Scheme 1. Synthesis of the compounds 14–19a.
aReagents and conditions: (a) K2CO3, DMF, 90°C, 12 h; (b) Hydrazine monohydrate, EtOH, reflux, overnight; (c) Propionaldehyde, THF/MeOH, rt, 30 min, then NaBH4, MeOH, rt, 2 h; (d) NaBH(OAc)3, DCM, rt, overnight.