To 6-chloro-5-(5,5-dimethyl-1,3,2-dioxaborinan-2-yl)-1H-indole (118 mg, 0.446 mmol) in anhydrous 1,4-dioxane (3.7 mL) and anhydrous DMF (0.74 mL) was added N,N-dimethylformiminium chloride (114 mg, 0.892 mmol). The reaction mixture was stirred for 10 min at room temperature, yielding a thick suspension. The reaction mixture was treated with 2N aqueous potassium carbonate (1.1 mL, 2.2 mmol), 3-(4-bromophenyl)-1-methylpyrrolidine (120 mg, 0.446 mmol), and [1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II) (26 mg, 0.036 mmol). The resulting mixture was heated at 90° C. for 30 min. The reaction mixture was cooled and partitioned between water and EtOAc. The aqueous phase was extracted twice with EtOAc, and the combined organic phases were dried over sodium sulfate and concentrated in vacuo to give 6-chloro-5-[4-(1-methylpyrrolidin-3-yl)phenyl]-1H-indole-3-carbaldehyde (0.23 g, 16% yield) which was used directly in the next step. MS (ES+) 339.0 (M+H)+.
