Enantioselective Bromocyclization of Tryptamines Induced by Chiral Co(III)-Complex-Templated Brønsted Acids under an Air Atmosphere.

The chiral Co(III)-complex-templated Brønsted acids were found to be efficient bifunctional phase-transfer catalysts for the highly enantioselective bromocyclization of protected tryptamines with readily available N-bromosuccinimide (NBS) under an air atmosphere. The 3-bromohexahydropyrrolo[2,3- b]indoles, which are key building blocks of cyclotryptamine alkaloids, were thus obtained in up to 95% yield and 93.5:6.5 er.