developed
Scheme 1: Synthetic route developed for intermediates 17-19 and Brs analog 20. Conditions and reagents: a. K2CO3/MeOH, r.t. 1.5 h, 85%. b. Pb(OAc)4/Cu(OAc)2/ C6H6, reflux, 2.5 h, 72.3%. c. K2CO3/MeOH, r.t. 6 h, 98%. d. OsO4 4%, (CH3)2CO/NMO, r.t. 12 h, 68%.