Scheme 3. Synthesis of Compound 4–5a.

aReagents and conditions: (a) NaOAc, HOAc, 120 °C; (b) Pd(PPh3)2Cl2, CuI, TEA, DMF, 80 °C; (c) TFA, DCM, rt; (d) HATU, DIPEA, DMF, rt.

aReagents and conditions: (a) NaOAc, HOAc, 120 °C; (b) Pd(PPh3)2Cl2, CuI, TEA, DMF, 80 °C; (c) TFA, DCM, rt; (d) HATU, DIPEA, DMF, rt.