The Fries rearrangement uses a Lewis or Brӧnsted acid to synthesize ortho- and/or para substituted phenolic ketones and aldehydes from phenolic esters. How the acyl group migrates to the ring is not yet fully understood, but there is evidence for ionic intermediates. The ortho product is favored at high temperatures and no solvent, while the para product is favored at low temperatures and increasing solvent polarity.

• This reaction requires high temperatures (80-180 ͦ C) and at least one equivalent of the acid; reaction times may vary from a few minutes to several hours.^[1]
• Electron-donating substituents on the phenol promote good yields while electron-withdrawing substituents can result in (very) low yields to no reaction.^[1]
• Alkyl migration is often observed with polyalkylated phenols under these conditions. ^[1]
• Optically active phenolic esters may rearrange to optically active phenolic ketones.^[1]
• At room temperature ortho-lithiated O-aryl carbamates may undergo an intramolecular [1,3]-acyl migration to give substituted salicylamides (called anionic ortho-Fries rearrangement). ^[1]
• Anilides may rearrange to p- or o-aminoaryl ketones and enol esters to β-diketones.^[2]

• Reagents: Lewis or Brӧnsted Acid (HF, HClO₄, PPA) or Solid Acid (e.g. Zeolites) or hv (called Photo-Fries Rearrangement)
• Reactant: Phenolic Ester (Electron-donating groups on the phenol favored)
• Product: Ortho and/or Para Substituted Phenolic Ketones or Aldehydes
• Type of Reaction: Phenol Ester Rearrangement

Mechanism

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Related Compounds