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Scheme 1. The synthesis of the target compounds G1–G8. Reactions and conditions: (a) HCl/H2O, r.t., 5 h, in 91% yield; (b) Ac2O, DCM, Et3N, r.t., 20 h, in 88% yield; (c) CDI, Et3N, toluene, reflux, 48 h, in 93% yield; (d) 1f–8f, DBU, DMF, r.t., 24 h, in 17–25% yield; (e) Pd/C, H2, MeOH, r.t., in 70–80% yield; (f) CH3OH, 55 °C, 20 h, 62–75% yield.
