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Reagents and conditions: (a) SEMCl or MEMCl, DIEA or NaH, THF. (b) Ethyl pyrazole-4-carboxylate, Cs2CO3, DMF, 80 °C, 1−5 h. (c) 4 M HCl/dioxane, EtOH, reflux, 1 h. (d) LiOH, THF/H2O. For R1−3 groups, see Table 2.
