ECHET96 Search CD [Molecules: None] [Related articles/posters: 036 117 006 004 035 ]

K. N. Houk,* Nicholas C. DeMello, Kevin Condroski, Jens Fennen and Takashi Kasuga

Department of Chemistry and Biochemistry, University of California, Los Angeles CA 90095-1569, USA

Quantum mechanical and force field modelling leads to a new theory for the origin of stereoselection in Jacobsen epoxidations. Ab initio DFT calculations predict a triplet ground state for simple analogues of manganese oxo compounds which are intermediates in the Jacobsen oxidation. Examination of several approaches of olefins to the oxo derivative of Jacobsen's catalyst by empirical force field modelling show that there is a preferred direction of approach of alkene to the oxygen. Semi-empirical PM3(tm) methods accurately reproduce DFT and crystal structure data. Analysis of steric issues involved in the approach of the olefin with either of two enantiotopic faces towards the catalyst results in an explanation for the cause of stereoselectivity in Jacobsen type epoxidation reactions.

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