Deep eutectic solvents (DES) have emerged as promising solutions in many areas of chemistry. DES have many of the advantages of ionic liquids (e.g., low vapor pressure, nonflammability, tunability, etc.) but have lower costs, straightforward syntheses, and are often biodegradable. In this minireview, we discuss briefly the applications of DES in areas such as biotransformations, organocatalysis, and combinations of these that lead to multistep processes. DES can be used as solvents, cosolvents, performance additives for bio‐ and organocatalysis, tools to anchor organocatalysts selectively, or for extraction/separation. Several DES have been used both as solvents and organocatalysts at the same time. Given their promising features, it may be expected that many applications in these areas will appear in the coming years.

Biogenic furans (furfural and 5-hydroxymethylfurfural) are expected to become relevant building blocks based on their high degree of functionality and versatility. However, the inherent instability of furans poses considerable challenges for their synthetic modifications. Valorization routes of furans typically generate byproducts, impurities, wastes, and a cumbersome downstream processing, compromising their ecological footprint. Biocatalysis may become an alternative, given the high selectivity of enzymes, together with the mild reaction conditions applied. This Review critically discusses the options for enzymes in the upgrading of furans. Based on previous reports, a variety of biocatalytic transformations have been applied to furans, with successful cases both in aqueous and in water-free media. Options comprise the biodetoxification of toxic furans in hydrolysates, selective syntheses based on oxidation-reduction processes, solvent-free esterifications, or carboligations to afford C derivatives. Reported strategies show in general promising but still modest productivities (2-30 g L d , depending on the example). There are opportunities with high potential and deserving of further development, scale-up, and technoeconomic assessment, to entirely validate them as realistic alternatives.

The use of deep eutectic solvent (DES)/water mixtures were explored for the selective enzymatic synthesis of α‐monobenzoate glycerol (α‐MBG) from glycerol and benzoic acid as substrates. Experiments were performed with four DES, three of them containing choline chloride (ChCl), combined with urea (URA), glycerol (GLY), and ethylene glycol (ETA) (in all cases ChCl/HBD 1:2 mol ratio), and another one formed with methylammonium chloride and glycerol (MA/GLY 1:3 mol ratio). The best conversions (99 %) were achieved with immobilized lipase B from Candida antarctica (CAL‐B) when ChCl/GLY was used as the solvent and the substrate at the same time. The use of water as a cosolvent (8 % v/v) led to a significant decrease in the viscosity of the DES, and full conversions were then reached. Reusability studies of the biocatalyst revealed a 37 % decrease in activity after the first batch, but the activity remained mostly constant for the rest of the cycles.

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Enzyme catalysis (biocatalysis) is a mature strategy to perform organic synthesis with high selectivity and under mild reaction conditions. However, despite their origin and biodegradability, the simple use of enzymes is not sufficient to validate a process as green or sustainable. To reinforce the value that biocatalysis may offer, enzymatic processes can be established in environmentally‐friendly media, such as water, neoteric solvents (e. g. deep‐eutectic‐solvents, DES), biogenic solvents (e. g. 2‐MeTHF or terpenes), or even solvent‐free systems (if substrates allow that). Furthermore, these options can be conducted in continuous biocatalytic processes, which are more efficient and sustainable. Hence, a triple synergy is generated, and very promising environmentally‐friendly options can be envisaged. This conceptual paper discusses these alternatives, providing relevant, recently reported, successful examples.

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