L-Proline: A Versatile Organo-Catalyst in Organic Chemistry

Background: L-proline is a natural amino acid having secondary amine functionality and acts as a bifunctional catalyst (organo-catalyst). The amino-functional group acts as Lewis base type while carboxylic acids act as Brønsted acid type catalysts. It catalyzed different asymmetric syntheses, including known reactions such as Aldol condensation, Mannich reaction, Michael Addition, Knoevenagel condensation, Hantzsch synthesis, OXA-Michael Henry tandem, Ullmann reactions, Wieland-Miescher ketone synthesis, Robinson annulation, Biginelli reaction, α- amination. It is also an essential catalyst for synthesizing heterocyclic skeletons such as coumarin, spiro-oxindoles, imidazoles, benzimidazoles, quinoxalines, podophyllotoxin, benzothiazoles, isoxazolidines, phenothiazines, aziridine, indole, 1,5-benzodiazepines, pyridine, and quinazolines. Objective: In this review, we had the objective to critically summarize the use of proline and proline derivatives as catalysts of multicomponent reactions performed in various media and leading to synthetically and biologically relevant heterocycles, a very important class of compounds that constitutes over 60% of drugs and agrochemicals. Methods: All scholarly articles for L-Proline catalyzed reactions were retrieved from ScienceDirect, Google Scholar , PubMed, etc. Results and Conclusion: Given the importance of L-Proline based reactions, it has been observed to have tremendous applications in organic chemistry. It can also act as a 'Green catalyst'.