Chapter 24, Problem 24.52P

Interpretation Introduction

(a)

Interpretation:

The retro Diels–Alder mechanism and product for the given compound shown here is to be drawn.

Concept introduction:

The Diels–Alder reaction joins a conjugated diene and a dienophile (either an alkene or an alkyne) via the formation of two new σ bonds. The product is a six-membered ring of carbon atoms. The Diels–Alder reaction is concerted that is all bonds that are formed and broken do so simultaneously. It requires the cyclic movement of electrons, so it is classified as a pericyclic reaction. Under normal conditions, Diels–Alder reactions tend to be irreversible and proceed under kinetic control. At high temperatures, though, some can undergo the reverse reaction — This is called as a retro Diels–Alder reaction or $\left[\text{4 + 2}\right]$ cyclo elimination. The mechanism for this reaction is simply the reverse of a Diels–Alder mechanism, so the entire reaction consists of a single (concerted) step in which six electrons move in a cyclic fashion.

Interpretation Introduction

(b)

Interpretation:

The retro Diels–Alder mechanism and product for the given compound shown here is to be drawn. Which retro Diels–Alder reaction would require the lower temperature and why so is to be explained.

Concept introduction:

The Diels–Alder reaction joins a conjugated diene and a dienophile (either an alkene or an alkyne) via the formation of two new σ bonds. The product is a six-membered ring of carbon atoms. The Diels–Alder reaction is concerted that is all bonds that are formed and broken do so simultaneously. It requires the cyclic movement of electrons, so it is classified as a pericyclic reaction. Under normal conditions, Diels–Alder reactions tend to be irreversible and proceed under kinetic control. At high temperatures, though, some can undergo the reverse reaction — This is called as a retro Diels–Alder reaction or $\left[\text{4 + 2}\right]$ cyclo elimination. The mechanism for this reaction is simply the reverse of a Diels–Alder mechanism, so the entire reaction consists of a single (concerted) step in which six electrons move in a cyclic fashion.