The Johnson-Claisen (also known as the ortho ester Claisen rearrangement) uses catalytic acid and heat to produce a γ,δ-unsaturated ester from an allylic alcohol and excess trialkyl orthoacetate. One of the alkoxy groups of the orthoacetate is first exchanged for the allylic alcohol, followed by an internal proton transfer from the alcohol to an OR group. A molecule of alcohol is then eliminated, yielding an unstable ketene acetal, which undergoes a [3,3]-sigmatropic shift to afford the γ,δ-unsaturated ester product.
- Reagents: Catalytic Acid (Proionic Acid)
- Reactant: Allylic Alcohol, Trialkyl Orthoacetate
- Product: γ,δ-Unsaturated Ester
- Type of Reaction: Rearrangement
Mechanism
