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3-Isothiocyanato oxindoles are a class of important building blocks which have been widely used in the synthesis of structurally diverse enantioenriched spirooxindoles. In this short review, it is attempted to cover the recent synthetic aspects of 3-isothiocyanato oxindoles participated cascade cyclizations in the last few years (i.e., from 2017 to 2022), with an emphasis on formal [3+2] cycloaddition reactions.1 Introduction2 Organocatalyzed Formal [3+2] Cycloaddition of 3-Isothiocyanato Oxindoles3 Lewis Acid Catalyzed Formal [3+2] Cycloaddition of 3-Isothiocyanato Oxindoles4 Conclusions

A simple and efficient system for the hydration and α-deuteration of nitriles to form amides, α-deuterated nitriles, and α-deuterated amides catalyzed by a single pincer complex of the earth-abundant manganese capable of metal-ligand cooperation is reported. The reaction is selective and tolerates a wide range of functional groups, giving the corresponding amides in moderate to good yields. Changing the solvent from tert-butanol to toluene and using D2O results in formation of α-deuterated nitriles in high selectivity. Moreover, α-deuterated amides can be obtained in one step directly from nitriles and D2O in THF. Preliminary mechanistic studies suggest the transformations contributing toward activation of the nitriles via a metal-ligand cooperative pathway, generating the manganese ketimido and enamido pincer complexes as the key intermediates for further transformations.

International audience; Glycolic acid is a useful and important α-hydroxy acid that has broad applications. Herein, we report the homogeneous ruthenium catalyzed reforming of aqueous ethylene glycol to generate glycolic acid as well as pure hydrogen gas, without concomitant CO2 emission. This approach provides a clean and sustainable direction to glycolic acid and hydrogen, based on inexpensive, readily available and renewable ethylene glycol using 0.5 mol% of catalyst. In-depth mechanistic experimental and computational studies highlight key aspects of the PNNH-ligand framework involved in this transformation.

Separation technology is central to industries as diverse as petroleum, pharmaceuticals, mining and life sciences. Metal–organic cages, a class of molecular containers formed via coordination-driven self-assembly, show great promise as separation agents. Precise control of the shape, size and functionalization of cage cavities enables them to selectively bind and distinguish a wide scope of physicochemically similar substances in solution. Extensive research has, thus, been performed involving separations of high-value targets using coordination cages, ranging from gases and liquids to compounds dissolved in solution. Enantiopure capsules also show great potential for the separation of chiral molecules. The use of crystalline cages as absorbents, or the incorporation of cages into polymer membranes, could increase the selectivity and efficiency of separation processes. This Review covers recent progress in using metal–organic cages to achieve separations, with discussion of the many methods of using them in this context. Challenges and potential future developments are also discussed. This Review discusses recent progress in the uses, challenges and future prospects for separations using metal–organic cages. Precise control over the size, shape and functionalization of these cages enables their application for separations required in petroleum, pharmaceuticals, mining and life sciences.

Liquid organic hydrogen carriers (LOHCs) are powerful systems for the efficient unloading and loading molecular hydrogen. Herein, a liquid-to-liquid organic hydrogen carrier system based on reversible dehydrogenative coupling of ethylene glycol (EG) with ethanol catalysed by ruthenium pincer complexes is reported. Noticeable advantages of the current LOHC system is that both reactants (hydrogen-rich components) and the produced esters (hydrogen-lean components) are liquids at room temperature, and the dehydrogenation process can be performed under solvent and base-free conditions. Moreover, the hydrogenation reaction proceeds under low hydrogen pressure (5 bar), and the LOHC system has a relatively high theoretical gravimetric hydrogen storage capacity (HSC>5.0 wt %), presenting an attractive hydrogen storage system.

