Citric Acid Promoted Green Synthesis of Bioactive Heterocycles

In this review, we report green transformations of biologically active heterocycles catalyzed by Citric acid. Citric acid is found naturally in citrus fruits, especially lemons and limes. Citric acid is soluble in water used as a highly efficient and biodegradable catalyst for multi-component transformations, biomimetic reactions, and C-C bond formation. It has been applicable for the multicomponent synthesis of pyrano[2, 3-e]pyrimidin, pyrano[2, 3-d]pyrazol-amines, amidoalkyl naphthols, tetrahydropyridines, indazolo[2,1-b]phthalazine-triones, indazolo[2,1-b]phthalazine-triones, indazolo[2,1-b]phthalazine-triones, ethyl 3-methyl-4,5-dioxo-1,2-diphenylpyrrolidine-3-carboxylate and 2,4-disubstituted thiazoles from ketones via C–Br, C–S, and C–N Bond Formations. Citric acid is also used in combination with ultrasound for the synthesis of biologically active pyrazolyl-bis coumarinyl methanes and pyrrolidinone. Citric acid is used in the generation of nanocatalysts, mesoporous carbon materials (OMCs) as well as polymerization reactions by the reaction of resorcinol/formaldehyde resin. Citric acid is also used in the generation of fluorescent 1,4-disubstituted-1,2,3-triazoles1,8-dioxo-decahydroacridines by Hantzsch condensation.