Scheme 1. Reagents and conditions: (a) CH₃COONa, CH₃COOH, ethyl levulinate, 70 °C, 5–10 min; (b) H₂SO₄, C₂H₅OH, reflux 3–4 h; (c) 6 N NaOH, EtOH, room temperature, 3 h; (d) DMF, EDC·HCl, DMAP, 0 °C, 20–30 min; (e) morpholine, room temperature, overnight; (f) Ar₂, LiAlH₄, THF, 0 °C to room temperature, 2 days; (g) Ar₂, HMPA, KHMDS, THF, –78 °C; (h) Ar₂, –22 °C, 30 min; (i) Ar₂, room temperature, 2–3 h.