Ketal Claisen rearrangements of allylic alcohols and simple ketals can proceed through multiple transition states to give different regio- and diastereomers as shown. The partitioning of the reaction through the multiple reaction pathways is subject to the Curtin-Hammett principle, and evaluation of these product mixtures in a theoretical context requires knowledge of the Gibbs energies of the multiple transition states. Density Functional Theory (B3LYP) can be used to evaluate the geometries and free energies of these transition states and predict relative product ratios. These ratios can be compared with experimental results in order to determine how well DFT techniques treat transition states for these systems. We found that in many cases the DFT and experimental results were in reasonable agreement, but a few cases showed large discrepancies. We present the results of Random Phase Approximation and Complete Active Space SCF calculations for these latter systems and discuss possible reasons for the disagreement we observe.

Computational studies on regio- and diastereoselection in ketal Claisen rearrangements

255th National Meeting (2018)

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