The synthesis of hydroxy-pyrrolizidines and indolizidines from cyclopropenones: towards hyacinthacines, australines and jenamidines

The reaction of cyclic imines (1-pyrrolines and piperideines) with a cyclopropenone leads to pyrrolizidines and indolizidines, respectively, each with a hydroxy group on the carbon atom at the bridgehead. The cyclopropenone functions as an all-carbon 1,3-dipole equivalent towards the cyclic imine in this reaction, and the cyclic imines used include polyhydroxylated systems, thus allowing access to australine, alexine and hyacinthacine type compounds. The pyrrolizidine products contain the core of the jenamidine and bohemamine natural products, which are of interest as cell-proliferation inhibitors and cell–cell adhesion inhibitors.