Scheme 4.

Fragment Coupling and Completion of the Synthesis^a

^aReagents and conditions: (a) NaOH, MeOH, rt, 83%; (b) NaIO₄, THF/H₂O, rt, 30 min, 96%; (c) (CH₃)₃SI, n-BuLi, THF, −13 to 5 °C, 73%; (d) TESCl, imidazole, DMF, rt, 95%; (e) (SO₂CF₃)₂NC₅H₃NCl, LHMDS, THF, −78 °C, quant.; (f) 9-BBN dimer, THF, 60 °C, 20 h; (g) PdCl₂(dppf), aq. Cs₂CO₃, THF/DMF/H₂O, 40 °C, 36 h, 78% (h) TBAF, THF, rt, 83%.