Dual catalyst systems: Using ureas to provide site-isolation and rate enhancement in asymmetric reactions

ORGN 15

Sarah L. Poe1, Muris Kobaslija, mk346@cornell.edu1, and D. Tyler McQuade, mcquade@chem.fsu.edu2. (1) Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853, (2) Department of Chemistry and Biochemistry, Florida State University, Dittmer Building, Tallahassee, FL 32306
By encapsulating a nitroalkene-forming polymeric amine catalyst within a polyurea shell, we were able to use it in the presence of an enantioselective nickel-based Michael addition catalyst in order to form a product that could not be obtained if the catalysts were not site-isolated or if the steps were performed sequentially rather than in tandem. Kinetic data shows that the polyurea shell of the first catalyst not only provides efficient site-isolation, but it also enhances the rate of the second reaction. A small molecule analog of the microcapsule wall was developed. This urea provides rate enhancement of the Michael addition as well, allowing for reduced loadings of the metal catalyst while maintaining high ee's. Kinetic data suggests the formation of a nickel-urea complex that catalyzes the reaction faster than the nickel catalyst alone. We are currently exploring other asymmetric reactions for which this small molecule urea provides rate enhancement.
 

Asymmetric Reactions and Syntheses
8:00 AM-12:00 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. R06, Oral

Division of Organic Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008