Scheme 1.

Syntheses of Intermediates VIa–r and Analogues 1–9^a

^aReagents and conditions: (a) SOCl₂, CH₂Cl₂, 4 h, and 91–100%; (b) MgBr₂·OEt₂, iPr₂NEt, CH₂Cl₂, 12 h, and 60–69%; (c) Cs₂CO₃, DMSO, 1 h, and 55–83%; (d) (i) pyrrolidine (0.5 equiv), TsOH (0.5 equiv), EtOH, reflux, and 1–2 h and (ii) ethyl 2-hydrazinylthiazole-4-carboxylate·HBr and reflux overnight; and (e) LiOH, THF/MeOH/H₂O, and 1 h.