Synthesis of the Halichondrin C1-C15 Fragment from a Halaven C27-C35 Byproduct: Stereospecific Intramolecular Kishi Reduction.

A byproduct from a Halaven C27-C35 manufacturing process was transformed into a crystalline halichondrin C1-C15 building block by employing a stereospecific intramolecular Kishi reduction as the key step.