Reaction Steps
To a solution of 20 (0.40 g, 0.86 mmol) in CH2Cl2 (5 mL) was added a mixture of thiourea (0.10 g, 1.3 mmol, 99%) in methanol (5 mL). The resulting mixture was stirred for 24 h at room temperature, after which the solvent was removed under reduced pressure. The residue was partitioned between CH2Cl2 and water. The organic layer was dried over anhydrous Na2SO4 and was filtered. Evaporation of solvent and purification by silica gel chromatography (hexanes/EtOAc=4/1) gave 0.34 g of 21 (83%). 1H NMR (500 MHz, CDCl3) δ 1.53 (s, 9H), 2.14 (dd, J=1.8, 5.0 Hz, 1H), 2.52 (dd, J=1.5, 5.9 Hz, 1H), 3.04 (dq, J=5.6, 7.8 Hz, 1H), 3.15 (dd, J=8.0, 14.2 Hz, 1H), 3.47 (s, 3H), 3.51 (dd, J=5.6, 14.4 Hz, 1H), 5.19 (s, 2H), 6.72 (dd, J=2.6, 8.8 Hz, 1H), 6.91 (d, J=2.6 Hz, 1H), 7.08-7.01 (m, 3H), 7.85-7.80 (m, 2H), 8.16-8.08 (m, 1H). 13C NMR (126 MHz, CDCl3) δ 24.4, 26.2, 28.5, 56.6, 62.7, 80.8, 95.3, 107.3, 114.1, 117.3, 119.4, 126.2, 130.8, 131.6, 146.6, 149.3, 152.8, 163.5. HRMS (FAB) calcd for C22H28NO7S2 (M+H+) 482.1302. found 482.1301.
