Chapter 28, Problem 28.39AP

Interpretation Introduction

Interpretation:

The following sigmatropic reaction is to be classified and the curved-arrow notation is to be given, the stereochemistry is that expected for a thermal concerted reaction is to be shown.(This reaction, discovered by Prof. J. A. Berson at Yale University, was the first example of this type of pericyclic reaction.)

Concept introduction:

Sigmatropic reaction can be described as the migration of allylic sigma bond at one end of the π-electron system to the other end of the π-electron system as an uncatalyzed intramolecular reaction. In some cases, Lewis acid catalysts can also be applied. Though, the position of π-bond is changed in Sigmatropic reaction, the total number of π-bonds remain unchanged. The sigma bond can be cleaved at the middle or at the end of the π-system. The formation of sigma bond at 3, 3-position of a 1, 5-diene is called as cope rearrangement.