Total synthesis of everninomicin 13,384-1 - Part 2: Synthesis of the FGHA(2) fragment

The stereoselective synthesis of everninomicin's 13,384-1 (1) FGHA(2) fragm ent (2) in a suitable form for incorporation into the final target (1) is d escribed. The construction of the FG 1,1'-disaccharide linkage relied on a new method based on tin-acetal chemistry, while for the GH orthoester bridg e, a number of approaches were explored. Final success for the latter const ruction came when a novel 1,2-phenylseleno migration reaction was applied t o couple rings G and H, followed by ketene acetal and orthoester formation.