I₂‑DMSO-Mediated N–H/α-C(sp³)–H Difunctionalization of Tetrahydroisoquinoline: Formal [2 + 2 + 1] Annulation for the Construction of Pyrrolo[2,1‑a]isoquinoline Derivatives

An I₂-DMSO-mediated cascade reaction using methyl ketones and 1,2,3,4-tetrahydroisoquinolines (THIQs) as commercially available substrates has been developed for the construction of pyrrolo­[2,1-a]­isoquinoline derivatives. This metal-free process involves N–H/α-C­(sp³)–H difunctionalization of THIQ. Two C–C bonds and one C–N bond are formed in one pot under mild conditions. Besides, a quaternary carbon center has been constructed in this transformation efficiently.