Scheme 2.
Reagents and conditions for Series-II and -III: (a) EtOH, Conc. H2SO4, reflux, 1.5 h, 92%; (b) Hydrazine hydrate, absolute EtOH, reflux, 6 h, 44%; (c) Ar-CHO, EtOH, glacial acetic acid, reflux, 1.5–3 h, 30–45%.
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