Johnson-Claisen Rearrangement

The Johnson-Claisen rearrangement is one of the varieties of Claisen rearrangements and gives γ,δ-unsaturated esters from allyl alcohols and orthoacetates. In this reaction, an allyl alcohol and an orthoacetate react by treatment with an acid and heat to produce a ketene acetal in situ. The ketene acetal rearranges and affords a γ,δ-unsaturated ester, which results in a two-carbon elongation. The Eschenmoser-Claisen rearrangement and Ireland-Claisen rearrangement are similar to the Johnson-Claisen rearrangement when they are used properly according to the proper choice of substrates and conditions.