Total Synthesis of Belizentrin Methyl Ester: Report on a Likely Conquest

The assigned structure of the dinoflagellate-derived toxin belizentrin was prepared by total synthesis in form of the corresponding methyl ester for stability reasons. The successful route features an unusual solution for the preparation of a recalcitrant ylide on a C-glycosidic segment; moreover, it involves an asymmetric hetero-Diels-Alder reaction en route to the tertiary hemiacetal substructure, a Negishi cross-coupling of two elaborate building blocks, and a macrocyclization based on an intramolecular aminolysis of a spirolactone. A modified Kocienski olefination ultimately allowed the polyol side chain to be attached to the macrocycle although this transformation faced the exceptional base sensitivity of this polyunsaturated target compound.