Radical cyclisation reactions leading to polycyclics related to the Amaryllidaceae and Erythrina alkaloids

Novel radical cyclisation reactions, mediated by tributyltin hydride, samar ium(II) iodide or manganese(III) acetate, have been explored to form tri- a nd tetra-cyclic ring systems related to the Amaryllidaceae or Erythrina fam ily of alkaloids. Haloethanamide precursors possessing a cyclohexenone ring have been shown to form octahydroindolones, and erythrinane-type systems c an be formed from precursors bearing unsaturated side-chains in tandem cycl isations. An octahydroindolone has been converted to the ring skeleton of g amma-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 h alide has been shown to provide a quick approach to a 5,5,6,6-tetracycle re lated to erythrinane natural products. (C) 2000 Elsevier Science Ltd. All r ights reserved.