Micellar nanoreactors for organic transformations with a focus on "dehydration" reactions in water: A decade update

Although nature uses the aqueous environment in most of its chemical/biochemical transformations, water as solvent was totally neglected in organic transformations till the end of the last century because of its poor ability to solubilize most of the organic compounds. However, growing environmental concerns make it imperative to replace toxic organic solvents with benign solvents like water. Over the last few decades, the use of catalytic amounts of surfactants in the aqueous media has proved to be the best solution to overcome the problem of insolubility and hydrolytic decomposition of many organic compounds in water. The surfactants form a colloidal, micellar, or other organized phases that serve as "nanoreactors" in aqueous media. The field is called "micellar catalysis" that acts as a greener alternative to conventional organic synthesis. The hydrophobic interior of micelles can successfully accomplish the most challenging task of "dehydration reactions" in water. The last two decades have witnessed enormous contributions of "dehydration reactions" in micellar media. In addition, incredible rate acceleration and selectivities have been observed in micellar media. The technology lends advantages of reusability and easy scalability in the synthetic processes towards setting-up a new dimension of benign chemical transformations. The purpose of the present review to capture the enormous contributions of the last decade on "dehydration reactions" in micellar media including various condensation reactions, formation of acid-derivatives, multicomponent reactions, and the formation of heterocycles to give a comprehensive idea to readers on the development of this field. The review also covers a brief account on micelle-assisted reactions other than dehydrations taking the key and recent contributions of various types of reactions such as cross-coupling reactions, CeH activation, asymmetric catalysis, oxidation-reduction, click chemistry etc. (C) 2021 Elsevier Ltd. All rights reserved.