Synthetic reactions using organometallics in water. Aldol and allylation reactions catalyzed by Lewis acid–surfactant-combined catalysts/Brønsted acids systems

Surfactant-mediated thioglycosylation of 1-hydroxy sugars in water

Thioglycosides are an important class of sugars, since they can be used as non-ionic biosurfactants, biomimetic glycosides, and building blocks for carbohydrate synthesis. Previously, Brønsted- or Lewis-acid-catalyzed dehydrative glycosylations between a 1-hydroxy sugar and a thiol have been reported to yield open-chain dithioacetal sugars as the major products instead of the desired thioglycosides. These dithioacetal sugars are by-products derived from the endocyclic bond cleavage of the thioglycosides. Herein, we report dehydrative glycosylation in water mediated by a Brønsted acid-surfactant combined catalyst (BASC). Glycosylations between 1-hydroxy furanosyl/pyranosyl sugars and primary, secondary, and tertiary aliphatic/aromatic thiols in the presence of dodecyl benzenesulfonic acid (DBSA) provided the thioglycoside products in moderate to good yields. Microwave irradiation led to improvements in the yields and a shortening of the reaction time. Remarkably, open-chain dithioacetal sugars were not detected in the DBSA-mediated glycosylations in water. This method is a simple, convenient, and rapid approach to produce a library of thioglycosides without the requirement of anhydrous conditions. Moreover, this work also provides an excellent example of complementary reactivity profiles of glycosylation in organic solvents and water.

Tartaric Acid–Zinc Nitrate as an Efficient Brønsted Acid-Assisted Lewis Acid Catalyst for the Mannich Reaction

Tartaric acid–zinc nitrate has been found to be an efficient Brønsted acid-assisted Lewis acid catalytic system for the facile synthesis of β-amino carbonyl compounds through the one-pot Mannich reaction of aldehydes, aromatic amines and ketones in ethanol at room temperature. Remarkable enhancement of reactivity by tartaric acid (Brønsted acid) was observed in these reactions in the presence of anhydrous zinc nitrate (Lewis acid), due to coordination of the tartaric acid ligand to zinc ions increasing the acidity of the system. This procedure shows some advantages such as mild reaction conditions, short reaction times and high yields.

Catalytic Organic Reactions in Water toward Sustainable Society

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 solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Alkylidene malonates and α,β-unsaturated α′-hydroxyketones as practical substrates for vinylogous Friedel–Crafts alkylations in water catalysed by scandium(iii) triflate/SDS

Alkylidene malonates and α,β-unsaturated α′-hydroxyketones are excellent substrates for the Sc(OTf)₃/SDS catalysed Friedel–Crafts alkylation in water.

Mukaiyama Aldol Reactions in Aqueous Media

Mukaiyama aldol reactions in aqueous media have been surveyed. While the original Mukaiyama aldol reactions entailed stoichiometric use of Lewis acids in organic solvents under strictly anhydrous conditions, Mukaiyama aldol reactions in aqueous media are not only suitable for green sustainable chemistry but are found to produce singular phenomena. These findings led to the discovery of a series of water-compatible Lewis acids such as lanthanide triflates in 1991. Our understanding on these beneficial effects in the presence of water will be deepened through the brilliant examples collected in this review. 1 Introduction 2 Rate Enhancement by Water in the Mukaiyama Aldol Reaction 3 Lewis Acid Catalysis in Aqueous or Organic Solvents 3.1 Water-Compatible Lewis Acids 4 Lewis-Base Catalysis in Aqueous or Organic Solvents 5 The Mukaiyama Aldol Reactions in 100% Water 6 Asymmetric Catalysts in Aqueous Media and Water 7 Conclusions and Perspective.

High molar mass polymers by cationic polymerisation in emulsion and miniemulsion

The generation of poly(p-methoxystyrene) with a molar mass of several thousand g mol(-1) by cationic polymerisation in emulsion, is described here for the first time. Such a striking result was achieved by carrying out the polymerisation inside monomer droplets, thus preventing fast transfer reactions with water.

Dehydration reactions in water. Brønsted Acid-surfactant-combined catalyst for ester, ether, thioether, and dithioacetal formation in water

Dehydration reactions in water have been realized by a surfactant-type catalyst, dodecylbenzenesulfonic acid (DBSA). These reactions include dehydrative esterification, etherification, thioetherification, and dithioacetalization. In these reactions, DBSA and substrates form emulsion droplets whose interior is hydrophobic enough to exclude water molecules generated during the reactions. Detailed studies on the esterification revealed that the yields of esters were affected by temperature, amounts of DBSA used, and the substrates. Esters were obtained in high yields for highly hydrophobic substrates. On the basis of the difference in hydrophobicity of the substrates, unique selective esterification and etherification in water were attained. Furthermore, chemospecific, three-component reactions under DBSA-catalyzed conditions were also found to proceed smoothly. This work not only may lead to environmentally benign systems but also will provide a new aspect of organic chemistry in water.

Lewis-acid catalyzed organic reactions in water. The case of AlCl(3), TiCl(4), and SnCl(4) believed to be unusable in aqueous medium

Classical Lewis acids such as AlCl(3), TiCl(4), and SnCl(4), believed to be unusable as catalysts in aqueous medium, efficiently catalyzed regio- and stereoselective azidolysis and iodolysis of alpha,beta-epoxycarboxylic acids in water at pH 4.0 and 1.5, respectively. The concept of water-tolerant metal-salt is reexamined in direct relationship to the aqua ion hydrolysis constant.

[Development of catalytic reactions using water as a solvent]

In recent years, organic reactions in aqueous media have attracted much attention, not only because these reactions eliminate the necessity of vigorous drying of solvents and substrates, but also because unique reactivity and selectivity are often observed in the aqueous reactions. Furthermore, organic reactions in water may lead to the development of environmentally friendly chemical processes. We have now developed various types of catalytic organic reactions in aqueous media. Catalytic asymmetric aldol reactions in aqueous media have attained by using rare earth metal triflates and a chiral multi-dentate ligand. Lewis acid catalysis has become feasible in water by using combinations of water-compatible Lewis acidic cations and anionic surfactants. These new catalysts were found to form stable colloidal dispersions and catalyze various reactions in water. Moreover, Brønsted acid- and palladium-catalyzed reactions in water have also been performed with the aid of surfactants.