Compound 5 (0.2 g, 0.32 mmol) and compound 6 (0.09 g, 0.38 mmol) were added into a 50 mL single-necked round-bottomed flask, and EtOH (10 mL) was added. Then, 200 μL of hexahydropyridine were transferred to the reaction solution with a pipette, and the reaction system was heated and refluxed at 85 ℃ overnight. The reaction system was cooled to room temperature, then distilled under reduced pressure and spin-dried. The crude product was purified by flash chromatography on SiO2 (DCM / MeOH = 20:1, v/v) to obtain a purple needle crystal (0.15 g, yield 55 %).