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The synthetic strategy for the target compounds. Reagent and conditions: (a) diethyl oxalate, NaH, toluene, 45 oC, 2 h; (b) C2H5OH, reflux, 12 h; (c) (i) Na, C2H5OH, diethyl oxalate, 15 h, (ii) HCl, refluxing, 12 h; (d) LiOH, H2O, THF, rt, 12 h; (e) (i) SOCl2, CH2Cl2, reflux, 2 h, (ii) pyridine, CH2Cl2, 25 oC, 12 h.
