EXPERIMENTAL AND THEORETICAL-STUDY OF THE INFLUENCE OF THE SOLVENT ON ASYMMETRIC DIELS-ALDER REACTIONS

Rate, endo/exo and diastereofacial selectivities of the Diels-Alder reaction between cyclopentadiene and (-)-menthyl acrylate were measured in a series of organic solvents and organic-aqueous mixtures. Regression analyses show that a model with the alpha-empirical solvent parameter accounts for most of the changes in rates and diastereofacial selectivities, whereas in the case of the endo/exo selectivity, inclusion of the pi-* and delta parameters is needed. Theoretical calculations carried out on the model reaction between methyl acrylate and cyclopentadiene using dielectric continuum and supermolecule models do not clearly show the effect of the different solvation mechanisms on rate. However, they agree with the above-mentioned influence of alpha and pi-* on the endo/exo and diastereofacial selectivities