Electrocyclic Reactions: Introduction

From a historical point of view, electrocyclic reactions and their remarkable stereospecificity in particular gave rise to the development of the concept of pericyclic reactions and the Woodward-Hoffmann rules in the early 60s. Electrocyclic reactions are characterized by the fact that a linear conjugated π system cyclizes by forming a σ bond.

As is the case with all pericyclic reactions, electrocyclic reactions pass through an aromatic transition state. The reaction is reversible with ring opening favored in 3- and 4-membered rings (reduction in ring strain).