Tetraxene: Serendipity Leads to a Versatile Three‐Dimensional Building Block

Cyclooctatetraene (COT)‐containing building blocks occupy a unique position in carbon materials, yet their synthesis generally relies on lengthy and low‐yielding approaches. In this study, we report the serendipitous discovery and rational development of tetraxene, a synthetically accessible tetraindene‐fused COT scaffold uncovered during attempts to extend truxene π‐conjugation. Although indanone condensations intrinsically favor thermodynamically reinforced trimer formation, stepwise interception and reactivation of a discrete dimer intermediate redirects the reaction toward selective tetramerization. This two‐step strategy provides concise access to a family of tetraxene derivatives ( 2b–e ) in synthetically useful yields (70%–80%). Single‐crystal x‐ray diffraction reveals a rigid nonaromatic COT core with pronounced bond localization while demonstrating that subtle peripheral modifications profoundly alter solid‐state symmetry, leading to remarkably diverse supramolecular architectures. Beyond its distinctive structural behavior, tetraxene contains orthogonally addressable reactive domains that enable modular functionalization at both the aromatic periphery and the five‐membered rings. These results establish tetraxene as a structurally defined and chemically versatile 3D COT‐based building block and demonstrate that thermodynamically biased aromatic condensation pathways can be deliberately redirected toward higher‐order non‐benzenoid carbon architectures.