Reversible Friedel-Crafts Acylations of Phenanthrene: Rearrangements of Acetylphenanthrenes

The study of Friedel-Crafts acetylation of phenanthrene with acetic acid in polyphosphoric acid, along with rearrangements and deacetylations of acetylphenanthrene isomers, indicated its reversibility. The structures of (E)-2- AcPHN and (Z)-9-AcPHN were determined by X-ray crystallography. PM3 calculations predicted that 9-AcPHN is the kinetically controlled while 2-AcPHN and 3-AcPHN are the thermodynamically controlled products, in accordance with experiment. The mutual rearrangements of 2-AcPHN and 9-AcPHN are noted.