Studies toward the synthesis of spirolides: assembly of the elaborated E-ring fragment

A stereoselective synthesis of the spiroimine fragment of spirolide C is described. The congested C7 and C29 tertiary and quaternary centers are constructed by a diastereoselective Ireland-Claisen rearrangement. The E ring is completed by means of an aldol cyclocondensation. Additional studies were preformed on the advanced intermediate to probe a future coupling strategy.