Synthesis of 2‐Pyrazolines from Hydrazines: Mechanisms Explained

Abstract 2‐Pyrazoline core is a very interesting five‐membered heterocycle, which has been explored in recent years due to its vast applications as the core structure of bioactive and industrial agents. Based on literature studies, versatile synthetic approaches have been employed for the preparation of 2‐pyrazolines, among them the reaction between hydrazines and α,β‐unsaturated enones as the most used method. In this review article, different methods for the synthesis of 2‐pyrazolines using hydrazine derivatives were classified and presented. Initially, numerous catalytic methods for the preparation of 2‐pyrazolines from hydrazines and α,β‐unsaturated enones are reviewed and various aspects of these methods discussed including catalyst efficiency, catalyst recovery, green chemistry, cost‐effectiveness, scope of the method, enantioselectivity, and yield. In addition, reactions between hydrazines and other reagents in multicomponent and two‐component reactions, developed recently, are discussed. Finally, some of the important applications of 2‐pyrazolines are summarized.