Strategies for the Total Synthesis of Diverse Bromo-Chamigrenes

Several dozen spirocyclic sesquiterpenoids known as the bromo-chamigrenes have been isolated to date. Yet, despite their unique structures, synthetic efforts toward this collection have been modest. Herein, we outline two strategies to generate their skeletons based on (1) a biomimetic bromonium-induced polyene cyclization using BDSB (Et2SBr·SbCl5Br) and (2) a Diels–Alder reaction which ultimately delivered four members of the class. In addition, X-ray crystallography reveals that one member has a structure in need of revision.