Synthesis of the spiroacetal core of the cephalosporolide family of natural products

The synthesis of four possible stereoisomers of the spiroacetal core of the natural products cephalosporolides H and I and penisporolides A and B is described. The key steps involve the use of Sharpless asymmetric dihydroxylation to install the desired stereochemistry of the γ-lactone ring and an oxidative radical cyclisation to form the spiroacetal ring system.