Treatment of 1-acetylanthracene (1-AcAN) and 9-acetylanthracene (9-AcAN) with PPA at 80-120 °C leads to the nearly complete conversion of these isomers into 2-acetylanthracene (2-AcAN), an illustration of the Agranat-Gore rearrangement of polycyclic aromatic ketones (PAKs). Ab initio MP2/6-31(d) calculations predict the following order of stabilities: for -complexes: 9-AcAN > 1-AcAN > 2-AcAN; for ketones: 2-AcAN > 1-AcAN > 9-AcAN; for O-protonated ketones: 2-AcAN > 1-AcAN > 9-AcAN. Thus, 9-AcAN is the kinetically controlled product, whereas 2-AcAN is the thermodynamically controlled product. No reverse rearrangements of 2-AcAN to either 9-AcAN or 1-AcAN and of 1-AcAN to 9-AcAN were observed. The results strengthen the pattern of reversibility in Friedel-Crafts acylations of PAHs.
Keywords: Friedel-Crafts acetylation, PPA, Overcrowding, Agranat-Gore rearrangement, Deacylation, Ab initio calculations
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