Here, we report a regioselective, samarium(II) diiodide mediated intramolecular radical ipso-substitution cyclization. Through the use of a methoxy group as a leaving group, it was possible to regulate the regioselectivity of the reaction by changing the temperature and additives. We applied the developed reaction to the synthesis of four Amaryllidaceae alkaloids and have shown that the present reaction successfully overcomes regioselectivity issues encountered with other cyclization methods.
Keywords: Amaryllidaceae alkaloid; natural product synthesis; pyrrolophenanthridinone skeleton; radical ipso-substitution; regioselective cyclization; samarium diiodide.