This research was supported by the European Research Council (ERC AdG 692775). D. M. holds the Israel Matz Professorial Chair of Organic Chemistry. A. K. is thankful to the Planning and Budgeting Committee of Israel and Feinberg Graduate School for a (senior) postdoctoral fellowship. Y.-Q. Z. acknowledges the Sustainability and Energy ResearchInitiative (SAERI) foundation for a research fellowship. Computations were performed using HPC resources from GENCI-CINES (Grant 2019 AP010811227). The widespread crisis of plastic pollution demands discovery of new and sustainable approaches to degrade robust plastics such as nylons. Using a green and sustainable approach based on hydrogenation, in the presence of a ruthenium pincer catalyst at 150 oC and 70 bar H2, we report here the first example of hydrogenative depolymerization of conventional, widely used nylons, and polyamides in general. Un-der the same catalytic conditions, we also demonstrate the hydrogenation of a polyurethane to produce diol, diamine and methanol. Additionally, we demonstrate an example where monomers (and oligomers) obtained from the hydrogenation process can be dehydrogenated back to a poly(oligo)amide of approximately similar molecular weight, thus completing a closed loop cycle for recycling of poly-amides. Based on the experimental and DFT studies, we propose a catalytic cycle for the process that is facilitated by metal-ligand cooperativity. Overall, this unprecedented transformation, albeit at the proof of concept level, offers a new approach towards a cleaner route to recycling nylons. Publisher PDF

A sustainable, new synthesis of oxalamides, by acceptorless dehydrogenative coupling of ethylene glycol with amines, generating H2, homogeneously catalyzed by a ruthenium pincer complex, is presented. The reverse hydrogenation reaction is also accomplished using the same catalyst. A plausible reaction mechanism is proposed based on stoichiometric reactions, NMR studies, X-ray crystallography as well as observation of plausible intermediates., Ruthenium catalyzed acceptorless dehydrogenative coupling of ethylene glycol and amines to oxalamides is reported. The reverse hydrogenation reaction is also accomplished.

Here we demonstrate how the hydrogen-bonding ability of a BINOL-based dialdehyde subcomponent dictated the stereochemical outcome of its subsequent self-assembly into one diastereomeric helicate form when bearing free hydroxy groups, and another in the case of its methylated congener. The presence of methyl groups also altered the self-sorting behavior when mixed with another, short linear dialdehyde subcomponent, switching the outcome of the system from narcissistic to integrative self-sorting. In all cases, the axial chirality of the BINOL building block also dictated helicate metal center handedness during stereospecific self-assembly. A new family of stereochemically pure heteroleptic helicates were thus prepared using the new knowledge gained. We also found that switching from FeII to ZnII, or the incorporation of a longer linear ligand, favored heteroleptic structure formation.

A recent work published in Science by Cramer and co-workers demonstrates chiral cyclometalated Ir(III) complexes can selectively catalyze the hydrogenation of carbon-nitrogen double bond of oximes with the aid of acid. Various oximes can be hydrogenated to the corresponding N-alkoxy amines in good to excellent yields with good enantioselectivity.

International audience; Hydrogen has long been regarded as an ideal alternative clean energy vector to overcome the drawbacks of fossil technology. However, the direct utilization of hydrogen is challenging, due to low volumetric energy density of hydrogen gas and potential safety issues. Herein, we report an efficient and reversible liquid to liquid organic hydrogen carrier system based on inexpensive, readily available and renewable ethylene glycol. This hydrogen storage system enables the efficient and reversible loading and discharge of hydrogen using a ruthenium pincer complex, with a theoretical hydrogen storage capacity of 6.5 wt%.

Summary Soft materials have found uses in many areas, such as medicine, robotics, and battery research. These advances are the result of the properties of gels stemming from both their solid-like and their liquid-like features. However, fine-tuning of these properties and an onset of new applications can be envisaged if gels are coupled to metal-organic cages, discrete three-dimensional structures containing well-defined cavities. In this perspective, we review the types of cage-gel smart materials synthesized to date, their properties, and their potential applications, such as in molecular separation, catalysis, and luminescent materials. Finally, we highlight current challenges and opportunities for future research.

Visible-light photocatalysis is a rapidly developing and powerful strategy to initiate organic transformations, as it closely adheres to the tenants of green and sustainable chemistry. Generally, most visible-light-induced photochemical reactions occur through single-electron transfer (SET) pathways. Recently, visible-light-induced energy-transfer (EnT) reactions have received considerable attentions from the synthetic community as this strategy provides a distinct reaction pathway, and remarkable achievements have been made in this field. In this Review, we highlight the most recent advances in visible-light-induced EnT reactions.

