AB INITIO-BASED FORCE-FIELD MODELING OF THE TRANSITION-STATES AND STEREOSELECTIVITIES OF LEWIS-ACID CATALYZED ASYMMETRIC DIELS-ALDER REACTIONS

Transition states for the Diels-Alder reactions of butadiene and cyclo pentadiene with methyl acrylate coordinated to BH3 have been located w ith ab initio molecular orbital calculations and the 3-21G basis set; the activation energies were also evaluated by single point calculatio ns with the 6-31G basis set. In addition a solvent cavity (SCRF) calc ulation at the RHF/3-21G level was performed for the reaction of cyclo pentadiene and methyl acrylate coordinated to BH3 in a medium with a d ielectric constant of 9.08. These data have been used to develop a mod ified MM2 force field applicable to the prediction of stereochemistrie s of Lewis acid catalyzed reactions of chiral acrylates to dienes. Thi s force field has been shown to reproduce the selectivities of a numbe r of literature examples. It has also been applied to the predictions of stereoselectivities of new reactions. Insights into the controlling elements in the stereoselectivity are obtained.