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. Author manuscript; available in PMC: 2017 Apr 27.
Published in final edited form as: J Am Chem Soc. 2016 Apr 12;138(16):5426–5432. doi: 10.1021/jacs.6b02276

Scheme 3. Synthesis of the Acyclic Advanced Precursors 29a–ca.

Scheme 3

aReagents and conditions: (a) carbonyldiimidazole (CDI), 4 Å molecular sieves, DMF, then malonic acid half-thioester, magnesium ethoxide (Mg(OEt)2), 23 °C, 95%; (b) 17, 23, or 27, AgO(TFA), Et3N, DMF, 0 °C, 90% (29a), 87% (29b), 86% (29c).