Organocatalyzed cycloaddition reactions of azomethine imines—A lookback

Abstract

The versatile and convergent nature of 1,3‐dipolar cycloaddition reactions has made them an indispensable tool in organic chemistry for synthesizing five‐membered heterocycles. Among the various dipoles, azomethine imines (AMI) constitute a versatile class, increasingly used to synthesize biologically relevant heterocycles. The organocatalytic cycloaddition reactions of azomethine imines are relatively unexplored compared to the corresponding transition metal‐catalyzed reactions. This review highlights the unique organocatalytic cycloaddition reactions of AMI with different dipolarophiles. The cycloaddition of azomethine imines catalyzed by organic bases such as prolinol, proline, alkaloids, 1,4‐diazabicyclo[2.2.2]octane, 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), primary amines, tertiary amines, N‐heterocyclic carbene, and phosphine are discussed here. The mechanistic and electronic aspects, including broad functional group tolerance, catalyst loading, and reaction conditions, are evaluated. This review also demonstrates the scope and potential reactivity of azomethine imines in organocatalytic cycloadditions. We are positive that the reactions of azomethine imines discussed here will aid in discovering new and efficient reaction pathways in synthesizing biologically active and industrially relevant molecules.