Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Conjugated Systems and Pericyclic Reactions
End of Chapter Problems

1. 18.6 Which of the following molecules is(are) conjugated?

2. 18.7 Predict the product for the Diels—Alder [4+2] reaction given below.

3. 18.8 Complete the following reactions by providing the dienes and dienophiles.

4. 18.9 Give the structures of compounds A and B (including stereochemistry where appropriate) in the reaction sequence shown below, the last step involves a pericyclic reaction.

5. 18.10 For the reaction of diarlysenenoketones with conjugated dienes (shown below), give the major organic product with appropriate stereochemistry.

6. 18.11 For the following pericyclic reactions, give the major organic products. (hint: consider a sigmatropic rearrangement, i.e. Cope and/or Claisen rearrangements)

7. 18.12 The conversion of the reactant to the product shown below involves a sequence of two pericyclic reactions. The first is an electrocyclic ring opening reaction involving the cyclobutene moiety to form an unstable intermediate A. The second reaction involves an intramolecular [4+2] cycloaddition reaction. Give the structure of intermediate A and use arrow-pushing formulism to indicate electron movement to explain how the intermediate A and product are formed.

8. 18.13 For the synthesis of the sex hormone estrone, a sequence of two pericyclic reactions was utilized. The first reaction is an electrocyclic ring opening reaction involving the cyclobutane moiety to form an unstable intermediate A; and the second reaction an intramolecular [4+2] cycloaddition reaction. Give the structure of intermediate A and explain using arrow-pushing formulism to indicate electron movement to explain how the product, estrone, is formed.