Solvent effects on stereoselectivity: more than just an environment

Stereoselectivity is a major topic in organic synthesis. Intensive investigations into the role of solvents on diastereo- and enantioselective reactions, as well as temperature-dependent measurements of diastereomeric and enantiomeric ratios, have shed light on the existence of dynamic solvation effects. In this tutorial review, several examples of non-linear Eyring plots in stereoselective nucleophilic additions, cycloadditions, photochemical and enzymatic reactions are reported. Experimental data and spectroscopic analyses obtained in aliphatic and aromatic hydrocarbons, halohydrocarbons, ethers and mixtures lead to the formulation of a hypothesis on the inversion temperature phenomenon as being due to an equilibrium between distinct solute-solvent clusters, which are the real reactive species in solution.