Total Synthesis of Gymnocin-A.

A convergent total synthesis of cytotoxic marine natural polycyclic ether, gymnocin-A (1), is described. The synthesis features three iterations of an oxiranyl anion strategy, involving base-mediated cycloetherification, ring expansion, and reductive etherification, for the construction of the FGH fragment and for its coupling with the ABC and KLMN fragments.