oa Editorial [Hot Topic: Water-Mediated Organic Reactions (Guest Editor: Satomi Niwayama)

Recently, development of environmentally friendly reactions has been of central importance in modern synthetic organic chemistry. Water is among the most environmentally friendly and least expensive solvents, and therefore reactions mediated by water should constitute the ideal green chemistry. However, since many organic compounds have limited solubility in water, efficient water-mediated reactions with high selectivities and reactivities are still relatively limited, and hence there is a need for close examination of such research areas. Therefore this mini-thematic/hot topic issue focuses on review articles of recent development of various water-mediated organic reactions. The first review contributed by Vaccaro et al. focuses on the opening of epoxides in aqueous media. Expoxides are known to be among the most reactive and important building blocks in organic synthesis. Ring opening reactions of epoxide are also among the most commonly known reactions that occur in aqueous media under a variety of conditions. This review introduces various stereoselective ring opening reactions of epoxides in water, focusing on desymmetrization and kinetic resolutions, and the role of water is discussed in several examples. The second review contributed by Kobayashi et al. describes various organic reactions in water with chiral Lewis catalysts, such as aldol reactions, hydroxymethylation, Mannich-type reactions, ring opening reactions of meso-epoxides, Nazaro-type reactions, Michael reactions and alkyne addition to imines in water. For the purpose of development of efficient organic reactions in aqueous media, the concepts of Lewis Acid-Surfactant-combined catalysts and silica gel-supported Scandium catalysts with ionic liquid are also introduced. The third review contributed by Muzart et al. is an assembly of various metal-catalyzed reactions such as oxidations of allylic carbons, dihydroxylation and hydroxyalkoxylation of C=C bonds, C-C bond formation, and hydrogenation reactions in water and on water. These reactions are performed in an aqueous solution catalyzed by Cu- or Pd-complex with hydrosoluble ligands, with Pd-nanoparticles or without metal-ion catalysts. The effects of water in these reactions are also addressed. These review articles in this issue contain both published work and unpublished work disclosed only in Ph.D. theses. This guest editor hopes that these contributions will help expand the scope of water-mediated organic reactions and hence green reactions.