Pyrrole Synthesis via Allylic sp3 C-H Activation of Enamines Followed by Intermolecular Coupling with Unactivated Alkynes

A conceptually novel pyrrole synthesis is reported, efficiently merging enamines and (unactivated) alkynes under oxidative conditions. In an intermolecular Rh catalyzed process, the challenging allylic sp(3) C-H activation of the enamine substrates is followed by the cyclization with the alkyne (R-3 = CO2R). Alternatively, in some cases (R-3 = CN), the enamine can be utilized for a vinylic sp(2) C-H activation. A total of 17 examples with yields above 60% is presented, together with the results of an initial mechanistic investigation.