The design and synthesis of persistent tetraaryl[4]cumulenes are reported. Derivatives with phenyl endgroups ([4]Ph and [4]Ph/Ar*) are susceptible to reactions during synthesis and/or purification that complicate isolation of the desired product, particularly intermolecular dimerization reactions. Incorporation of (3,5‐di‐tert‐butyl)phenyl endgroups (Ar*) provides increased stability, culminating in the stable and isolable [4]cumulene [4]Ar*. Cumulene [4]Ar* remains, however, susceptible to dimerization under pressing conditions, and [4]Ar* also readily reacts with electrophiles under mild conditions that lead to intramolecular cyclization. Given the structural complexity of the side products in these studies (compounds 3, 10, 14, 17, 18), X‐ray crystallography plays a vital role in their identification. [ABSTRACT FROM AUTHOR]