Also known as: Vilsmeier-Haack formylation
The Vilsmeier-Haack reaction is an organic reaction used to convert an electron rich aromatic ring to an aryl aldehyde using DMF, an acid chloride, and aqueous work-up. The mechanism begins with the reaction of DMF with the acid chloride to form an iminium salt known as the "Vilsmeier reagent". The electron rich aromatic ring then attacks the iminium ion with loss of aromaticity. A deprotonation step restores aromati-city, which is followed by the release of a chloride ion to form another iminium intermediate. Aqueous work-up then leads to the aryl aldehyde final product.
Vilsmeier, A.; Haack, A. Ber. dtsch. Chem. Ges. 1927, 60, 119–122.