Scheme 3.
Synthesis of 23–25. Reagents and conditions: (a) NH2NH2•H2O, EtOH; (b) NaOH, EtOH, H2O, reflux; (c) NaNO2, H2O, HCl 6N, 0 °C; (d) MeOH, CH3COONa, 0 °C.
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