Synthetic Studies of Halichondrin B, an Antitumor Polyether Macrolide Isolated from a Marine Sponge. 7. Synthesis of Two C27-C36 Units via Construction of the F Ring and Completely Stereoselective C-Glycosylation Using Mixed Lewis Acids

Abstract

Two C27-C36 units of halichondrin B were synthesized starting from a C31-C34 alcohol, which was easily available from dimethyl L-tartrate, via construction of the F ring, methylation at the C31 position and C-glycosylation. These crucial reactions proceeded completely stereoselectively, and in particular the stereoselective C-glycosylation with allyltrimethylsilane took place only in the presence of both of two Lewis acids, boron trifluoride etherate and trimethylsilyl triflate.