SYNTHETIC STUDIES ON PASPALINE: LEWIS ACID-MEDIATED SEQUENTIAL CONSTRUCTION OF A-E RING SKELETON

The common pentacyclic skeleton of indole diterpene alkaloids, paspaline and its derivatives was constructed by a sequential reaction. The appropriate choice of the protecting group on the indole nitrogen was critical for the formation of bis(methylthio)allylic alcohol, which then underwent sulfonium ion formation and intramolecular electrophilic C-C-bond formation at the indole 3-position.