Formation of quaternary stereocenters by copper-catalyzed Michael reactions with L-valine amides as auxiliaries.
Extensive investigations of chiral auxiliaries and active metals for Michael addition of 1,3-dicarbonyl compounds with vinyl ketones are summarized. Our efforts result in a widely applicable auxiliary-mediated, copper(II) acetate-catalyzed procedure. For these purposes, L-valine diethylamide is an optimal chiral auxiliary giving quaternary stereocenters with up to 99 % ee at ambient temperature. No inert or anhydrous conditions are required, the solvent is simply acetone, and the auxiliary can be recovered almost quantitatively after workup.
Christoffers
Jens
J
Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany. jchr@po.uni-stuttgart.de