Jeremy Steinbacher - Use of Bifunctional Ureas to Increase the Rate of Proline-Catalyzed α-Aminoxylations

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  Publication Details (including relevant citation   information): Poe, Sarah L., Bogdan, Andrew R., Mason,   Brian P., Steinbacher, Jeremy L., Opalka, Suzanne M., McQuade, D.   Tyler, J. Org. Chem., 2009, 74  (4), pp 1574-1580

  Abstract: The rate of the proline-catalyzed   α-aminoxylation of aldehydes is significantly increased in the   presence of a bifunctional urea. Structure?activity relationship   data indicate that both an amine and a urea are crucial for rate   enhancement. The evidence presented herein suggests that this   rate enhancement originates from the hydrogen bonding interaction   between the bifunctional urea and an oxazolidinone intermediate   to increase the rate of enamine formation. Proline derivatives   that are incapable of forming oxazolidinones exhibit no rate   enhancement in the presence of the bifunctional urea. The rate   enhancement is general for a variety of aldehydes, and the faster   reactions do not reduce yields or selectivities.

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