Ketone Oximes as NO ₂ Radical Precursors for Regioselective Iodo–Nitrosylative Cyclization of Unactivated 1,6-Enynes

A metal-free three-component radical cascade cyclization of unactivated 1,6-enynes has been developed using 1-phenylethan-1-one oxime as a novel in situ nitrogen dioxide (NO₂) radical source under I₂/aqueous TBHP conditions. This transformation proceeds through a chemo- and regioselective sequence involving NO₂· addition to the terminal alkene, 5-exo-dig cyclization onto the alkyne, and iodine trapping of the resulting carbon-centered radical, yielding 4-(iodo(phenyl)methylene)-3-(nitromethyl)-1-tosylpyrrolidines. This strategy avoids transition metals, photocatalysts, or prefunctionalized nitrogen reagents and highlights the previously unexplored potential of oximes as bench-stable NO₂-radical donors for cascade transformations.