Reaction Steps
Powdered compound 13 (427 mg, 0.98 mmol) was added in several portions to 50 mL of cold concentrated sulfuric acid (50 mL) at -40° C. under nitrogen with vigorous mechanical stirring. After the addition, the reaction mixture was warmed to -5° C. over 2 h and then poured onto crushed ice (450 g) and left stirring for 1 h. The product was extracted with dichloromethane (2×150 mL), washed with water (2×150 mL ), dried (MgSO4), filtered and evaporated to afford an oil that on trituration with ether at 0° C. yielded compound 14 (353 mg, 82%) as a white solid that was used for the next step without further purification. An analytical sample was prepared by centrifugal rotary chromatography using 50% ethyl acetate-hexane as the eluent followed by recrystallization from EtOAc/Hexane: mp 204-206° C.; 1H NMR (CDCl3) δ2.40 (s, 3H, CH3), 2.80 (m, 1H, H-1a), 3.50 (dd, 1H, J=4.5, 17.5 Hz, H-1b), 3.70 (dd, 1H, J=7, 14 Hz, H-3a), 3.828 (s, 3H, OCH3), 3.832 (s, 3H, OCH3), 3.9 (m, 1H, H-11b), 4.31 (d, 1H, J=17.6 Hz, H-7a), 4.74 (ddd, 1H, J=1.7, 6.0, 11.2 Hz, H-7b), 4.76 (d, 1H, J=14.8 Hz, H-3b), 6.77 (d, 1H, J=8.3 Hz, ArH), 6.87 (d, 1H, J=8.4 Hz, ArH), 6.94 (d, 1H, J=7.6 Hz, ArH), 7.13 (t, 1H, J=7.5 Hz, Ar-H-5), 7.18 (d, 1H, J=7.2 Hz, ArH), 7.33 (d, 2H, J=8.1 Hz, ArH), 7.78 (d, 2H, J=8.2 Hz, ArH); MS (CI) m/z 436 (55), 198 (86), 157 (100); HRCIMS Calculated for C25H25NO4S: 436.1583; Found 436.1570; Anal. (C25H25NO4S) C, H, N.
