Reaction Steps
A mixture of diol 20 (26 g, 64.6 mmol, 1.0 equiv.) and SnCl2.2H2O (72.9 g, 323 mmol, 5.0 equiv.) in MeOH (300 mL), was heated at reflux and the progress of the reaction monitored by TLC (EtOAc). After 3 h, the MeOH was evaporated in vacuo and the resulting residue was cooled and treated carefully with saturated NaHCO3 (400 mL). The mixture was diluted with EtOAc (800 mL), and after 12 h stirring at room temperature the inorganic precipitate was removed by filtration through celite. The organic layer was separated, washed with brine (100 mL), dried (MgSO4), filtered and evaporated in vacuo to give a brown solid 21 which was used in the next reaction without further purification: [α]29D=−69° (c=0.13, CHCl3); 1H NMR (CDCl3, 400 MHz): δ 1.70-1.82 (m, 1H, 1-H), 2.06-2.19 (m, 1H, 1-H), 3.52-3.85 (m, 9H, 3-H, 11-H, 7-OMe, 2×OH), 4.26-4.72 (m, 1H, 11a-H), 4.47-4.60 (m, 1H, 2-H), 5.10 (s, 2H, OCH2Ph), 6.26 (s, 1H, 9-H), 6.78 (s, 1H, 6-H), 7.29-7.36 (m, 7H, Ph, NH2); 13C NMR (CDCl3, 100 MHz): δ 37.0, 57.1, 58.5, 59.0, 66.2, 69.4, 70.7, 103.4, 112.4, 112.9, 127.1, 128.0, 128.6, 136.5, 140.0, 141.9, 151.0, 172.8; IR (neat): 3358, 2939, 1619, 1589, 1512, 1455, 1432, 1408, 1263, 1231, 1171, 1113, 1012, 787, 735, 698, 644 cm−1; MS (ES+) m/z (relative intensity) 395 ([M+Na]+., 4), 373 ([M+H]+., 70), 374 ([M+2H]+., 40), 256 (100), 257 (45).
