Abstract
Regarding all the green aspects of sustainable chemical transformations, eco-friendly processes along with economic development, environmental protection as well as natural resources preservation are mandatory. The use of unconventional media for organic transformations has been part of the quest for new eco-friendly process. As new alternative media for volatile organic solvents, deep eutectic solvents (DES) can be defined as the eutectic mixtures formed of two or more phase-immiscible components, which furnish a new homogeneous liquid phase with lower freezing point than those observed for individual counterparts. They found applications in several different fields, such as solvent/catalyst for organic transformations, biotransformations, and polymerization reactions, metal and biomass processing applications, and separation technologies. This review describes the recent studies on the use of deep eutectic mixtures as solvent and/or catalyst for multicomponent reactions in the synthesis of complex organic compounds.
Highlights
Over the last decades, the principles of Green Chemistry have been successfully embraced by the scientific community and the awareness of environmental issues regarding chemical processes is considered as mandatory
In this contribution we focus on the published studies in which deep eutectic mixtures are used as both solvent and/or catalyst in multicomponent reactions based on nucleophilic addition to imines or enamines, Knoevenagel condensation, nucleophilic attack of isocyanides to carbonyl compounds and related processes
The complete replacement of volatile organic compounds (VOCs) in these organic transformations is not a realistic task and more attention should be paid to the life cycle assessment of the solvents involved in all procedure steps, i.e., reaction, washings, purification, etc.[11]
Summary
The principles of Green Chemistry have been successfully embraced by the scientific community and the awareness of environmental issues regarding chemical processes is considered as mandatory. Multicomponent reactions (MCRs) are defined as organic transformations involving three or more starting materials combining together in a single step to afford a product in which all atoms of the starting materials (or at least most of them) are incorporated into its structure.[36] They are highly atom-efficient reactions with environmental friendly procedures, as only a catalytic amount of simple inorganic acids or bases is often required. Another important feature of such multiple-bond-forming transformations is the high degree of molecular complexity and diversity that can be achieved in a single step. The use of deep eutectic solvents in multicomponent reactions has not been fully and critically reviewed, despite the fact it was mentioned as part of some general review on the topic DES.[21,22,56] in this contribution we focus on the published studies in which deep eutectic mixtures are used as both solvent and/or catalyst in multicomponent reactions based on nucleophilic addition to imines or enamines, Knoevenagel condensation, nucleophilic attack of isocyanides to carbonyl compounds and related processes
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