Deep eutectic solvents as reusable catalysts and promoter for the greener syntheses of small molecules: Recent advances

Deep eutectic solvents (DESs) are significant environmentally benign media in the field of green chemistry. They are known not only for their inexpensive nature, biodegradability, non-toxicity, and bioavailability, but also for recyclability and their ease of preparation and purification. DESs are made up of hydrogen bond donor substituents (such as urea, carboxylic acid, glycerol, metals, etc.) and hydrogen bond acceptor substituents such as halide salts; they have a lower melting point than each substituent comprising the mixture. DESs find applications in biotransformation, gas separation, biomass valorization, electrochemistry, extraction, and dissolution process as well as in material chemistry and other assorted fields of chemistry. Interestingly, DESs fulfil a unique dual role as green solvents, promoters and catalysts in organic syntheses. Thus, it is noteworthy that chemical progresses and transformation with external catalysts in cross-coupling reactions, oxidations and reductions are not covered in this overview. This review mostly focuses on leading-edge applications of DES as a reusable catalyst in the expeditious synthesis of assorted small molecules central in the assembly of broad-spectrum pharmaceuticals, and total synthesis of common natural products.