The multicomponent reactions (MCRs) consist of two or more synthetic steps which are carried out without isolation of any intermediate thus reducing time, saving money, energy and raw materials. The development of MCRs in the presence of molecular iodine is an efficient approach that meets with the requirements of sustainable chemistry. The aim of this review is to highlight the synergistic effect of the combined use of MCRs and molecular iodine for the development of new eco-compatible methodologies for organic chemistry.

A convenient and efficient method for synthesis of substituted 2,4,6-triarylpyridines by the reaction of chalcones and ammonium acetate or via one-pot, three-component condensation of aromatic aldehydes with acetophenones and ammonium acetate has been developed by using the efficient catalyst PEG₁₀₀₀-based dicationic acidic ionic liquid (PEG₁₀₀₀-DAIL) under solvent-free conditions. Recycling studies have shown that the PEG₁₀₀₀-DAIL can be readily recovered and reused several times without significant loss of activity. GRAPHICAL ABSTRACT

A novel and green approach for efficient and rapid synthesis of 4-aryl-3-methyl-1-phenyl-1H-benzo[h]pyrazolo[3,4-b]quinoline-5,10-diones has been accomplished by the one-pot condensation reaction of aromatic aldehydes, 3-methyl-1-phenyl-1H-pyrazol-5-amine and 2-hydroxynaphthalene-1,4-dione using PEG₁₀₀₀-based dicationic acidic ionic liquid (PEG₁₀₀₀-DAIL) as a catalyst was reported. Recycling studies have shown that the PEG₁₀₀₀-DAIL can be readily recovered and reused several times without significant loss of activity. The key advantages are the short reaction time, high yields, simple workup, and recovered catalyst.

An efficient procedure has been researched for the solvent-free synthesis of bis(indolyl)methanes via a one-pot reaction of indoles and aldehydes or ketones promoted by PEG₁₀₀₀-based dicationic acidic ionic liquid (PEG₁₀₀₀-DAIL). The catalyst PEG₁₀₀₀-DAIL could be reused seven times with excellent results. Furthermore, through this method, a highly chemoselective reaction of benzaldehyde and acetophenone with indole could be achieved.

PEG₁₀₀₀-based dicationic acidic ionic liquid (PEG₁₀₀₀-DAIL) was found to be an efficient and recyclable catalyst for Mannich-type reaction of different ketones with various aromatic aldehydes and aromatic amines in water to give various β-arylamino ketones in good yields. The catalytic system could be easily recovered and reused for at least six runs only with slight decrease in its activity. GRAPHICAL ABSTRACT

A series of 3-arylbenzoquinoline, pyranoquinoline, and thiopyranoquinoline derivatives have been synthesized by one-pot, multicomponent reaction of aromatic aldehyde, naphthalen-2-amine, and ketone using polyethylene glycol (PEG₁₀₀₀)–based dicationic acidic ionic liquid as recyclable catalyst with high yields. The PEG ionic liquid and toluene have the advantages of both homogeneous and heterogeneous phases at different temperatures (biphasic conditions at lower temperatures and monophasic at higher temperatures) with the ease of product as well as catalyst separation. Recycling studies have shown that the ionic liquid can be readily recovered and reused several times without significant loss of activity.