Remarkable enhancement of reactivity by Brønsted acids in aldol reactions mediated by Lewis acid-surfactant-combined catalysts 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.

Dramatic micellar rate enhancement of the Cu(2+) catalyzed vinologous Friedel-Crafts alkylation in water

A dramatic rate enhancement of the Cu(2+) catalyzed Friedel-Crafts alkylation in water was achieved in the presence of sodium dodecyl sulfate (SDS) micelles.

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.

Highly Diastereoselective Mannich-Type Reactions of Chiral N-Acylhydrazones

The Lewis acid-mediated addition of silyl enolates to easily accessible homochiral N-acylhydrazones derived from 3-amino-2-oxazolidinones proceeded in yields up to 71% and diastereomeric ratios of 99:1. In most cases, optimal reaction conditions entailed the simple use of ZnCl(2) in acetonitrile at room temperature. Hydrazones derived from phenyl-, isopropyl-, and benzyl-substituted 2-oxazolidinones were examined in the reaction in terms of yield and diastereoselectivity. The facile SmI(2)-mediated N-N bond cleavage of the formed hydrazines was demonstrated yielding a beta-amino acid derivative. Hence, the overall reaction sequence constitutes an efficient asymmetric Mannich-type reaction. The sense of diastereoselectivity was explained by a preferential attack on the less shielded Si face of the chiral hydrazones and confirmed by means of X-ray crystallography.

Addition of water to zinc triflate promotes a novel reaction: stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes

A novel stereoselective Mannich-type reaction of chiral aldimines with 2-silyloxybutadienes in the presence of zinc triflate and water has been achieved. The diastereoselectivities of the products were 74-90% de, and no cycloadducts were detected. Classical Mannich-type products were also obtained by using zinc triflate and water with high diastereoselectivities.

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.