Scheme 4:

Synthesis of compound (±)-6m^a

^aReagents and conditions: a) 3-Pyridinecarboxaldehyde, Cs₂CO₃, dioxane, 110 °C, 14 h, 100%; b) phenylhydrazine, H₂SO₄, dioxane, 70 °C, 2 h, 14%; c) Boc₂O, THF, NaOH, 25 °C, 2 h, 100%; d) H₂ Pd/C, MeOH, 25 °C, 12 h, 100%; e) methyl 4-formylbenzoate, NaBH₃CN EtOH, AcOH, 70 °C, 14 h, 30%; f) NH₂OH (50% in H₂O), KOH, DCM/MeOH from 0 °C to 25 °C, 12 h, 51%.