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Complexity‐increasing Domino reactions comprising C−H allenylation, a Diels–Alder reaction, and a retro‐Diels–Alder reaction were realized by a versatile catalyst derived from earth‐abundant, non‐toxic manganese. The C−H activation/Diels–Alder/retro‐Diels–Alder alkyne annulation sequence provided step‐economical access to valuable indolone alkaloid derivatives through a facile organometallic C−H activation manifold with transformable pyridines.