the rearrangement. Chen–Mapp reaction The Chen–Mapp reaction, also known as the [3,3]-phosphorimidate rearrangement or Staudinger–Claisen reaction, installs a phosphite in the place of an alcohol and takes advantage of the Staudinger reduction to convert this to an imine. The subsequent Claisen is driven by the fact that a P=O double bond is more energetically favorable than a P=N double bond. Overman rearrangement The Overman rearrangement (named after Larry Overman) is a Claisen rearrangement of allylic trichloroacetimidates to allylic trichloroacetamides. The Overman rearrangement is applicable to the synthesis of vicinol diamino compounds from 1,2-vicinal allylic diols. Zwitterionic Claisen rearrangement Unlike typical Claisen rearrangements which require heating, zwitterionic Claisen rearrangements take place at or below room temperature. The acyl ammonium ions are highly selective for Z-enolates under mild conditions. In nature The enzyme chorismate mutase (EC 5.4.99.5) catalyzes the Claisen rearrangement of chorismate to prephenate, an intermediate in the biosynthetic pathway towards the synthesis of phenylalanine and tyrosine. History Discovered in 1912, the Claisen rearrangement is the first recorded example of a [3,3]-sigmatropic rearrangement. See also Carroll rearrangement Cope rearrangement References Rearrangement reactions Name reactions Substitution reactions Carbon-carbon bond forming reactions