Johnson-Claisen rearrangement

Also known as: ortho ester Claisen rearrangement

The Johnson-Claisen rearrangement is an organic reaction where an allylic alcohol is heated with trialkyl orthoacetate under midly acidic conditions to produce a γ,δ-unsaturated ester. The reaction begins with protonation of one of the alkoxide groups of the orthoacetate. The protonated alkoxide is then released as a molecule of alcohol and forms an oxonium cation which is then attached by the alcohol. Proton transfer steps then follow, protonating another alkoxide group, that is again lost as alcohol and forms another oxonium cation. A deprotonation step then produces a 1,5 diene intermediate which undergoes a Claisen sigmatropic rearrangement to provide the final γ,δ-unsaturated ester product.^[1]