Computational Insights into "Lone Pair-Lone Pair Interaction-Controlled" Isomerization in the Asymmetric Total Syntheses of (+)-3-()-Laureatin and (+)-3-()-Isolaureatin.

Described herein is our computational study to rationalize the stereoselective epimerization of α,α'--disubstituted oxolane and oxetane ketones and to the corresponding α,α'- ketones and reported in our previous total syntheses of (+)-3-()-isolaureatin () and (+)-3-()-laureatin (). Density functional theory (DFT) calculations using appropriately truncated models revealed that the α,α'- ketones are more stable than the α,α'- ketones, in very good agreement with experimental results. The computational results showed that the isomer with a longer interatomic distance between the two ring oxygen atoms was lower in energy, which suggested the presence of repulsive interactions between those oxygen atoms. Support for these distance-dependent repulsive interactions came from the observation that the energy differences between the two isomers correlated with the solvent polarity. Most importantly, a larger interoxygen distance difference could be responsible for the enhanced stereoselectivity for epimerization of oxetane ketone compared to oxolane ketone [0.25 Å ( only) vs 0.13 Å (/ = 4:1)].