Molecular nanocarbons are critical bridges between small polycyclic aromatic hydrocarbons and extended graphene lattices, driving advances across materials science, optoelectronics, and quantum technologies. However, the atomically precise synthesis of such systems, particularly those featuring K-region and cove-type topologies, remains an enduring challenge. Here, we present a de novo modular strategy that overcomes this constraint by directing K-region growth via annulation of preorganized aryl acetylnaphthalene precursors with acetylenedicarboxylate. The strategy mirrors the hierarchical construction of pyrene by formally inserting naphthalene fragments into spatially defined molecular scaffolds. This method integrates Suzuki-Miyaura coupling with a Zn(OTf)2-catalyzed cascade comprising Friedel-Crafts alkylation, dehydro-Diels-Alder cycloaddition, and dehydrogenative aromatization. The platform affords structurally diverse pyrene-based molecular nanocarbons with programmable control over topology and dimensionality, spanning linear, contorted, and three-dimensional π-architectures. These results establish a generalizable blueprint for bottom-up synthesis of complex carbon-rich architectures with atomic precision.