Programmable zigzag π-extension toward graphene-like molecules by the stacking of naphthalene blocks

Graphene-like molecules with a zigzag periphery are interesting because of their ability to host spin-polarized electronic edge states. Although progress has been made for the preparation of armchair-edged graphene-like molecules, a general synthetic strategy to zigzag type remains elusive. Herein, using acetylenedicarboxylates as the C2 insertion unit, we report a rapid and modular strategy to extend the pi-conjugation in a zigzag fashion through a rhodium-catalysed sequential C2-H and C8-H activation-annulation of naphthalene ketones. Different from the reported C-H activation-annulation of aryl ketones with alkynes to form a five-membered indenol, fulvene or six-membered pyran oxonium, this [4 + 2] and [4 + 2] annulation sequence selectively undergoes C(sp3)-H cyclization to extend the naphthalene fragment. This programmable zigzag pi-extension can be compared to the stacking of toy blocks, as the naphthalene fragments are added step by step along an alkyl chain, demonstrated by the synthesis of anthanthrene and subsequently peri-naphthacenonaphthacene. These products are easily transformed to electron transport materials and thermally activated delayed fluorescent materials. Graphene-like molecules with a zigzag periphery are synthetically challenging. Now, a programmable zigzag pi-extension strategy to rapidly assemble graphene-like molecules is reported based on rhodium-catalysed sequential C2-H and C8-H activation-annulation of naphthalene ketones, using acetylenedicarboxylates as the C2 insertion unit.