Cl.[OH:2][CH:3]1[CH2:7][NH:6][C@H:5]([C:8]([O:10][CH2:11][CH3:12])=[O:9])[CH2:4]1.[C:13]([O:17][C:18](N=[N+]=[N-])=[O:19])([CH3:16])([CH3:15])[CH3:14].C(N(CC)CC)C.O>O1CCOCC1>[C:13]([O:17][C:18]([N:6]1[CH2:7][CH:3]([OH:2])[CH2:4][C@H:5]1[C:8]([O:10][CH2:11][CH3:12])=[O:9])=[O:19])([CH3:16])([CH3:15])[CH3:14]A stirred mixture of 100 g (510 mmol) of 5, 75.0 mL (540 mmol) of t-butoxycarbonylazide, 150 mL of triethylamine, 500 mL of water and 500 mL of p-dioxane was heated under nitrogen to 50° C. for 15 h. The mixture was reduced in volume by one half on a rotary evaporator and extracted with four 100 mL portions of ether. The combined extracts were washed with brine, dried over magnesium sulfate and concentrated to a yellow oil under reduced pressure. Distillation of the oil under reduced pressure gave 97.5 g (69.6%) of 6 was a pale yellow oil: bp 126°-128° C. (0.05 mm); 1H NMR (CDCl3) δ1.27 (t, 3H, J=7 Hz), 1.45 (s, 9H), 1.8-2.4 (m), 3.4-3.7 (m), 4.2 (q, 2H, J=7 Hz), 4.4-4.6 (m); 13CNMR (CDCl3) δ14.2, 28.2, 28.3, 38.2, 39.0, 54.4, 57.7, 58.0, 60.9, 68.7, 69.4, 79.9, 80.1, 153.8, 154.3, 172.7, 173.0; IR (neat) 3450, 1735, 1680 cm-1. [α]D20 -68.3° C. (c=2, EtOH) (lit. [α]D20 -67.8° C. (c=1.75, EtOH).
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