VilsmeierHaackFormylierung

The Vilsmeier-Haack reaction is a chemical process used to introduce an aldehyde group into an aromatic ring or activated alkene. It is named after the German chemists Anton Vilsmeier and Albrecht Haack. The reaction typically involves the use of a phosphoryl chloride (POCl3) or thionyl chloride (SOCl2) in combination with a substituted amide, most commonly N,N-dimethylformamide (DMF). This combination generates the electrophilic Vilsmeier reagent, which is a chloromethyleniminium salt.

The Vilsmeier reagent then attacks the electron-rich aromatic or olefinic substrate. Following nucleophilic attack, a series of steps involving hydrolysis leads to the formation of the desired aldehyde. The reaction is particularly useful for the formylation of electron-rich aromatic compounds such as phenols, anilines, and pyrroles. It can also be applied to certain heterocyclic compounds. The Vilsmeier-Haack reaction is a valuable tool in organic synthesis for the preparation of various aldehydes, which are important intermediates in the synthesis of pharmaceuticals, dyes, and other fine chemicals. Its mild reaction conditions and good yields make it a popular choice for many synthetic chemists.