Step 2. Synthesis of 6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoline
A tetrahydrofuran (20 mL) solution of 6-bromoquinoline (5 g, 23.92 mmol, 1.00 equiv) was added to a pre-dried and purged 100 mL round bottom flask under nitrogen protection. Potassium acetate (KOAc, 3.55 g, 1.50 eq.), pinacol ester of bisboronic acid (18.23 g, 71.77 mmol, 3.00 eq.), and [1,1'-bis(diphenylphosphino)ferrocene]palladium(II) dichloride (Pd(dppf)2Cl2, 1.95 g) were then added sequentially. The reaction mixture was placed in an oil bath at 80 °C and the reaction was stirred overnight. After completion of the reaction, the insoluble solids were removed by filtration. The filtrate was concentrated under reduced pressure and purified by silica gel column chromatography with the eluent ethyl acetate/petroleum ether (1:50, v/v). 6.62 g (109% yield) of 6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quinoline was finally obtained as a red oil.
