Double C–H Functionalization of Indoles via Three-Component Reactions/CuCl₂‑Catalyzed Aerobic Dehydrogenative Coupling for the Synthesis of Polyfunctional Cyclopenta[<i>b</i>]indoles

A sequential Rh₂(OAc)₄-catalyzed multicomponent reaction and CuCl₂-catalyzed postcyclization process is developed to build polyfunctional cyclopenta­[<i>b</i>]­indoles in good yields with high diastereoselectivities in an atom- and step-economic fashion. The key discovery in this process is the CuCl₂-catalyzed intramolecular aerobic dehydrogenative Csp²–Csp² cross-coupling of indole C2 with an enol functionality. Mechanistic studies including X-ray photoelectron spectroscopy analysis suggest that the catalytic cycle involves Cu­(II) and Cu­(I). This coupling reaction represents a unique example of aerobic Cu-catalyzed direct coupling of indoles with enols under mild conditions