Palladium-catalysed routes to the tricyclic core of the Stemona alkaloids

The Stemona alkaloids are a structurally interesting class of alkaloids isolated from the roots and rhizomes of the Stemonaceae plant family. During this project we have investigated the viability of constructing the tricyclic core of the Stemona alkaloids using a cascade Heck/carbopalladation reaction sequence, starting from an allylvinylcyclopropane building block, utilising the group's [2+3] palladium catalysed cycloaddition chemistry. [Illustration omitted.] We have briefly investigated applying our palladium catalysed [2+3] cycloaddition methodology towards doubly activated vinylcyclopropanes, preparing a selection of tetrahydrofuran and pyrrolidine precursors which underwent a Heck mediated cyclisation to yield a variety of functionalised polycycles. As well as further developing this methodology towards a tandem cycloaddition/Heck one-pot strategy. [Illustration omitted.] We have also investigated applying this methodology towards the construction of the azepine core of the Stemoamide group of Stemona alkaloids. Using the group's [2+3] cycloaddition chemistry to construct suitable pyrrolidines and subjecting them to Heck mediated cyclisations as well as investigating the viability of a tandem cycloaddition/Heck one-pot strategy.