Scheme 5.

Synthesis of 11, 12 and 13^a

^aReagents and conditions: (a) BH₃-SMe₂, THF, −78-25°C, 12.5h. (b) pyridine sulfur trioxide, Et₃N, DMSO, 25°C, 12h. (c) i. THF, t-BuOK, N₂, −20°C, 2h, ii. Pd/C, H₂, MeOH, 25°C, 2h. (c’) i. Pd(dppf)Cl₂, dioxane, H₂O, K₂CO₃, N₂, 25-100°C, 2h. ii. Pd/C, H₂, MeOH, 25°C, 2h. (d) LiOH•H₂O, MeOH, THF, H₂O, 25-70°C, 2h. (e) HATU, Et₃N, THF, 25°C, 12h.