Reaction Steps
Benzyl chloroformate (1.07 g) was added dropwise to a stirred ice cold mixture of the (1S,9S)t-butyl 9-amino-6,10-dioxo-1,2,3,4,7,8,9,10-octahydro-6H-pyridazino[1,2-a][1,2]diazepine-1-carboxylate (GB 2,128,984; 1.55 g, 5.21 mmol), NaHCO3 (0.66 g, 7.82 mmol), dioxan (32 ml) and water (8 ml). The mixture was kept at 5° C. for 15 min then for 2 h at room temperature. The mixture was diluted with EtOAc (50 ml), washed twice with sat. NaHCO3 solution, dried (MgSO4) and concentrated. The oily residue was purified by flash chromatography to afford 211d (1.98 g, 88%) of a colourless oil: [α]D24 −56.4 (c 1.0, CH2Cl2); IR(thin film) 3325, 2979, 2946, 1728, 1677, 1528, 1456, 1422, 1370, 1340, 1272, 1245, 1156, 1122, 1056, 916, 734, 699; 1H NMR (CDCl3) δ 7.29 (5H, m), 5.81-5.72 (1H, m), 5.26-5.20 (1H, m), 5.05 (2H, s), 4.69-4.51 (2H, m), 3.48-3.36 (1H, m), 2.81-2.51 (2H, m), 2.34-2.19 (2H, m), 1.90-1.54 (4H, m), 1.41 (9H, s); Anal. Calcd for C22H29N3O6.H2O: C, 58.79; H, 6.92; N, 9.35. Found: C, 59.10; H, 6.57; N, 9.25; MS (ES+) 454 (M++Na, 87%), 432 (M++1, 100).
