Future developments in molecular carbon nanoscience will hinge on the availability of versatile synthetic strategies that enable rational control of properties. Since the majority of nanocarbons are comprised of fused rings, polycyclic aromatic hydrocarbons (PAHs) can be viewed both as the smallest nanocarbons and as building blocks for their macromolecular congeners (e.g. graphene nanoribbons and carbon nanotubes). The major synthetic challenge is the fusion of many rings, which requires regioselective formation of many C–C bonds. Very few methods have found general use in this regard, and most provide unfunctionalized products or cannot easily produce analogues. This thesis develops an efficient and versatile ring-fusion platform, based on a final-step [2+2+n] cycloaddition, which also enables divergent production of functionalized analogues. The work presented herein not only puts the large number of known [2+2+n] cycloadditions into a unified conceptual framework for strategic application to conjugated nanocarbons, but also contributes new reactions to the toolbox.

Chapter 1 introduces the general features of the synthetic platform, which can be conceptually broken up into three steps: 1) modular synthesis of an oligo-diyne or -dinitrile precursor; 2) ring-fusion via metal-mediated cyclization; and 3) divergent, “post-fusion” functionalization. Steps 2 and 3, which together make up a formal [2+2+n] reaction, can usually be performed in the one pot or make up part of a catalytic cycle. Chapters 2–7 chronicle the development of the synthetic strategy via its target-driven application to synthetically challenging nanocarbons. Some targets have a storied history (e.g. arylene ethynylene macrocycles and cycloarenes) and others are previously unknown (e.g. expanded helicenes and their macrocyclic derivatives), but all are inaccessible using previous approaches.