[Si:1]([O:8][CH2:9][CH:10]([OH:23])[CH2:11][N:12]1[CH:16]=[C:15]([N+:17]([O-:19])=[O:18])[N:14]=[C:13]1[N+]([O-])=O)([C:4]([CH3:7])([CH3:6])[CH3:5])([CH3:3])[CH3:2].[H-].[Na+]>CN(C=O)C>[Si:1]([O:8][CH2:9][CH:10]1[O:23][C:13]2=[N:14][C:15]([N+:17]([O-:19])=[O:18])=[CH:16][N:12]2[CH2:11]1)([C:4]([CH3:7])([CH3:6])[CH3:5])([CH3:3])[CH3:2]A solution of alcohol 88 (2.04 g, 5.89 mmol) in anhydrous DMF (20 mL) under N2 at −20° C. was treated with 60% NaH (0.34 g, 8.50 mmol). After stirring at −20 to −10° C. for 50 min, the reaction was quenched with EtOAc and water (150 mL), and extracted with EtOAc (500 mL). The extract was washed with water (2×100 mL) and brine (100 mL), backextracting with EtOAc (100 mL), and then the solvent was removed. Chromatography of the residue on silica gel, eluting with 40-67% EtOAc/petroleum ether, gave 2-({[tert-butyl(dimethyl)silyl]oxy}methyl)-6-nitro-2,3-dihydroimidazo[2,1-b][1,3]oxazole (89) (1.13 g, 64%) as a pale yellow solid: mp (EtOAc/petroleum ether) 142-144° C.; 1H NMR (CDCl3) δ 7.52 (s, 1H), 5.33 (m, 1H), 4.29 (d, J=7.2 Hz, 2H), 4.05 (dd, J=11.9, 3.5 Hz, 1H), 3.86 (dd, J=11.9, 2.8 Hz, 1H), 0.81 (s, 9H), 0.08, 0.03 (2 s, 2×3H). Anal. (C12H21N3O4Si) C, H, N.
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