (C-3a), 124.9 (C-16), 127.9 (C-20), 128.0 (C-22), 129.5 (C-18), 129.8 (C-21), 130.0 (C-17), 133.0 (C-15), 133.4 (C-19), 134.9 (C-7a), 145.6 (C-12), 154.2 (C-2), 154.3 (C-10); HRMS (EI+) calcd for C24H22N2O4 402.1579, found (M+) 402.1578.