Chapter 28, Problem 28.27P

Interpretation Introduction

Interpretation:

When the compounds A and B in the previous problem are irradiated, two stereoisomeric compounds, C and D, respectively, are obtained, each of which contains a cyclobutene ring. The structure for C and D, and their formation is to be explained. The irradiation of either A or B does not give back previtamin D2 – the statement is to be verified.

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.