Green Organocascades: Sustainable Strategies for Metal-Free Asymmetric Organic Synthesis

Purely small organic molecules can act as organocatalysts and organocatalysis being superficial, selective, simple, inexpensive and eco-friendly nature has gained great attention over the last years. They are non-toxic, low cost, inert towards air and moisture, ease in catalyst recovery, and amenable to solid support leads to green protocol. Organocatalysts can be classified based on their structure as well as on their activation modes. There are many types of organoctalysts used in Tandem reactions in different conditions. Asymmetric organocatalysts are used which act as chiral promoters and convert the achiral compounds into chiral products while covalent catalysis forms covalent link. The scope of this focused review is to explain different types of organocatalysts which can be used during one pot synthesis with examples such as Lewis acid-base, Bronsted acid-base, Amines, Alkaloids, Prolines, Carbenes and various Chiral compounds. It also describes certain Asymmetric Organocatalytic reactions, a comprehensive detail of the Tandem Michael Reaction and its types, Enantioselective Mannich reaction, Henry reaction and Sequential reaction. The examples of reaction which can be carried out in more sustainable medium such as ionic liquids, deep eutectic solvent, water, alternative green solvents and solvent free conditions using microwaves, ultrasound and high pressure which not only increase the effective yield but also accelerate ease of reaction and product isolation which increase the sustainability of organocatalytic reactions are explained here.