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.
*Plenary and invited lectures presented at the 12th
International Symposium on Organometallic Chemistry Directed Towards
Organic Synthesis (OMCOS-12), Toronto, Ontario, Canada, 6-10 July 2003.
Other lectures are published in this issue, pp.
453-695.
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