Scheme 1:

Synthesis of compounds (±)-6a-f^a

^aReagents and conditions: a) Appropriate aryl aldehyde, Cs₂CO₃, 1,4- dioxane, 110 °C, 14 h, 40–100%; b) phenylhydrazine, H₂SO₄, 1,4-dioxane, 70 °C, 2 h then 25 °C, 14 h, 30–66%; c) NaBH₄, MeOH, 25 °C, 12 h or H₂/Pd, MeOH, 25 °C, 12 h, 40–100%; d) methyl 4-formylbenzoate, NaBH₃CN, EtOH, AcOH, 70 °C, 14 h, 25–43%; e) NH₂OH (50% in H₂O), KOH, DCM/MeOH from 0 °C to 25 °C, 12 h, 33–73%.