Scheme 1. Synthetic route to chromene dione derivatives. (A) Synthetic pathway to access derivatives 11a–d. (B) Synthesis towards chromene diones 16a,b. Reagents and conditions: (a) 1. n-BuLi (1.5 eq.), DIPA (1.5 eq.), THF, −78 °C, 1 h; 2. 7 (1.0 eq.), −78 °C, 1 h; 3. 6a–c/12a,b (1.1 eq.), −78 °C, 3.5 h. (b) Pd2(dba)3 (2.5 mol%), t-BuBrettPhos (6.0 mol%), TDA (5.0 mol%), NaNO2 (2.0 eq.), t-BuOH, 100 °C, 22 h. (c) Imidazole (1.05 eq.), TBSCl (1.05 eq.), DMF, 0 °C to rt, 16 h. (d) DMP (1.1 eq), DCM, rt, 3–5 h. (e) BBr3 (1.1 eq.), DCM, −78 °C to rt, 13–20 h. (f) FeCl3·6H2O (0.5 eq.), DCM, 40 °C, 24–72 h.
