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Diels-Alder reactivity of polycyclic aromatic hydrocarbon bay regions: implications for metal-free growth of single-chirality carbon nanotubes.

A soluble bisanthene derivative, 4,11-dimesitylbisanthene, has been synthesized in three steps from bianthrone. In hot toluene, this bisanthene undergoes a clean Diels-Alder reaction with diethyl acetylenedicarboxylate to give a rearomatized 1:1 cycloadduct and, more slowly, a rearomatized 2:1 cycloadduct. In a competition experiment with the shorter "periacene" perylene, only the bisanthene reacts, and the perylene remains unchanged. The experimental results stand in complete accord with density functional calculations (B3LYP/6-31G*), which predict that the activation energies for Diels-Alder cycloadditions in the bay regions of periacenes should diminish monotonically as the length of the molecule increases. This structure-activity relationship offers hope that single-chirality carbon nanotubes can be grown from suitable hydrocarbon templates, without metal catalysis, by a Diels-Alder cycloaddition/rearomatization strategy, using acetylene or a "masked acetylene" as the dienophile.