A molecular mechanics study of copper(II)-catalyzed asymmetric Diels-Alder reactions

A simple molecular mechanics force field for the study of complexes important in the bis-(oxazoline) copper(II)-catalyzed Diels-Alder reaction of cyclopentadiene with acrylimide dienophiles has been developed. The parameter set has been based on the MMFF94 force field as implemented in the Molecular Operating Environment (MOE) and supplemented by available experimental and DFT calculated data. Control over the electronic preference for a square-planar complex geometry has been achieved by introducing a dummy bond. Catalyst-substrate complexes and approximate transition states have been studied by stochastic conformational searches to investigate conformational preferences and to estimate regio- and enantioselectivities based on the steric characteristics of different bis(oxazoline) ligands. While prediction of regioselectivity is reliable, factors determining enantioselectivity are more subtle, and predictions have been only moderately successful. Further computational experiments have been used to elucidate the source of some of these discrepancies.