Total synthesis of everninomicin 13,384-1--Part 2: synthesis of the FGHA2 fragment.

The stereoselective synthesis of everninomicin's 13,384-1 (1) FGHA2 fragment (2) in a suitable form for incorporation into the final target (1) is described. The construction of the FG 1,1'-disaccharide linkage relied on a new method based on tin-acetal chemistry, while for the GH orthoester bridge, a number of approaches were explored. Final success for the latter construction came when a novel 1,2-phenylseleno migration reaction was applied to couple rings G and H, followed by ketene acetal and orthoester formation.