Anion‐Assisted Sigmatropic Rearrangements

Abstract The use of sigmatropic rearrangements for the synthesis of organic compounds has become one of the important synthetic tools available to the organic chemist, especially since the development of the detailed stereochemical understanding of these processes in terms of orbital symmetry. The flexibility and predictability of the Cope rearrangement make this type of process widely applicable. The interest and synthetic activity related to the Cope rearrangement can be seen in a previous review of the Claisen and Cope rearrangements. In that review, several variations of the rearrangement were discussed, including examples of the “oxy‐Cope” rearrangement. In 1975 examples of an oxy‐Cope rearrangement were reported wherein an enormous rate acceleration (10 15 ) was observed on formation of the potassium salt of the oxy‐Cope substrate. This chapter surveys extensions of this type of anionic substituent effect to other [3,3]‐, [5,5]‐, [1,3]‐, and [1,5]‐sigmatropic rearrangements as well as retro‐[2 + 2] and reverse Diels–Alder reactions. Specifically excluded are the ester enolate Claisen rearrangement which is mechanistically unrelated, the Wittig rearrangement, and the Haller–Bauer reaction. The chemical literature has been searched to the end of 1989. Emphasis is placed on reactions of synthetic utility, novelty, and generality.