Scheme 1.
a Reagents and conditions: (i) K2CO3, EtOH, 60 °C, 5 h; (ii) POCl3, dioxane, reflux, 2 h; (iii) NaOEt, EtOH, 50 °C 3 h; (iv) LiOH, dioxane/H2O; (v) PyBop, DIPEA, DMF followed by addition of amine.
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