How the carbon skeleton of the given triene must be coiled to give the given product has to be shown. Concept Introduction: Diels-Alder reaction: It is the reaction of conjugated dienes with double or triple bonded compounds which are known as “dienophiles” . The reaction is a 4 + 2 cycloaddition reaction that results in the formation of a six membered cyclic product which is known as “adduct” . Example: This mechanism shown that three π -bonds are broken to form two new σ -bonds and a new π -bond. Intramolecular reaction: In the word “Intramolecular”- “Intra”- means “within” or “in”. So an intramolecular reaction means the reaction is taking place within one molecule itself without the involvement of any other molecules.

Question

Diphenylacetylene can be synthesized by the double dehydrohalogenation of 1,2-dibromo-1,2-diphenylethene. The sequence starting from (E)-1,2-diphenylethene consists of bromination to give the dibromide, followed by dehydrohalogenation to give a vinylic bromide, then a second dehydrohalogenation to give diphenylacetylene.(a) What is the structure, including stereochemistry, of the vinylic bromide?(b) If the sequence starts with (Z)-1,2-dibromo-1,2-diphenylethene, what is (are) the structure(s) of the intermediate dibromide(s)? What is the structure of the vinylic bromide?

Answer 1

Question

Chapter 20, Problem 20.34P

Interpretation Introduction

Interpretation:

How the carbon skeleton of the given triene must be coiled to give the given product has to be shown.

Concept Introduction:

Diels-Alder reaction:

It is the reaction of conjugated dienes with double or triple bonded compounds which are known as “dienophiles”. The reaction is a 4+2 cycloaddition reaction that results in the formation of a six membered cyclic product which is known as “adduct”.

Example:

This mechanism shown that three π-bonds are broken to form two new σ -bonds and a new π-bond.

Intramolecular reaction:

In the word “Intramolecular”- “Intra”- means “within” or “in”. So an intramolecular reaction means the reaction is taking place within one molecule itself without the involvement of any other molecules.

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