Step 3: 6-Iodobenzodihydropyran (1.0 g, 3.85 mmol), pinacol ester of bisboronic acid (1.22 g, 4.81 mmol) and potassium acetate (1.10 g, 11.5 mmol) were dissolved in DMF (36 mL), and the solution was degassed by argon for 5 min. Subsequently, PdCl2(dppf)-DCM complex (314 mg, 0.38 mmol) was added and the reaction mixture was again degassed for 5 min. The reaction system was heated to 95 °C with continuous stirring for 5 hours. After completion of the reaction, it was cooled to room temperature. The crude reaction mixture was diluted with water and extracted three times with ethyl acetate (3 x 100 mL). The organic phases were combined and washed sequentially with water (100 mL) and brine (100 mL). The organic layer was dried over anhydrous magnesium sulfate, filtered and concentrated. The crude product was further purified by the CombiFlash system using gradient elution with ethyl acetate/hexane to afford the target product 3,4-dihydrochromene-6-boronic acid ester (840 mg, 84% yield).
