[Si:1]([O:8][CH2:9][C:10]1[CH:19]=[CH:18][C:13]([C:14]([NH:16][NH2:17])=[O:15])=[CH:12][CH:11]=1)([C:4]([CH3:7])([CH3:6])[CH3:5])([CH3:3])[CH3:2].Cl.[C:21](=N)(OCC)[CH2:22][CH3:23].CCN(CC)CC>CCO>[Si:1]([O:8][CH2:9][C:10]1[CH:11]=[CH:12][C:13]([C:14]2[O:15][C:21]([CH2:22][CH3:23])=[N:17][N:16]=2)=[CH:18][CH:19]=1)([C:4]([CH3:7])([CH3:6])[CH3:5])([CH3:3])[CH3:2]To a solution of 4-(((tert-butyldimethylsilyl)oxy)methyl)benzohydrazide (6.0 g, 21.4 mmol; reported in Tanaka, A. et al. J. Med. Chem. 1998, 41, 2390) and ethyl propionimidate hydrochloride (3.5 g, 25.7 mmol; preparation reported in WO2007/73299 A1) in EtOH (120 mL) was added Et3N (2.59 g, 25.7 mmol). The mixture was stirred at room temperature for 1 hr then concentrated in vacuo. The residue was partitioned into EtOAc and H2O and the organics were washed with H2O and brine, dried over Na2SO4 and concentrated in vacuo. Purification by chromatography (EtOAc-hexanes) gave 2-(4-(((tert-butyldimethylsilyl)oxy)methyl)phenyl)-5-ethyl-1,3,4-oxadiazole as a brown oil (3.0 g, 44% yield).
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