Synthesis of Ent-16-hydroxycleroda-4(18),13-dien-15,16-olide and Ent-cleroda-4(18),13-dien-15,16-olide from (+)-hardwickiic acid

The absolute configurations of two natural diterpene butenolides were confirmed through the synthesis of ent-16-hydroxycleroda-4(18), 13-dien-15,16-olide (2) and ent-cleroda-4(18), 13-dien-15,16- olide ( 3), enantiomers of the natural products, starting from (+)- hardwickiic acid ( 1).