A new copper acetate-bis(oxazoline)-catalyzed, enantioselective Henry reaction

The nitroaldol (Henry) reaction is an important carbonyl addition process that affords products that may be transformed into valuable building blocks.1 Therefore, it is not surprising that recent efforts have focused on the development of catalytic enantioselective reaction variants. The current contributions to this area have been highlighted by the recent studies of Shibasaki and Trost.2-5 The purpose of this Communication is to report a new catalyst system for the nitroaldol reaction (eqs 1,2; M) Cu, X) OAc). The basis for the current study was to identify a weakly Lewis acidic metal complex bearing moderately basic charged ligands (X) that would facilitate the deprotonation of nitroalkanes (eq 1) as a prelude to the aldol addition process (eq 2). It was felt that divalent metal acetate-ligand complexes of the general structure A might meet these requirements because acetate has been employed as a Brønsted base in the racemic nitroaldol reaction.