[CH3:1][C:2]1([CH3:21])[C:10]2[C:5](=[CH:6][C:7]([B:11]3[O:15][C:14]([CH3:17])([CH3:16])[C:13]([CH3:19])([CH3:18])[O:12]3)=[CH:8][CH:9]=2)[NH:4][C:3]1=[O:20].I[CH:23]1[CH2:26][O:25][CH2:24]1.C1COCC1.C[Si]([N-][Si](C)(C)C)(C)C.[Na+]>CN(C=O)C.CCOC(C)=O.O.[Cl-].[Na+].O>[CH3:1][C:2]1([CH3:21])[C:10]2[C:5](=[CH:6][C:7]([B:11]3[O:15][C:14]([CH3:17])([CH3:16])[C:13]([CH3:19])([CH3:18])[O:12]3)=[CH:8][CH:9]=2)[N:4]([CH:23]2[CH2:26][O:25][CH2:24]2)[C:3]1=[O:20]To a solution of 3,3-dimethyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)indolin-2-one (56 mg, 0.20 mmol) and 3-iodooxetane (85 μL, 0.98 mmol) in DMF (1 mL) was added a THF solution of NaHMDS (1.0 M, 0.21 mL, 0.21 mmol). After 1.5 h, the reaction mixture was heated to 70° C. After an additional 1.5 h, the reaction mixture was cooled to r.t. and additional 3-iodooxetane (30 μL, 0.34 mmol) and NaHMDS solution (0.1 mL, 0.1 mmol) were added. The reaction mixture was heated to 70° C. and was stirred an additional 16 h. The reaction mixture was cooled and diluted with EtOAc, water, and brine, and the layers were separated. The organic phase was washed with brine, dried over Na2SO4, filtered, and concentrated. The crude residue was purified by silica gel chromatography (0-50% EtOAc in hexanes) to provide 3,3-dimethyl-1-(oxetan-3-yl)-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)indolin-2-one (7.43). LCMS-ESI+ (m/z): [M+H]+ calcd for C19H27BNO4: 344.20; found: 316.25.
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