Carbon cages that entrap metals were first observed just days after the landmark discovery of C₆₀. The synthesis of Sc₃N@C₈₀, which is comprised of a planar Sc₃N cluster encapsulated within an icosahedral C₈₀ cage, transformed significantly the field of endohedral metallofullerenes (EMFs). Recently, efficient routes toward arc discharge plasma synthesis of EMFs by vaporization of graphite, metal oxide, and solid nitrogen sources, such as guanidine thocyanate and guanidinium salts, have been developed. However, the origin of EMFs produced by plasma synthesis techniques and any associated formation processes that take place remains still unclear. Here, we report some recent results on the gas-phase synthesis of Sc₃N@C_2n and particularly on the transformation of the pentalene-containing Sc₃N@D₃-C₆₈ compound, which transform through a bottom-up mechanism into Sc₃N@C₈₀. We will discuss on potential pathways for the growth of Sc₃N@D₃-C₆₈ when it is exposed to an atmosphere of carbon plasma produced from graphite, and on the potential role that heptagonal rings may play.