A mixture of 8a (0.20 g, 0.51 mmol), diphenyl-2-pyridylphosphine (0.20 g, 0.77 mmol) and acetic acid (0.12 mL, 2.05 mmol) was dissolved in anhydrous THF (15 mL) under an argon atmosphere. To this solution was added di-tert-butylazodicarboxylate (DBAD) (0.18 g, 0.77 mmol) in one portion and the mixture was stirred for 18 hours at 60° C. The solvent was under reduced pressure and the residue was dissolved in dichloromethane (25 mL). The CH2Cl2 portion was washed with 4 M HCl (2×25 mL) and saturated NaCl (25 mL), and dried (Na2SO4). Removal of the solvent under reduced pressure afforded a crude residue. Flash column chromatography (eluent: n-hexanes/EtOAc, 7:3) gave 0.18 g (80%) of 34 as a white crystalline solid, mp 215-216° C.; 1H NMR (CDCl3): δ 1.10 (3H, s); 1.28 (1H, dd, J=6.0, 14.1); 1.45 (1H, m); 1.46 (3H, s); 1.64 (2H, m); 1.80 (1H, dd, J=3.0, 9.9); 2.10 (1H, m); 2.13 (3H, s); 2.18 (1H, ddd, J=3.3, 3.3, 15.0); 2.34 (1H, ddd, J=3.3, 13.0, 15.6); 2.45 (1H, dd, J=5.1, 13.5); 2.54 (1H, s); 2.90 (1H, dd, J=3.6, 13.2); 3.71 (3H, s); 4.85 (1H, dd, J=3.2, 3.2); 5.54 (1H, dd, J=5.1, 11.7); 6.38 (1H, dd, J=1.4, 1.7); 7.40 (2H, m); 13C NMR (CDCl3): δ 15.4, 16.3, 18.3, 21.2, 31.1, 35.2, 38.8, 43.2, 43.6, 51.1, 51.5, 52.1, 61.9, 72.3, 76.6, 108.5, 125.7, 139.4, 143.9, 169.6, 171.4, 172.4, 204.6; anal. C 63.63%, H 6.59%, O 29.70%, calcd for C25H28N2O7S, C 63.88%, H 6.53%, O 29.60%.
