Total Synthesis and Absolute Configuration of Liverwort Diterpenes, (−)-13(15)E,16E-3β,4β-Epoxy-18-hydroxysphenoloba-13(15),16-diene and (−)-13(15)Z,16E-3β,4β-Epoxy-18-hydroxysphenoloba-13(15),16-diene, by Use of the Ring Closing Metathesis Reaction Applied to Seven-Membered Carbocycles with a Trisubstituted Double Bond

Seven-membered cyclic compounds possessing trisubstituted double bonds have been effectively constructed employing the Grubbs catalyst to effect olefin metathesis. The keto ester does not undergo cyclization; however, alcohols protected by the silyl groups smoothly cyclized into seven-membered compounds. The product was successfully converted to (-)-13(15)E,16E-3beta,4beta-epoxy-18-hydroxysphenoloba-13(15),16-diene and (-)-13(15)Z,16E-3beta,4beta-epoxy-18-hydroxysphenoloba-13(15),16-diene, liverwort diterpenes isolated from Anastrophyllum auritum to establish the absolute configuration.