Deep eutectic solvents (DESs) have emerged as an alternative to ionic liquids (ILs). DESs share with ILs some appealing features, such as low vapor pressure, capability to dissolve reagents insoluble in common organic solvents, and the possibility to tune the overall pH of the medium by replacing one of the constituents of the mixture. Furthermore, DESs can be prepared by combining molecules that come from natural sources (i.e., glycerol, glucose), making them biodegradable. DESs have already been used for a variety of reactions and protocols since they were reported for the first time by A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed and V. Tambyrajah, Chem. Commun., 2003, 70, and among the reactions studied, organic oxidation has recently gained much attention. In particular, the recyclability of these ionic compounds makes it possible to achieve anchoring of organic oxidants, such as TEMPO and peroxydisulfate, directly onto one species of the DES mixture components. In addition, their solubility properties play a crucial role in organic oxidation since DESs have the ability to dissolve both organic lipophilic and hydrophilic species, making the oxidation of organic compounds mediated by hydrogen peroxide more efficient. Herein we report the state of the art of this developing field, focusing on the benefits of substituting common organic solvents with DESs, especially in terms of sustainability, enhancement of reactivity, and recyclability.

In-depth analysis of structure/activity relationship aids rational design of modified carbon nitride for organophotocatalysis.

Chemistry in continuous-flow continues to attract attention from the community of synthetic organic chemists due to its now well-recognized benefits including, inter alia, quick reaction times, operational safety, rapid reaction screening/optimization, enhanced automation with possible addition of in-line reaction analysis, and easy scalability. Coupling of flow chemistry to enabling technologies (e.g. unconventional solvents, supported reagents or catalysts, microwave irradiation, photochemistry, inductive heating, microreactors) as well as to additive manufacturing (AM) technologies (i.e. 3D printing) gives additional advantages for throughput and automation, and besides this, unique opportunities are offered by compartmentalization, that allows multistep syntheses to occur reconciling incompatible reaction conditions. Based on all this, continuous-flow may itself be seen as an enabling technology which leads in the direction of process intensification meeting increasingly pressing sustainability issues (e.g. waste minimization, cost/energy reduction). As part of flow chemistry, organocatalysis represents an active research area under which there is large opportunity for re-optimizing long-standing reactions or inventing new transformations. Both homogeneous (soluble) and heterogeneous (insoluble) organic molecules have been used as catalysts for continuous-flow processing in either achiral or asymmetric fashion, any issue inherent to a homogeneous approach (high catalyst loading, difficult catalyst separation) being typically overcome with the use of heterogenized organocatalysts. This review is aimed at covering the progresses on organocatalysis in continuous-flow from 2016 to early 2020, with special attention paid to the comparison between batch and flow processes for each discussed transformation to substantiate the potential of flow technology for process intensification.

The application of the oxidative system composed of a heterogeneous triazolium pre-catalyst, iron(II) phthalocyanine and air is described for the selective conversion of 5-hydroxymethylfurfural (HMF) into the added-value 5-hydroxymethyl-2-furancarboxylic acid (HMFCA). The disclosed one-pot two-step procedure involved sequential oxidative esterifications of HMF to afford a polyester oligomer having hydroxyl and carboxyl terminal groups (M_w = 389–1258), which in turn was hydrolyzed by a supported base (Ambersep 900 OH) to yield HMFCA in 87% overall yield. The same strategy was adopted for the effective synthesis of ester and amide derivatives of HMFCA by nucleophilic depolymerization of the oligomeric intermediate with methanol and butylamine, respectively. The utilization of the disclosed oxidative system for the direct conversion of HMF and furfural into their corresponding ester, amide, and thioester derivatives is also reported.

N‐Heterocyclic carbene (NHC) catalysis is a by now consolidated organocatalytic platform for a number of synthetic (asymmetric) transformations via diverse reaction modes/intermediates. In addition to the typicalumpolungprocesses involving acyl anion/homoenolate equivalent species, implementation of protocols under oxidative conditions greatly expands the possibilities of this methodology. Oxidative NHC‐catalysis allows for oxidative and oxygenative transformations through specific manipulations of Breslow‐type species depending upon the oxidant used (external oxidant or O₂/air), the derived NHC‐bound intermediates paving the way to non‐umpolungprocesses through activation of carbon atoms and heteroatoms. This review is intended to update the state of the art in oxidative NHC‐catalyzed reactions that appeared in the literature from 2014 to present, with a strong focus to crucial intermediates and their mechanistic implications.