Scheme 2.

Synthesis of 3-substituted daphnetin derivatives. Reagents and conditions: (a) phenylacetic acid, AcONa, Ac₂O, 6 h, 160 °C, 58%; (b) malononitrile, CH₃COONH₄, H₂O, rt, 3 h; HCl (2 mol/L), 75 °C, 1 h, 80%; (c) ethyl acetoacetate, piperidine, MeOH, reflux, 3 h, 85%; (d) Meldrum′s acid, CH₃COONH₄, H₂O, rt, 4 h, 83%; (e) 2-propynylamine, 1-hydroxybenzotriazole, EDCI, DMF, 5 °C, 5 h, 74%; (f) diethyl malonate, CH₃COONH₄, H₂O, 50 °C, 5 h, 76%; (g) ethyl 2-(benzo[d]thiazol-2-yl) acetate, piperidine, MeOH, 40 °C, 5 h, 88%.