Hoesch reaction

The reaction is a type of Friedel-Crafts acylation with hydrogen chloride and a Lewis acid catalyst.

The synthesis of 2,4,6-Trihydroxyacetophenone (THAP) from phloroglucinol is representative:[1] If two-equivalents are added, 2,4-Diacetylphloroglucinol is the product.

The attacking electrophile is possibly[2] a species of the type R-C+=NHCl−.

The arene must be electron-rich i.e. phenol or aniline type.

The first step is a nucleophilic addition to the nitrile with the aid of a polarizing Lewis acid, forming an imine, which is later hydrolyzed during the aqueous workup to yield the final aryl ketone.