Scheme 20. Synthetic route of 7-benzyloxy-2,3-dimethyl-4-oxo-4H-chromene-8-carboxamides (39 and 40). Reagents and conditions: (a) (i) AcOH, HMTA, 90 °C, 10 h; (ii) PhCH₂Br, K₂CO₃, 0–80 °C, 5 h; (iii) Jones reagent, 0 °C, 4 h; (iv) R-NH₂, HBTU–HOBT, rt, 20 h.