Synthesis of (+)-Hypoxylactone through Allenoate γ-Addition: Revision of Stereochemistry

A synthesis of (+)-hypoxylactone has been accomplished in four steps starting from the allenoate γ-addition of threo-3-chloro-2-silyoxybutanals, leading to the revision of stereochemistry. The key was the discovery of control elements required to matching/mismatching cases in the allenoate γ-addition to provide the desired adducts as a single isomer. The utility of the γ-adduct was demonstrated with the Au(I)-catalyzed cyclization to afford (+)-xylogiblactone A. Use of Ag₂O was the key to epoxidation for preventing epimerization of the γ-lactone ring.