Scheme 3.

Synthesis of Pyridyl Series Compounds 25–33^a

^aR³ and R⁴ are defined in Table 3. Synthesis of 58 was reported in Scheme S1. Conditions: (a) R³-boronic acid, PdCl₂(dppf)·CH₂Cl₂, K₂CO₃, 1,4-dioxane/H₂O, 90 °C, overnight, 90%; (b) TFA, anisole, CH₂Cl₂, rt, overnight, 87%; (c) LiBHEt₃ (1 M THF), THF, 0 °C, 1 h, quant.; (d) PBr₃, CH₂Cl₂, 0 °C, quant.; (e) 2-methyl-1H-imidazole, MeCN, 50 °C, overnight, 70%; (f) R⁴-pyridylmethyl halide, NaH, DMF, 0 °C, 2 h, 25–71%.