Scheme 2. Derivatization of chromene diones by selective O-demethylation, O-acetylation and O-triflation starting from 11a,b,d (A), 11c (B), 16b (C), respectively. Reagents and conditions: (a) BBr₃ (1.1–2.5 eq.), DCM, −78 °C (11d) or 0 °C (11a,b) to rt, 20 h. (b) Ac₂O (135–200 eq.), pyridine (160–235 eq.), DCM, rt, 21 h. (c) BBr₃ (5.0 eq.), DCM, 0 to 40 °C, 3 d. (d) Ac₂O (1.05–1.1 eq.), pyridine (1.05–1.5 eq.), DCM, rt, 17–20 h. (e) Tf₂O (2.2 eq.), pyridine (2.2 eq.), DCM, 0 °C to rt, 4.5 h. (f) Tf₂O (1.05–1.1 eq.), pyridine (1.05–1.5 eq.), DCM, 0 °C to rt, 4.5 h. (g) BBr₃ (3.5 eq.), DCM, −78 °C to rt, 7 d.