Organocatalytic Enantioselective Transformations: A Green Approach to Cycloaddition and Cyclization Reactions

Organocatalysis has been successfully applied to enantio-selective transformations, as an eco-friendly alternative to metal catalysis, mostly in asymmetric cycloaddition and cyclization reactions which are essential for providing new synthetic routes and an efficient synthesis of chiral frameworks, particularly for drug molecules. Cycloaddition reactions are important for this reason, that they allow the formation of multiple bonds during one reaction and therefore allow the rapid construction of complex structural motifs cyclo-adducts. However, problems such as selectivity control and scalability of the reactions are still problems to be solved. According to this review, the small organic molecules exhibit several benefits of the catalyst operating at ethylene glycol solvent-free environmentally benign mild conditions. Some of the advancements include bifunctional catalytic systems and mechanochemistry which have boosted enantio-selectivity particularly in delicate reactions. Another type of transformations that are reflected cyclization reactions also prove the concept of using organocatalysts and their ability to create the most complex cyclic structural motifs at low temperatures. However, some issues such as recovery of the catalyst, the involvement of water in these reactions, and other factors that put a constraint in scaling up have still been a problem. This implies that more research must be conducted to harness the industrial effectiveness of organocatalysis and to deal with the above drawbacks.