Total synthesis of proposed cephalosporolides H and I

An efficient total synthesis toward spiroketal diastereomers of cephalosporolides H and I was achieved, respectively, taking advantage of intramolecular Wacker-type spiroketalization on the common olefin-containing dihydroxy-γ-lactone substrate. By comparing the physical data of natural products with synthetic samples, we suggest that the reported stereochemical assignments for cephalosporolides H and I are incorrect. Our work suggests that the stereochemistry on C-6 of the core spiroketal skeleton should be revised to S from its original R assignment, and the real structures of these natural compounds should be reconsidered.