Reaction Steps
A solution of (E)α-nitrochalcone [Dornow et al., Ann., 588:40 (1954); Yamamura et al., Bull. Chem. Soc., Jpn. 44:2440 (1971)] (Compound 7, 5.35 g, 21.1 mmol) in a minimum amount of CH2Cl2 (2-3 mL) was treated with freshly cracked cyclopentadiene (15.7 mL, 190 mmol, 9.0 equiv. ). The reaction mixture was stirred at 45° C. for 24 hours before the mixture was partitioned between CH2Cl2 (200 mL) and H2O (200 mL). The CH2Cl2 layer was dried (Na2SO4) and concentrated under reduced pressure. Chromatography (SiO2, 5×15 cm, 5 percent Et2O-hexane eluant) afforded Compound 9 (5.45 g, 6.73 g theoretical, 81 percent) as a white crystalline solid: mp 119°-120° C. (Et2O-hexane, colorless needles); 1H NMR (CDCl3, 250 MHz) δ 7.33 (d, 2H, J=8.0 Hz), 7.25-6.97 (m, 8H), 6.72 (m, 1H, C6-H), 5.99 (m, 1H, C5-H), 4.24 (d, 1H, J=2.7 Hz, C3-H), 3.84 (s, 1H, C1-H), 2.93 (s, 1H, C4-H), 2.65 (d, 1H, J=9.8 Hz, C7-H syn to ketone), 1.86 (d, 1H, J=9.9 Hz, C7-H anti to ketone); 13C NMR (CDCl3, 62.5 MHz) δ192.5, 144.3, 137.9, 134.2, 133.7, 133.0, 129.0, 128.6, 128.4, 127.9, 127.5, 105.4, 54.8, 53.5, 51.1, 48.5; IR (neat) vmax 3004, 2970, 1685, 1540, 1465, 1354, 1240 cm-1 ; FABHRMS (NBA-NaI) m/e 342.1101 (C20H17NO3 +Na+ requires 342.1106). A mixture of minor diastereomers (<3 percent) was isolated in trace amounts. Anal. Calcd for C20H17NO3 : C, 75.22; H, 5.37; N, 4.39. Found: C, 74.85; H, 5.29; N, 4.55.
