Question

In order for the following transformation to occur thermally, what pericyclic reactions must occur?

• A. 1. sigmatropic rearrangement, 2. electrocyclic ring-closing
• B. 1. electrocyclic ring-opening, 2. Diels-Alder
• C. 1. sigmatropic rearrangement, 2. Diels-Alder
• D. 1. electrocyclic ring-opening, 2. electrocyclic ring-closing

Answer 1

The correct option is B 1. electrocyclic ring-opening, 2. Diels-Alder

Firstly, in the presence of heat, electrocyclic-ring opening takes place (there is no possibility of sigmatropic rearrangement) and after ring opening it acts as diene and undergo [4+2] cycloaddition reaction, i.e., Diels-Alder reaction.