Chapter 9 - Sigmatropic Rearrangements 2: [i,j] Shifts

Abstract

This chapter describes the [i,j] sigmatropic rearrangements with particular emphasis on [3,3] and [2,3] sigmatropic rearrangements. The [3,3] Cope rearrangement and its variants are presented with reference to relative rates and stereochemical outcome. The fluxional molecules belonging to degenerate Cope systems and antara/antara Cope rearrangement are included. The [3,3] Claisen rearrangement and its important variants, that is, Johnson–Claisen, Eschenmoser–Claisen, Ireland–Claisen and Carroll rearrangements are discussed. The features of stereospecificity and stereoselectivity, endocyclic and exocyclic substrates, asymmetric Claisen rearrangement and aromatic Claisen rearrangement are described. Examples of other [3,3] rearrangements including the Overman reaction and Fischer indole synthesis are also provided. The [2,3] sigmatropic rearrangements are described in anionic and neutral ylide and sulphoxide systems. The [2,3] Wittig rearrangement is presented with particular reference to the stereoselectivity of the process. The [2,3] Stevens rearrangement of sulphur and nitrogen ylides, and Sommelet–Hauser rearrangement are included. The Mislow rearrangement of allyl sulphoxide, its synthetic utility and Meisenheimer rearrangement of allyl N-oxide are described. Finally the higher order and periselective sigmatropic rearrangements are presented.