N1C=CN=C1.[CH3:6][C:7]([Si:10](Cl)([CH3:12])[CH3:11])([CH3:9])[CH3:8].[CH2:14]([C:16]1[O:17][C:18]([CH2:21][CH2:22][OH:23])=[CH:19][CH:20]=1)[CH3:15]>CN(C=O)C.C(OCC)C>[C:7]([Si:10]([O:23][CH2:22][CH2:21][C:18]1[O:17][C:16]([CH2:14][CH3:15])=[CH:20][CH:19]=1)([CH3:12])[CH3:11])([CH3:9])([CH3:8])[CH3:6]Imidazole (255 mg, 3.75 mmol) and TBSCl (414 mg, 2.75 mmol) were added to the solution of 245A (350 mg, 2.5 mmol) in DMF (4 mL). The mixture was stirred at rt for 15 hr and then 100 mg (0.66 mmol) of additional TBSCl was added to drive the reaction to completion. After stirring for an additional hour, the reaction mixture was diluted with diethylether (100 mL) and washed with water (20 mL), 1 N HCl (20 mL), water (20 mL) and brine (20 mL). The organic layer was dried over Na2SO4 and concentrated under reduced pressure to give 509 mg of compound 434A (80.3%) as a yellow oil.
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