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. Author manuscript; available in PMC: 2020 Dec 1.
Published in final edited form as: Bioorg Med Chem Lett. 2019 Oct 14;29(23):126713. doi: 10.1016/j.bmcl.2019.126713

Scheme 1.

Scheme 1.

Synthesis of advanced intermediates I to V. Reagents and conditions: (i) 2 M sodium carbonate in water, palladium(0)tetrakis(triphenylphosphine), dimethoxyethane, 90 °C; (ii) formic acid, 21–25 °C; (iii) 12 M aq. HCl, dioxane, reflux; (iv) 4 M aq. HCl, dioxane, 50 °C.