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The mixture of compound 2 (5 g, 0.024 mol) and compound 3 (3.7 g, 0.024 mol) was heated to 160-180 C. under N2 for 2 h. After cooled to RT, the reaction mixture was dissolved in MeOH (5 mL) at 70 C. Then the mixture was cooled to RT, the formed precipitate was filtered and washed with MeOH, dried to give compound 4 (3.0 g, 40% yield) as yellow solid.