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Synthetic route of compound 3 derivatives. Reagents and conditions: (a) concentrated H2SO4, EtOH, 80 °C, 2 h, 65%; (b) POCl3, DMF, rt-50 °C, 4 h, 87%; (c) Al(O-i-Pr)3, i-PrOH, 60 °C, 5 h, 85%; (d) p-(trifluoromethyl)benzyl alcohol or o-fluorobenzyl alcohol, K2CO3, DMF, rt, 3–5 h, 89–93%; (e) Pd(OAc)2, Cs2CO3, Xphos, 1,4-dioxane, 100 °C, 2–4 h, 68–85%; (f) NaOH, MeOH/H2O (3:1 v/v), 80 °C, 1.5 h, 45–52%.
