Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the “watershed” in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous so...

Catalytic Organic Reactions in Water toward Sustainable Society

Deep eutectic solvents (DESs), also known as deep eutectic ionic liquids (DEILs) or low-melting mixtures (LMMs) or low transition temperature mixtures (LTTMs) in the literature, have become more and more attractive in recent years due to their interesting properties and benefits, such as low cost of components, easy to prepare, tunable physicochemical properties, negligible vapor pressure, non-toxicity, biorenewability and biodegradability. These eutectic mixtures have been widely used as green and sustainable media as well as catalysts in many chemical processes. This review focuses on recent advances using DESs in organic reactions including addition reactions, cyclization reactions, replacement reactions, multicomponent reactions, condensation reactions, oxidation reactions, and reducing reactions.

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Recent advances in the application of deep eutectic solvents as sustainable media as well as catalysts in organic reactions

The scientific community has been seeking cost-competitive and green solvents with good dissolving capacity for the valorization of lignocellulosic biomass. At this point, deep eutectic solvents (DESs) are currently emerging as a new class of promising solvents that are generally liquid eutectic mixtures formed by self-association (or hydrogen-bonding interaction) of two or three components. DESs are attractive solvents for the fractionation (or pretreatment) of lignocellulose and the valorization of lignin, owing to the high solubility of lignin in DESs. DESs are also employed as effective media for the modification of cellulose to afford functionalized cellulosic materials, such as cellulose nanocrystals. More interestingly, biomassderived carbohydrates, such as fructose, can be used as one of the constituents of DESs and then dehydrated to 5-hydroxymethylfurfural in high yield. In this review, a comprehensive summary of recent contribution of DESs to the processing of lignocellulosic biomass and its derivatives is provided. Moreover, further discussion about the challenges of the application of DESs in biomass processing is presented.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cssc.201701012

Green processing of lignocellulosic biomass and its derivatives in deep eutectic solvents

Cellulose dehydration and depolymerization reactions during pyrolysis in the presence of phosphoric acid

Glycals (or usually their O-substituted derivatives) are readily converted into 2,3-unsaturated glycosyl compounds with O-, C-, N-, S- or otherwise linked substituents at the anomeric position. These products have been found to be useful for a range of synthetic purposes. In particular, the C-glycosidic compounds have served as readily available starting materials for the preparation of useful non-carbohydrate compounds. While these allylic rearrangement processes are usually conducted under the influence of Lewis acid catalysts, adaptations that involve activation of the allylic substituents of the starting glycals as leaving groups under neutral conditions have been developed. General features of the reactions are described as well as applications in synthesis and extensions of the basic processes.

Substitution-with-Allylic-Rearrangement Reactions of Glycal Derivatives

Allylic rearrangement of 6-deoxyglycals having practical utility

Stereoselective synthesis of functionalized carbocycles by cycloaddition to levoglucosenone

A mild, efficient and operationally simple one-pot synthesis of substituted [1,2,4]triazolo[4,3-a]pyridines at room temperature from easily available 2-hydrazinopyridine and substituted aromatic aldehydes has been developed. This functional group tolerant and atom-economic method provides facile access to synthetically and biologically important triazolopyridine derivatives.

A facile and practical one-pot synthesis of [1,2,4]triazolo[4,3-a]pyridines

Ninhydrin undergoes an unprecedented condensation reaction with various 2-aminobenzamide derivatives in boiling water to afford 11a-hydroxy-11,11a-dihydrobenzo[e]indeno[2,1-b][1,4]diazepine-10,12-dione derivatives. These hitherto unreported products are easily isolated in high yield by a simple filtration step. An interesting “ortho effect” was observed in the condensation reaction of ninhydrin with 2-amino-N-phenylbenzamide derivatives having an ortho- substituent in the N-phenyl moiety wherein the corresponding expected 3′-phenyl-1′H-spiro[indene-2,2′-quinazoline]-1,3,4′(3′H)-triones were obtained.

A Serendipitous Synthesis of 11a-Hydroxy-11,11a-dihydrobenzo[e]indeno[2,1-b][1,4]diazepine-10,12-dione Derivatives by Condensation of 2-Aminobenzamides with Ninhydrin in Water.

An environmentally benign, one-pot, three component synthesis of annulated pyrroles by coupling free sugars with enamines, generated in situ from aryl amines and 1,3-diketones, has been achieved by using a deep eutectic solvent (DES). The reaction conditions are mild and do not require additional Bronsted or Lewis acid catalysts.

Prakash M. Bhate

Papers

Allylic rearrangement of 6-deoxyglycals having practical utility

Stereoselective synthesis of functionalized carbocycles by cycloaddition to levoglucosenone

A facile and practical one-pot synthesis of [1,2,4]triazolo[4,3-a]pyridines

A Serendipitous Synthesis of 11a-Hydroxy-11,11a-dihydrobenzo[e]indeno[2,1-b][1,4]diazepine-10,12-dione Derivatives by Condensation of 2-Aminobenzamides with Ninhydrin in Water.

Acid- and metal-free synthesis of annulated pyrroles in a deep eutectic solvent