Enantioselective 1,3-dipolar cycloadditions of azlactones and electrophilic alkenes catalyzed by dimeric BinapAuTFA complexes

Glycine-derived azlactones react with maleimides using (S)- or (R)-dimeric BinapAuTFA complexes affording the corresponding cycloadducts in good yields and high enantioselections (up to 99% ee). The intermediate carboxylic acids are treated with trimethylsilyldiazomethane and isolated as Δ¹-pyrroline methyl esters. These cycloadducts are transformed into exo-proline derivatives by reduction with NaBH3CN in acidic media. On the other hand, N-benzoylalanine-derived oxazolone reacts with tert-butyl acrylate providing the cycloadduct with the ester group at the 3-position with a trans-relative configuration with respect to the methyl ester group.

This work has been supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) [Consolider INGENIO 2010 CSD2007-00006, CTQ2007-62771/BQU, CTQ2010-20387, FEDER, Generalitat Valenciana (PROMETEO/2009/039)], and by the University of Alicante. M.M.-R. also thanks MICINN for a grant.