Reaction Steps
A similar procedure (Hursthouse, M. B.; Khan, A.; Marson, C. M.; Porter, R. A. Tetrahedron Lett 1995, 36, 33, 5979-5982) to that described for the preparation of 207 was followed using NRB (200 mg, 0.39 mmol) in dimethylformamide (2 mL), chloromethyl pivalate (41) (59 mg, 0.39 mmol) in dimethylformamide (0.5 mL), and potassium carbonate (54 mg, 0.39 mmol). Purification by flash chromatography (hexane/ethyl acetate 1:1) afforded 8 as a colourless solid (118 mg, 0.19 mmol, 48%). mp 95-98° C.; 1H NMR (400 MHz, CDCl3) δ 1.18-1.19 (8.4H, m, tBu), 1.25-1.26 (0.6H, m, tBu), 3.38 (0.2H, dd, J=7.9 and 4.5 Hz, W/H-3), 3.45 (0.5H, dd, J=7.9 and 4.5 Hz, Y/H-3), 3.51-3.59 (0.4H, m, 0.2H U/H-2 and U/H-3, 0.2H V/H-2), 3.63-3.64 (0.2H, m, W/H-4), 3.67-3.76 (0.9H, m, 0.2H V/H-3, 0.2H W/H-2 and 0.5H Y/H-2), 3.88-3.92 (0.3H, m, 0.1H U/H-1 and 0.2H V/H-1), 4.00-4.01 (0.5H, dt, J=4.5 and 1.3 Hz, Y/H-4), 4.20-4.21 (0.1H, m, U/H-4), 4.35-4.36 (0.2H, dt, J=4.5 and 1.3 Hz, V/H-4), 4.49-4.52 (0.7H, m, 0.2H W/H-1 and 0.5H Y/H-1), 5.26-5.29 (0.7H, m, CH2), 5.31-5.62 (3H, m, 1.3H CH2, 0.2H V/H-6, 0.5H Y/H-6 and 1H OH), 6.04-6.06 (0.3H, m, 0.1H U/H-6 and 0.211 W/H-6), 6.71-7.57 (16H, m, Ar), 8.42-8.50 (0.6H, m, 0.2H 2U/αPyr and 0.4H 2VαPyr), 8.54-8.55 (0.7H, m, 0.2H W/αPyr and 0.5H Y/αPyr), 8.61-8.63 (0.7H, m, 0.2H W/αPyr and 0.5H Y/αPyr); vmax(nujol)/cm−1 1140 and 1212 (C—O ester), 1586 (C═O imide), 1715 (C═O ester); m/z (FAB+) 626 (MH+, 67%), 120 (100); (Found: MH+ 626.2644, C39H36N3O5 requires 626.2655).