Mechanical twisting of amides is anticipated to enhance their reactivity considerably. Recent work published in Nature Chemistry by Fujita and co-workers demonstrates that reactive non-planar amide conformers can be bound inside a self-assembled coordination cage. The twisted amides are stabilized by the rigid cavity of the cage and are thus up to 14 times more reactive toward hydrolysis under basic conditions.

[Image: see text] Deoxygenative hydrogenation of amides to amines homogeneously catalyzed by a complex of an Earth-abundant metal is presented. This manganese-catalyzed reaction features high efficiency and selectivity. A plausible reaction mechanism, involving metal–ligand cooperation of the manganese pincer complex, is proposed based on NMR studies and relevant stoichiometric reactions.

An unprecedented phototandem catalysis based on a single iridium photocatalyst has been successfully developed. This powerful strategy consists of two mechanistically distinct catalytic cycles, namely, photocatalytic energy transfer (ET) and single electron transfer (SET). The novel protocol allows a rapid and efficient construction of biologically and synthetically important 3-ester-3-hydroxy-2-oxindole derivatives from readily available diazoamides through a cyclization/aerobic oxidation sequence under very mild conditions.

An efficient halocyclization of β,γ-unsaturated hydrazones with N-bromosuccinimide was developed without the addition of any additives under mild reaction conditions to provide facile access to biologically important 4,5-dihydropyrazoles. Under the optimized conditions, a variety of highly substituted 4,5-dihydropyrazole derivatives were obtained in generally good yields. Moreover, this reaction can be further applied to the synthesis of pyrazoles in a one-pot fashion.

The formyloxylation reaction of 3-bromooxindoles with water and N,N-dimethylformamide (DMF) has been developed in the presence of the photoredox catalyst fac-Ir(ppy)3 under irradiation of visible light at ambient temperature. The reaction provides a straightforward approach to pharmaceutically and synthetically useful 3-formyloxyoxindoles in high yields. The mechanism of this transformation was investigated by fluorescence quenching experiments, “on–off” switching of the light source, labeling experiments, mass spectral analyses and in situ IR experiments.

Diazo compounds have proven to be a useful class of carbenes or metal carbenoids sources under thermal, photochemical, or metal-catalyzed conditions, which can subsequently undergo a wide range of synthetically important transformations. Recently, asymmetric photocatalysis has provoked increasing research interests, and great advances have been made in this discipline towards the synthesis of optically enriched compounds. In this context, the past two decades have been the most productive period in the developments of enantioselective photochemical reactions of diazo compounds due to a better understanding of the reactivities of diazo compounds and the emergence of new catalytic modes, as well as easier access to and treatment of stabilized diazo compounds. This review highlights these impressive achievements according to the reaction type, and the general mechanisms and stereochemical inductions are briefly discussed as well.

A visible light-induced, aerobic oxyamidation reaction of indoles, using air as the sole oxidant, has been developed. This process serves as a photocatalytic strategy to generate efficiently tetrahydro-5H-indolo[2,3-b]quinolinols, which may have interesting biological and pharmacological activities owing to their privileged indoline structure.

Warm mix asphalt (WMA) has been gaining increasing popularity in recent years due to energy savings and environmental benefits. Warm mix asphalt reduces the production temperatures (mixing and compaction) while maintains the advantages of hot mix asphalt (HMA). It is becoming an attractive paving material. Therefore, it is important to understand the rheological behavior of asphalt binders changes with temperature and proportion of the additives. In this study, rheological properties of one commonly used binder PG 70-28 were evaluated, with and without additives (Sasobit® and Aspha-Min®) as the warm asphalt additives, by means of conventional tests as well as dynamic mechanical analysis using Dynamic Shearing Rheometer (DSR).The rheological test included viscosity, temperature sweep and frequency sweep.

A formal [3+2] cycloaddition involving the organocatalytic asymmetric Michael addition/cyclization cascade reaction of ylideneoxindoles with isothiocyanato oxindoles was developed. This method allows efficient and rapid synthesis of highly functionalized bispirooxindole products bearing three contiguous stereogenic centers with two quaternary stereocenters in almost quantitative yields with extremely high enantio- and diastereoselectivities.

