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. Author manuscript; available in PMC: 2011 Jun 26.
Published in final edited form as: Tetrahedron. 2010 Jun 26;66(26):4784–4795. doi: 10.1016/j.tet.2010.04.006

Scheme 3.

Scheme 3

Synthesis of hexacycle 18 and dehydration product 21. Conditions: a) Tf2O, 2,6-di-tert-butyl-4-methylpyridine, CH2Cl2, −78 °C, 2 h, 78%. b) DIBAL-H, CH2Cl2, −78 °C, 2 h, 100%. c) AcOH, C6D6, 23 °C, 1.8 h, 68%.