Pure Appl. Chem., 2004, Vol. 76, No. 3, pp. 625-633
doi:10.1351/pac200476030625
New insights into the mechanism of molybdenum-catalyzed asymmetric alkylation*
S. W. Krska, D. L. Hughes, R. A. Reamer, D. J. Mathre, M. Palucki, N. Yasuda, Y. Sun, B. M. Trost
Department of Process Research, Merck and Co., Inc., Rahway, NJ 07065, USA; Department of Chemistry, Stanford University, Palo Alto, CA 94305-5080, USA
Abstract:
The major features of the catalytic cycle, including structures of key intermediates, have been determined for the molybdenum-catalyzed asymmetric alkylation. The crystal structure of the π-allyl intermediate exhibits 3-point binding of an anionic ligand. Based on NMR analysis, this species adopts in solution a structure consistent with that observed in the solid state. For the allylic alkylation, the crystal structure predicts the opposite stereochemistry vs. that observed experimentally, which suggests that either the reaction proceeds via a minor isomer (Curtin-Hammett conditions) or with retention of configuration. In addition, CO transfer, promoted by Mo(CO)6, has been found to play a key role in catalyst turnover.