Binap-gold(I) trifluoroacetate as a bifunctional catalyst for the synthesis of chiral prolines through 1,3-dipolar cycloaddition of azomethine ylides

Highly enantioselective 1,3-dipolar cycloadditions of amino acid-derived azomethine ylides with alkenes have been performed, for the first time, under gold-catalysis using (Sa)- or (Ra)-Binap-gold(I) trifluoroacetate complexes, with the cationic Binap-gold acting as a Lewis acid and the counteranion as a base. Maleimides and trans-1,2-bis(phenylsulfonyl)ethylene were reacted with imino esters at room temperature in the absence of a base to afford, in very good yields, the corresponding polysubstituted prolines with total endo-diastereoselection and higher enantioselectivities than the Binap-silver trifluoroacetate complex.This work has been supported by the DGES of the Spanish Ministerio de Educación y Ciencia (MEC) (Consolider INGENIO 2010 CSD2007-00006, and CTQ2007-62771/BQU), by the Generalitat Valenciana (PROMETEO/2009/039), and by the University of Alicante. M.M.-R. thanks MEC for a predoctoral fellowship and F.-L. W. thanks the UQ Graduate School for a Research Travel Grant