Cationic Cobalt(III) Catalyzed Indole Synthesis: The Regioselective Intermolecular Cyclization of N-Nitrosoanilines and Alkynes

The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N‐nitrosoanilines with alkynes for the expedient synthesis of N‐substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta‐substituted N‐nitrosoanilines. Moreover, internal alkynes bearing electron‐deficient groups, which are almost unreactive in the [Cp*RhIII]‐catalyzed system, display good reactivity in this transformation. Cp* and Co.: The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N‐nitrosoanilines with alkynes for the expedient synthesis of a variety of N‐substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta‐substituted N‐nitrosoanilines. Cp*=C5Me5.