[O:1]=[C:2]1[NH:20][C@@H:5]2[CH2:6][N:7]([C:10]([O:12][CH2:13][C:14]3[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=3)=[O:11])[CH2:8][CH2:9][C@@H:4]2[O:3]1.[O:21](C(OC(C)(C)C)=O)[C:22]([O:24][C:25]([CH3:28])([CH3:27])[CH3:26])=O.C(N(CC)CC)C>ClCCl.CN(C1C=CN=CC=1)C>[O:1]=[C:2]1[N:20]([C:22]([O:24][C:25]([CH3:28])([CH3:27])[CH3:26])=[O:21])[C@@H:5]2[CH2:6][N:7]([C:10]([O:12][CH2:13][C:14]3[CH:15]=[CH:16][CH:17]=[CH:18][CH:19]=3)=[O:11])[CH2:8][CH2:9][C@@H:4]2[O:3]1To a solution of (3aR,7aS)-benzyl 2-oxohexahydrooxazolo[4,5-c]pyridine-5(6H)-carboxylate (1.0 equiv.) in dichloromethane (0.09 M) was added BOC2O (1.1 equiv.), triethylamine (1.1 equiv.), and a catalytic amount of DMAP. The reaction was stirred at room temperature for one hour at which point it was concentrated under vacuo and filtered through a plug of silica gel eluting with ethylacetate. The product was dried under vacuo to yield (3aR,7aS)-5-benzyl 3-tert-butyl 2-oxotetrahydrooxazolo[4,5-c]pyridine-3,5(2H,6H)-dicarboxylate as a white solid in 75% yield. LCMS (m/z): 277.2 (MH+), Rt=3.43 min.
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