A sequential cyclization/π-extension strategy for modular construction of nanographenes enabled by stannole cycloadditions |
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Authors: | Harrison M Bergman D Dawson Beattie Gavin R Kiel Rex C Handford Yi Liu T Don Tilley |
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Institution: | Department of Chemistry, University of California, Berkeley California 94720 USA.; Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley California 94720 USA, |
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Abstract: | The synthesis of polycyclic aromatic hydrocarbons (PAHs) and related nanographenes requires the selective and efficient fusion of multiple aromatic rings. For this purpose, the Diels–Alder cycloaddition has proven especially useful; however, this approach currently faces significant limitations, including the lack of versatile strategies to access annulated dienes, the instability of the most commonly used dienes, and difficulties with aromatization of the 4 + 2] adduct. In this report we address these limitations via the marriage of two powerful cycloaddition strategies. First, a formal Cp2Zr-mediated 2 + 2 + 1] cycloaddition is used to generate a stannole-annulated PAH. Secondly, the stannoles are employed as diene components in a 4 + 2] cycloaddition/aromatization cascade with an aryne, enabling π-extension to afford a larger PAH. This discovery of stannoles as highly reactive – yet stable for handling – diene equivalents, and the development of a modular strategy for their synthesis, should significantly extend the structural scope of PAHs accessible by a 4 + 2] cycloaddition approach.Stannoles are introduced as a new, spontaneously aromatizing diene for 4 + 2] cycloadditions that can be easily introduced into diverse conjugated systems, facilitating the efficient synthesis of complex PAHs and their π-extension. |
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