Scheme 4.

Synthesis of compound 8r^a

^aReagents and conditions (a) DPPA, Et₃N, t-BuOH/toluene/1,2-dichloroethane 1.5:1.5:1, RT to reflux, 32%. (b) HCl/dioxane, then NaHCO₃, RT, 99%. (c) NaNO₂/aq. HCl, then CuSO₄, SO₂, AcOH/water, −10 °C to RT, 36%. (d) PhNH₂, Et₃N, THF, RT, 84%. (e) PhSH, Cs₂CO₃, CH₃CN, RT, 79%. (f) EDCI, HOBt, 3-methylfuran-2-carboxylic acid, DMF, RT, 76%.