Synthesis of contorted nanographenes via multi-fold alkyne benzannulation reactions
AdvisorChalifoux, Wesley A.
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Nanographenes (NGs) of unique shape, size and properties are always at the center of attraction because of their potential application as semiconducting materials in organo-electronic devices. Contorted NGs have gained increased attention because of their fascinating molecular packing, reduced π-π interaction, enhanced solubility and lower band gap compared to the planar analogues. We have synthesized a library of contorted NGs by utilizing the non-oxidative, alkyne benzannu-lation reaction catalyzed by indium chloride and silver bis triflimide by exploiting high energy content of carbon-carbon triple bonds of the diyne precursors under a mild-reaction conditions. We employed two-fold InCl3/AgNTf2-catalyzed alkyne benzannulation reaction to afford a broad collection of highly functionalized, laterally π-expanded, helicene-like naphtho[1,2-a]pyrene derivatives in moderate to very good yields. We were able to utilize this method to expand conju-gation of the HBC core to get a variety of π-extended HBC NGs. The Suzuki cross-coupling of the halogen(s) substituted smaller polycyclic aromatic hydrocarbons with diyne boronic ester gave polyalkyne precursors, which were subjected to multi-fold alkyne benzannulation reaction to af-ford larger, highly soluble contorted NGs. This work also proved the applicability InCl3 and AgNTf2 in the synthesis of up to six benzene ring in one-pot reaction condition. In most of the cases, the chiral, helically twisted skeletons were unambiguously determined through X-ray crys-tallography. We are also very close (two-steps away) towards the synthesis of longer pyrenacenes such as quateropyrene and quinteropyrene following our previous protocol for the synthesis of pyrene, peropyrene and teropyrene.