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. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim