Origins of Stereoselectivity in the Corey-Chaykovsky Reaction. Insights from Quantum Chemistry.

Reaction pathways of the Corey-Chaykovsky epoxidation reaction have been compared quantum chemically. Of the concerted, torsional rotation and anti addition pathways the latter two were found to be favored both in the gas phase and in CH(2)Cl(2) in a model system. Several theoretically previously uncharacterized stationary points were located, and selective solvent effects were observed. On the anti addition pathway the C-C bond formation transition state A, suitably substituted to allow comparison with published experimental data, was able to predict both the absolute stereochemistry of the main product and, qualitatively, the distribution of its other stereoisomers. The quantum chemical protocol reported here is useful in designing new sulfides for the Corey-Chaykovsky reaction.