Chapter 16, Problem 68IP

Interpretation Introduction

Interpretation:

A mechanism should be proposed for the given transformation.

Concept introduction:

• Cycloaddition reaction is a concerted addition reaction of two reactants to form a ring; in which two π-bonds are converted to two σ-bonds.
• Diels-Alder reaction is a $\left[\text{4+2}\right]\text{ cycloaddition}$ reaction, in which a π-system having four atoms (diene) and a π-system having two atoms (dienophile) are undergoing in cycloaddition reaction and producing a substituted cyclohexene.
• The mechanism of the ring formation in the Diels-Alder reaction is drawn by using three arrows representing the shifting of π-bonds in the two π-systems in a clockwise or counter clockwise fashion, so that the ring formation will take place.
• Retro-Diels Alder reaction of a Diels-Alder product is an inverse process of Diels-Alder reaction. It will give the diene and dienophile used for the Diels-Alder reaction.  
• The mechanism of the Retro-Diels Alder reaction for the Diels-Alder product is drawn by using three arrows representing the shifting of one-π-bond and conversion of two σ-bonds to two π-bonds in the Diels-Alder product in a clockwise or counter clockwise fashion, so that the diene and dienophile will form.

To propose: a mechanism for the given transformation.

#assumes the Diels Alder and Retro-Diels Alder reactions are involved in the given transformation.