Water as solvent in organic synthesis

Organic reactions using water as solvent are reviewed with a focus on peric yclic reactions, carbonyl additions, stoichiometric organometallic reaction s, oxidations and reductions which show an unusual outcome in terms of reac tivity and selectivity compared with those performed in organic solvent. Th e advantages of using water as a solvent are discussed and related to the h ydrophobic effects and the hydrogen-bonding ability of water with a special emphasis on its very high cohesive energy density which strongly favors or ganic reactions having a negative activation volume.