Scheme 1. Synthesis of anhydride 5. Reagents and conditions; (a) TBSCl (1.2 eq.), imidazole (1.5 eq.), DMAP (0.05 eq.), DCM : DMF (6 : 1), r.t., 22 h, 79%; (b) (E)-2-(but-1-en-1-yl)benzo[d][1,3,2]dioxaborole 22 (1.2 eq.), Pd(PPh3)2Cl2 (0.05 eq.), KOAc (2 eq.), PhMe, H2O, reflux, 16 h 79%; (c) 1-(tert-butyldimethylsilyloxy)-1-tert-butoxyethylene (2.04 eq.), Pd(PTol3)2Cl2 (0.05 eq.), KOAc (2 eq.), THF, reflux, 16 h, 93%; (d) HF–Py (70 : 30) (3 eq.), THF, 0 °C to r.t., 18 h, 46%; (e) DMP (3 eq.), DCM, 0 °C to r.t., 16 h, 86%; (f) TFA (excess), 66%.
