[2,3]-Rearrangements of Ammonium Zwitterions

The [2,3]-rearrangements of ammonium zwitterions are useful for the synthesis of nitrogen-containing chiral molecules. These rearrangements have served as key steps in the synthesis of complex natural products, which are discussed in this chapter. The [2,3]-rearrangement of amine N-oxides has become a powerful strategy for the total synthesis of natural products and other complex molecules. From a retrosynthetic perspective, there are several retrons associated with this process. For example, the identification of an O-allylhydroxylamine in the target molecule can guide the utilization of the Meisenheimer rearrangement in a total synthesis. The [2,3]-rearrangement of ammonium ylides has become a general strategy for the total synthesis of natural products and other target molecules. Retrosynthetically, α-allyl acid derivatives are common retrons for this sigmatropic process. Given the ubiquity of noncanonical amino acid substructures in naturally occurring small molecules, the Stevens rearrangement has emerged as a synthetically powerful transformation.