To cesium carbonate (641 mg, 1.968 mmol, 2 equiv) was added 3-ethoxyphenol (272 mg, 1.968 mmol, 2 equiv) in 4 mL of NMP. The reaction mixture was degassed and filled with nitrogen 3 times (3 cycles vacuum/nitrogen). 4-(4-bromophenyl)-5-methyl-2,4-dihydro-3H-1,2,4-triazol-3-one (Intermediate 22, 250 mg, 0.984 mg, 1 equiv), 2,2,6,6-tetramethyl-3,5-heptanedione (18 mg, 0.098 mmol, 0.1 equiv) and copper chloride (58 mg, 0.590 mmol, 0.6 equiv) were added. The reaction mixture was degassed and filled with nitrogen 3 times (3 cycles vacuum/nitrogen) and then warmed to 120 C under nitrogen overnight. The reaction mixture was diluted with dichloromethane and filtered. Volatiles were removed in vacuo and the residue was purified by preparative HPLC to give the title compound (20.2 mg).
