Radical Cyclisation Reactions Leading to Polycyclics Related to the Amaryllidaceae and Erythrina Alkaloids

Novel radical cyclisation reactions, mediated by tributyltin hydride, samarium(II) iodide or manganese(III) acetate, have been explored to form tri- and tetra-cyclic ring systems related to the Amaryllidaceae or Erythrina family of alkaloids. Haloethanamide precursors possessing a cyclohexenone ring have been shown to form octahydroindolones, and erythrinane-type systems can be formed from precursors bearing unsaturated side-chains in tandem cyclisations. An octahydroindolone has been converted to the ring skeleton of γ-lycorane using samarium(II) iodide while reaction with manganese(III) acetate has been shown to yield a novel tetracyclic ring system bearing a 7-membered ring. Finally, a new tandem cyclisation of a cyclohexenone aryl halide has been shown to provide a quick approach to a 5,5,6,6-tetracycle related to erythrinane natural products.