LAUSR

Friedel-Crafts acyl rearrangements in PPA of diacetylpyrenes (80–120 °C), dibenzoylpyrenes (80–200 °C), and bis(4-flurobenzoyl)pyrenes (80–120 °C) and Scholl reactions in AlCl 3 /NaCl of dibenzoylpyrenes (140–200 °C) have been studied. The substrates were 1-AcPY , 2-AcPY, 1,3-Ac 2 PY , 1,6-Ac 2 PY , 1,8-Ac 2 PY ,  2,7-Ac 2 PY , 1-BzPY , 1,6-Bz 2 PY , 1,8-Bz 2 PY , 1-4FBzPY , 1,6-4FBz 2 PY , 1,8-4FBz 2 PY . The mixtures of pyrene, 1-AcPY , 2-AcPY , 1,3-Ac 2 PY , 1,6-Ac 2 PY , 1,8-Ac 2 PY , and 2,7-Ac 2 PY were separated by HPLC. The following reversible intermolecular isomerizations were established: 1,6-Ac 2 PY ⇌ 1,8-Ac 2 PY , 1,6-Bz 2 PY ⇌ 1,8-Bz 2 PY , and 1,6-4'FBz 2 PY ⇌ 1,8-4'FBz 2 PY , albeit not in high yields. The results substantiate Gore’s 1955 proposition that “ The Friedel–Crafts acylation reaction of reactive aromatic hydrocarbons is a reversible process .” The isomerizations reported here differ from the few previously reported completely reversible intramolecular Friedel-Crafts acyl rearrangements. At ≥ 140 °C, in PPA and in AlCl 3 /NaCl, 1,6-Bz 2 PY and 1,8-Bz 2 PY underwent a highly regioselective double Scholl reaction to give pyranthrone ( 3 ) and deacylations to 1-BzPy (and pyrene), followed by mono-Scholl reactions to give 8 H -dibenzo[ def,qr ]chrysen-8-one ( 1 ), and 11 H -indeno[2,1- a ]pyren-11-one ( 2 ). The formation of 3 and not the expected tribenzo[ a,ghi,o ]perylene-7,16-dione ( 4 ) from 1,8-Bz 2 PY indicates that 1,8-Bz 2 PY has first undergone isomerization to 1,6-Bz 2 PY . The present study confirms the linkage between Friedel-Crafts acyl rearrangements and the Scholl reaction.