ijsigmatropic
ij-sigmatropic rearrangements, usually written as [i,j]-sigmatropic, are a class of pericyclic reactions in organic chemistry in which a sigma bond migrates across an adjacent or remote conjugated π-system. This migration reorders bonding without adding or removing atoms. The indices i and j indicate the span of the π-system that the migrating fragment traverses between the two ends of the sigma bond, and they determine the type of rearrangement. Common examples include [1,5]-sigmatropic shifts and the widely studied [3,3]-sigmatropic rearrangements.
Mechanistically, these processes are typically concerted, proceeding through cyclic transition states that couple sigma- and pi-electron
Notable examples include the [3,3]-sigmatropic rearrangements known as the Cope rearrangement (in 1,5-dienes) and the Claisen
Overall, ij-sigmatropic rearrangements are important tools in organic synthesis for constructing complex carbon frameworks and for