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Density Functional Theory Determination of an Axial Gateway To Explain the Rate and Endo Selectivity Enhancement of Diels−Alder Reactions by Bis(oxazoline)-Cu(II)
journal contribution
posted on 2004-05-19, 00:00 authored by Jason DeChancie, Orlando Acevedo, Jeffrey D. EvanseckA novel conceptual model and unique understanding of rate and endo selectivity enhancements
delivered by bis(oxazoline)-Cu(II) Lewis acid catalysts in the Diels−Alder reaction of cyclopentadiene and
acrylate imide is presented. Despite previously reported kinetic and spectroscopic studies, the physical
reasons for endo selectivity and rate enhancements remain poorly understood. Large-scale density functional
calculations using Becke three-parameter density functional theory with the nonlocal correlation of Lee,
Yang, and Parr and the 6-31G(d) basis set have been carried out for the first time to understand the
geometric and energetic consequences of C2-substituent variation. The unique positioning of the tert-butyl
C2-substituent with respect to the diene, referred to as the “axial gateway”, maintains the electrophilicity of
the catalyst by shielding the reactive metal center from nucleophilic attack. The interplay between steric
and electronic factors is crucial to understanding the observed enhanced rates and endo selectivity.