Supramolecular catalysis of sigmatropic rearrangements: Rate acceleration through encapsulation

ORGN 749

Dorothea Fiedler1, Achim Zahl2, Rudi van Eldik, vaneldik@chemie.uni-erlangen.de2, Robert G. Bergman, bergman@cchem.berkeley.edu3, and Kenneth N. Raymond3. (1) Department of Chemistry, University of California, San Francisco, San Francisco, CA 94143, (2) Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstr. 1, Erlangen, 91058, Germany, (3) Chemical Sciences Division (LBNL) and Department of Chemistry (UCB), Lawrence Berkeley National Laboratory and University of California, Berkeley, Berkeley, CA 94720
Supramolecular container molecules can provide a unique environment for chemical transformations of their guests. We have explored reaction chemistry inside the hydrophobic and chiral cavity of a [Ga4L6]12- tetrahedral assembly and discovered that the cationic 3-aza-Cope rearrangement of enammonium cations is accelerated by encapsulation. A variety of substrates are encapsulated and rearrange within the cavity. Compared to the unencapsulated reaction, rearrangement of the assembly-bound substrates is accelerated by up to three orders of magnitude. Activation Parameters and pressure dependences support the mechanism and catalytic cycle proposed below. The supramolecular host behaves as a catalyst; the reaction cycle turns over in the presence of excess substrate. The substrate scope has been extended to the aza-Cope rearrangement of propargyl-vinyl and allenyl-vinyl ammonium cations. In addition, the [2,3]-Stevens rearrangement of nitrogen ylids has been investigated.

 

Asymmetric Reactions, Molecular Recognition, Self Assembly, Bioorganic Chemistry, Process R&D
8:00 PM-10:00 PM, Wednesday, 16 March 2005 Convention Center -- Hall D, Poster

Division of Organic Chemistry

The 229th ACS National Meeting, in San Diego, CA, March 13-17, 2005