The Vilsmeier-Haack reaction or Vilsmeier-Haack formylation uses DMF, phosphoryl chloride (POCl3), and water to convert an electron-rich arene to a substituted benzaldehyde. First, DMF and phosphoryl chloride form an iminium salt called the “Vilsmeier reagent”. Then the aromatic compound attacks the Vilsmeier reagent, disturbing its aromaticity. Deprotonation by DMF restores aromaticity, and a chloride ion is released to form an aryl iminium intermediate. Exposure to water affords the final aryl aldehyde.
- Reagents: DMF, Acid Chloride (POCl3, SOCl2, Oxalyl Chloride, etc.), Solvent (Halogenated Hydrocarbon, DMF, or POCl3), Water
- Reactant: Electron-Rich Aromatic or Heteroaromatic Compound
- Product: Substituted Benzaldehyde or Heteroaromatic Aldehyde
- Type of Reaction: Nucleophilic Addition (Vilsmeier Reagent Formation), Electrophilic Aromatic Substitution
- Bond Formation: Ar-C=O
Lab Tips
- Electron-rich alkenes and 1,3-dienes are also suitable substrates for this reaction. [1]
- The relative reactivity of five-membered heterocycles is pyrrole > furan > thiopene. [2]
- The reaction temperature, dependent on the reactivity of the substrate, ranges from below 0°C to up to 80°C. [2]
- Formylation at the less sterically hindered (para) position on a substituted benzene ring is favored. [2] Electronic effects however may also influence product distribution.
2. Kürti, L., Czakó, B. (2005). Strategic Applications of Named Reactions in Organic Synthesis; Background and Detailed Mechanisms. Burlington, MA: Elsevier Academic Press.
Mechanism
Top Citations
Original Paper
Related Compounds
- DMF (CAS 68-12-2)
- Phosphorous Oxychloride (CAS 10025-87-3)
