A protecting-group-free synthesis of (+)-nephrosteranic, (+)-protolichesterinic, (+)-nephrosterinic, (+)-phaseolinic, (+)-rocellaric acids and (+)-methylenolactocin

A collective synthesis of a gamma-butyrolactone class of paraconic acids such as (+)-methylenolactocin, (+)-phaseolinic acid, (+)-nephrosteranic acid, (+)-nephrosterinic acid, (+)-rocellaric acid and (+)-protolichesterinic acid is described. The strategy adopted is protecting-group-free based on efficient Pd-catalyzed Suzuki-Miyaura coupling and Ru-catalyzed Sharpless oxidation to construct the core beta-CO2H-gamma-butyrolactone unit to accomplish the synthesis of various paraconic acids.