CuI-catalyzed cascade cyclization using indole-3-carbaldehydes and amidines for the synthesis of pyrimido[4,5-b]indoles.

We report a copper-catalyzed cascade cyclization for the concise synthesis of pyrimido[4,5-b]indole skeletons via direct C-H functionalization and concomitant C-N bond formation. This methodology utilizes an inexpensive catalytic system (CuI/2,2'-bipyridine). The reaction demonstrates remarkable functional group tolerance and consistently delivers the target heterocycles in good to excellent yields. The insights gained from our studies are expected to advance general efforts towards the efficient synthesis of biology-oriented privileged heterocyclic skeletons.