Cobalt(II)/silver relay catalytic isocyanide insertion/cycloaddition cascades: a new access to pyrrolo[2,3-b]indoles.

The combination of Co(acac)2 and AgOTf enables the bimetallic relay catalysis reaction of 2-ethynylanilines and isocyanides, allowing easy and low-cost access to new densely functionalized pyrrolo[2,3-b]indoles. The reaction pathway involves a Co(acac)2-catalyzed double isocyanide insertion followed by a silver-enabled 1,3-dipolar cycloaddition. The synthetic utility of these bicycloaddition reactions results in subsequent C-C and C-N bond-forming events to rapidly build up molecular complexity.