GREEN ALTERNATIVES FOR THE SYNTHESIS OF TETRAZOLIC ACIDS

Abstract

Tetrazolic acids (5-substituted 1H-tetrazoles) are of great interest due to their bioisosterism with carboxylic acids, which accounts for plethora of their pharmacological activities and medicinal applications. Many reports deal with the synthesis of tetrazolic acids using different reactions and synthetic methods. This review intends to summarize most of the green approaches available for obtaining these heterocycles. The starting point in the discussion is the application of multicomponent reactions for the construction of structurally diverse products. However, the most commonly used reaction to afford tetrazolic acids is 1,3-dipolar cycloaddition of azide ion to nitriles. Hence, transition from homogeneous catalysis employed in the early examples of this method to heterogeneous catalysis applying recoverable reagents is highlighted. Similarly, the quest for eco-friendly reaction medium is thoroughly described stressing the use of novel systems like ionic liquids and deep eutectic solvents, reactions in aqueous medium, and solvent-free conditions. Further discussion emphasizes the advantages offered by solid-phase synthesis and nonconventional microwave-assisted reactions. Finally, several examples of successful combinations of different green tactics in a same experimental procedure are presented. Thereby, this article aims to provide the main trends for achieving synthesis of tetrazolic acids using environmentally benign procedures reported in the literature while giving perspectives of possible future advances in this topic.