Cascade radical-mediated cyclisations with conjugated ynone electrophores. An approach to the synthesis of steroids and other novel ring-fused polycyclic carbocycles

Abstract

A cascade radical-mediated Diels–Alder reaction with the iododienynone 16b produced the tricyclic ketone17 (22%). By contrast, treatment of the substituted furans36 and 47 with Bu₃SnH–AIBN, instead led to the tetracycles 44 and 58 respectively, rather than the anticipated oestranes, i.e.38 and 48. In a separate study, attempted cascade radical-mediated cyclisations from the ortho-aryl substituted iododienynones 72 and 73, leading to the ring-D aromatic steroid7, instead gave the macrocyclic ketone76 or the novel bridged tricycles 77/82, respectively, depending on whether benzene or heptane was used as solvent in the reactions.