Lewis acid-mediated synthesis of pyrido[1,2-a]indoles via 1,2-aryl/alkyl migration-aromatization of fused 3-oxindoles.

We report a mild and metal-free Lewis acid-mediated strategy for the synthesis of pyrido[1,2-a]indoles via a 1,2-aryl/alkyl migration-aromatization cascade of fused 3-oxindoles derived from spiro-oxindoles through ring-closing metathesis (RCM). The transformation proceeds under simple conditions (TMSOTf, DCE, 60 °C), affording a broad range of products in good yields with excellent functional group tolerance. The resulting compounds exhibit emission in the 530-635 nm range, depending on the migratory group, providing access to structurally diverse, biologically relevant, and emissive pyrido[1,2-a]indole derivatives.