Chapter 28, Problem 28.26P

Interpretation Introduction

Interpretation:

When previtamin D₂ is heated, two compounds, A and B, are obtained that are stereoisomers of both ergosterol and lumisterol. Structures for these compounds, and their formation is to be explained.

Concept introduction:

Generally, electrocyclic reactions are a pericyclic reaction which occur intramolecularly. These reactions will result in the formation of ring compounds under the influence of heat or light. Notably, in this process one new sigma bond is formed and one old π-bond is consumed. Intriguingly, the reverse ring opening electrocyclic reaction can also be possible to occur under the same reaction mechanism but in reverse manner. In-phase orbital overlap results in symmetry allowed electrocyclic reactions.