Origins of stereoselectivity in the Corey-Chaykovsky reaction. Insights from quantum chemistry

Reaction pathways of the Corey-Chaykovsky epoxidation reaction have been co mpared quantum chemically. Of the concerted, torsional rotation and anti ad dition pathways the latter two were found to be favored both in the gas pha se and in CH2Cl2 in a model system. Several theoretically previously unchar acterized stationary points were located, and selective solvent effects wer e observed. On the anti addition pathway the C-C bond formation transition state A, suitably substituted to allow comparison with published experiment al data, was able to predict both the absolute stereochemistry of the main product and, qualitatively, the distribution of its other stereoisomers. Th e quantum chemical protocol reported here is useful in designing new sulfid es for the Corey-Chaykovsky reaction.