Cycloaddition reactions in water

Abstract With the increasing focus on the green chemistry aspects of organic synthesis, the use of water as a reaction medium has greatly been expanded in the last few decades. Water is a highly desirable solvent for chemical reactions in terms of green chemistry principles such as cost, safety, abundance, and environmental concerns. A wide range of reaction types has already been explored using water as the reaction solvent, including those which were considered impossible, such as olefin metathesis, cross-coupling reactions, cycloadditions, Claisen rearrangements, click reactions, oxidations, reductions, Michael reaction, Aldol reaction, Mannich reaction, etc. In this chapter, we focused our discussion on the discovery and development of various cycloaddition reactions employing water as the solvent. We also described various aspects of these reactions like the effect of water medium on rate enhancements, regio- and stereoselectivity through hydrophobic effect, and hydrogen bonding effect. We also included a small discussion about “on water” reactions which conceptually differ from “in water” reactions.