A mixture of 1-tert-butyl 5-methyl 3-iodo-1H-indole-1,5-dicarboxylate (6 g, 14.96 mmol) and tert-butyl 1-(6-(tributylstannyl)pyrazin-2-yl)piperidin-4-ylcarbamate (1d) (10.2 g, 17.95 mmol) in DMF (60 mL) was purged with argon gas for 5 min, added CuI (4.27 g, 22.44 mmol), palladium tetrakis (1.7 g, 1.5 mmol) and again purged with argon gas for 5 min. The reaction mixture was stirred at 90° C. under nitrogen atmosphere for 1 h. The reaction mixture was then poured into water. The resulting precipitate was collected by filtration. The filtrate was extracted with diethyl ether. The organic layer was concentrated and combined with the above precipitate to give the crude product. Purification was carried out by column chromatography to obtain the title compound as a brown solid (2.5 g, 30%). MS (ESI, pos. ion) m/z: 552.2 (M+1).
