The Birch 1,4-reduction of an aromatic ring to its corresponding unconjugated cyclohexadiene, involves an alkali metal dissolved in liquid ammonia in the presence of an alcohol. An electron from the metal interacts with the aromatic ring, resulting in a carbanion and a radical. The carbanion abstracts a proton from the alcohol, and a second electron joins the radical, forming another carbanion, which abstracts a proton from alcohol. If the aromatic ring is substituted, the regioselectivity of the reduction depends on whether the substituent is electron-donating or electron-withdrawing.
- Reagents: Lithium, Sodium or Potassium Metal, Liquid Ammonia, Alcohol
- Reactant: Aromatic Compound
- Product: Unconjugated Cyclohexadiene
- Type of Reaction: Reduction
Lab Tips
- Heterocycles, including pyridines, pyrroles, and furans are also prone to reduction.
- Double bonds present in the molecule that are not conjugated are exempt from reduction.
Mechanism
