The Allylic Trihaloacetimidate Rearrangment

Overman, Larry E.; Carpenter, Nancy E.


Sigmatropic rearrangements of allylic systems have found wide application in organic synthesis, with carbon-carbon bond forming rearrangements such as the Cope and Claisen rearrangements being particularly well known. The sigmatropic rearrangement of allylic imidates offers a valuable entry into the preparation of protected allylic amines. Conversion of an imidate to the amide is essentially irreversible, with the transformation of the imidate to the amide being exothermic by about 15‚ÄČkcal/mol. Since the discovery of the thermal allylic imidate rearrangement in 1937, a number of systems have been investigated for the practical preparation of allylic amines by this route. However, it was the discovery and development of the rearrangement of allylic trichloroacetamidates that demonstrated the utility of this synthetic method.

This chapter is limited to the discussion of allylic trichloro- and trifluoracetamidate rearrangements. The [3,3]-sigmatropic rearrangement of trichloracetamidates (now called the Overman rearrangement) or trifluoroacetimidates can be carried out either thermally or with Hg(II) or Pd(II) catalysis, The scope of this rearrangement is such that primary, secondary, and tertiary allylic amides are readily accessible, thus providing a wide entry into nitrogen-containing products such as amino sugars, nucleotides, peptides, etc. The Overman rearrangement has found extensive application in the total synthesis of natural products. The recent development of the use of chiral Pd(II) catalysts bodes well for amine synthesis.