An enantioselective tandem Friedel–Crafts alkylation/ Michael addition reaction of 1-methylindoles with nitroolefin enoates catalyzed by a chiral tridentate bisoxazoline-Zn(II) complex has been described. This method provides an efficient route to highly substituted chromans in good isolated yields with high stereoselectivities (up to 95:5 dr and 91% ee).

A highly diastereoselective and regioselective [2+2]-cycloaddition reaction of 3-ylideneoxindoles has been accomplished using visible light photocatalysis. This visible light photocatalytic protocol allows an expedient access to diversely functionalized and structurally constrained oxindole derivatives containing two spirocycles and four stereogenic centers, including two all-carbon quaternary centers.

The photocatalytic reaction occurs in 2 steps and NBS is added to improve efficiency and selectivity.

A Ph3P-catalyzed (3+2) cycloaddition of 2-phenyl-4- arylidene-5(4H)-oxazolones with benzyl 2,3-butadienoate has been developed for the efficient synthesis of structurally diverse and con- formationally constrained aspartic acid analogues.

Asymmetric Michael addition reactions of aldehydes to nitroolefins have been successfully initiated by a series of primary amine thiourea bifunctional catalysts, with high enantioselectivities (90–98% ee) and excellent yields (80–96%). The privileged quinine scaffold was found to be essential to the reaction efficiency and enantioselectivity.

A visible-light-induced photocatalytic aerobic oxidation/[3+2] cycloaddition/aromatization cascade between secondary amines and isocyanides has been successfully developed. The reaction provides a general and efficient access to diversely substituted imidazoles and imidazo[1,5-a]quinoxalin-4(5 H)-ones in good yields under mild conditions.

An unprecedented three-component coupling reaction of arynes, α-bromo carbonyl compounds, and DMSO triggered by insertion of arynes into the S═O bond of DMSO has been developed. The reaction can generate a wide range of multisubstituted aryl methyl thioethers in good yields, wherein DMSO serves as both methylthiolation reagent and oxygen source.

The first example of sequence catalysis by merging visible light photoredox catalysis and nucleophilic catalysis is reported.

An unprecedented three-component coupling reaction of arynes, α-bromo carbonyl compounds, and DMSO triggered by insertion of arynes into the S═O bond of DMSO has been developed. The reaction can generate a wide range of multisubstituted aryl methyl thioethers in good yields, wherein DMSO serves as both methylthiolation reagent and oxygen source.

A visible-light-induced photocatalytic aerobic oxidation/[3+2] cycloaddition/aromatization cascade between secondary amines and isocyanides has been successfully developed. The reaction provides a general and efficient access to diversely substituted imidazoles and imidazo[1,5-a]quinoxalin-4(5 H)-ones in good yields under mild conditions.

Sequence catalysis merging photoredox catalysis (PC) and nucleophilic catalysis (NC) has been realized for the direct sp(3) C-H acroleination of N-aryl-tetrahydroisoquinoline (THIQ). The reaction was performed under very mild conditions and afforded products in 50-91% yields. A catalytic asymmetric variant was proved to be successful with moderate enantioselectivities (up to 83 : 17 er).

A visible light-induced, aerobic oxyamidation reaction of indoles, using air as the sole oxidant, has been developed. This process serves as a photocatalytic strategy to generate efficiently tetrahydro-5H-indolo[2,3-b]quinolinols, which may have interesting biological and pharmacological activities owing to their privileged indoline structure.

The title reaction allows the rapid construction of bispirooxindole skeletons bearing three contiguous stereogenic centers with two quaternary stereocenters in almost quantitative yields and with extraordinarily high enantio- and diastereoselectivities.

An enantioselective tandem Friedel–Crafts alkylation/ Michael addition reaction of 1-methylindoles with nitroolefin enoates catalyzed by a chiral tridentate bisoxazoline-Zn(II) complex has been described. This method provides an efficient route to highly substituted chromans in good isolated yields with high stereoselectivities (up to 95:5 dr and 91% ee).

Title reaction provides access towards structurally constraint spirooxindoles bearing four contiguous stereocenters in excellent diastereoselectivity.

The presented approach provides a facile access to a new family of polyfunctionalized spirooxindoles bearing three consecutive stereogenic centers.