Fries rearrangement

Schematic of the Fries rearrangement. Reagents: phenyl ester, Lewis acid catalyst, AlCl3, acid work-up. Product: o-hydroxy aryl ketone, p-hydroxy aryl ketone.

The Fries rearrangement is an organic reaction used to convert a phenyl ester to an ortho- and para-hydroxy aryl ketone using a Lewis acid catalyst and Brønsted acid work-up. The mechanism begins with coordination of the ester to the Lewis acid, followed by a rearrangement which generates an electrophilic acylium cation. The aromatic compound then attacks the alkyl cation (both the ortho and para attack are allowed) via an electrophilic aromatic substitution (SEAr). Deprotonation to regenerate aromaticity and Brønsted acid work-up to regenerate the Lewis acid catalyst provide the two hydroxy aryl ketone products.[1][2]

Mechanism

Mechanism of the Fries rearrangement. There are two possible pathways to product.

References:

1.
Fries, K.; Finck, G. Ber. Dtsch. Chem. Ges. 1908, 41, 4271–4284.
2.
Fries, K.; Pfaffendorf, W. Ber. Dtsch. Chem. Ges. 1910, 43, 212–219.