Total synthesis of (-)-spirotryprostatin B: synthesis and related studies

The total synthesis of spirotryprostatin B, a cytostatic spiropyrrolidine-3,3'-oxindole] alkaloid, is described. The key step of the synthetic approach consists of the application of the MgI2-mediated ring-expansion reaction of a spirocyclopropane-1,3'-oxindole] with an aldimine, leading to rapid assembly of the spirotryprostatin core. The route documents the installation of the prenyl side chain by Julia-Kocieński olefination of a key aldehyde precursor, a transformation that ultimately allows for facile synthesis of analogues and facilitates structure-activity relationships studies.