[CH3:1][C:2]1([CH3:14])[C:6]([CH3:8])([CH3:7])[O:5][B:4]([C:9]2[CH:10]=[N:11][NH:12][CH:13]=2)[O:3]1.C(=O)([O-])[O-].[Cs+].[Cs+].[Cl:21][CH2:22][CH2:23]Br>CS(C)=O.CCOC(C)=O>[Cl:21][CH2:22][CH2:23][N:12]1[CH:13]=[C:9]([B:4]2[O:5][C:6]([CH3:7])([CH3:8])[C:2]([CH3:14])([CH3:1])[O:3]2)[CH:10]=[N:11]1To a solution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole (1.0 G, 5.2 mmol) in 30 mL of DMSO was added cesium carbonate (6.73 G, 20.6 mmol) and 2-chloroethylbromide (0.854 mL, 10.3 mmol). This reaction mixture was stirred at room temperature for 4 hours. The reaction mixture was then diluted with a large volume of EtOAc. The organic was washed with water ×1, saline ×1, then dried over Na2SO4 and conc. to give 1-(2-chloroethyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole as a solid.
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