Scheme 3. Demethylation of diarylbenzofuran 5. Reagents and conditions: (a) BBr₃, DCM, N₂,−45 °C -r.t, overnight, 36%; (b) Br₂, DCM, 0 °C, 6 h, 80%; (c) BBr₃, DCM, N₂, −45 °C -r.t, overnight, 39%; (d) 10% Pd–C, H₂ (0.6 MPa), 16 h, 79%; (e) BCl₃, TBAI, Ar, 0 °C, 6 h, 65%.