π-Radical Cascades to Peri-Fused Triangulene Dimers.

Open-shell molecular graphene fragments represent versatile synthons of graphene-based carbon nanostructures because of their ability to undergo multi-step π-radical cascades that enable the formation of multiple bonds and rings in a single step. However, the use of graphene-based π-radicals in synthesis remains limited due to our incomplete understanding of their reactivity. This limitation primarily arises from the inherent difficulty of controlling reactions involving multiple reactive centers, as is the case with π-delocalized radicals. To address this challenge and advance research on π-radical reactivity, we establish reaction control in a system that can formally feature multiple unpaired π-electrons. Specifically, we examine oxidative peri-fusion of the dihydro-precursor of the prototypic non-Kekulé hydrocarbon triangulene. By investigating the reactive intermediates that dictate selectivity, we demonstrate that monoradical, rather than diradical, intermediates play a key role. Through the precise placement of steric bulk around the periphery, we modulate reactivity at specific positions, steering selectivity toward doubly or singly peri-fused dimeric products. Our study demonstrates that, when controlled, the reactivity of open-shell molecular graphene fragments can serve as a step-economic and synthetically valuable tool.