Xanthate-Based Radical Addition/Spirocyclization on C2-Substituted Tryptamine-Derived Isonitriles

A metal-free protocol for constructing spiroindolines via a radical cascade process is reported. The reaction cascade comprises a radical intermolecular addition to a tryptamine-derived isonitrile, followed by spirocyclization of the intermediate radical onto the C-3 position of the indole system, and concluding with a final oxidation step. Introducing a malonyl or acetoxyl group at the C-2 position of the indole system, along with the addition of a radical bearing an electron-withdrawing group, facilitated the formation of the enamide products. The use of the xanthate-mediated chemistry enabled the generation of primary and secondary electrophilic radicals derived from esters, nitriles, ketones, and lactones.