ASYMMETRIC MICHAEL ADDITIONS CATALYZED BY NI(II) AND CO(II) COMPLEXES WITH HOMOCHIRAL LIGANDS

Two Michael-type addition reactions, of nitromethane to chalcone, reaction (1a), and of methyl 1-oxo-2-indanecarboxylate to methyl vinyl ketone (reaction (1b)) have been tested for catalytic asymmetric induction when carried out in the presence of Ni(II) or Co(II) and homochiral ligands. Proline-derived ligands in conjunction with Ni(II) are found to be moderately effective asymmetric inductors in the former addition (up to 59% e.e.). For this addition, the absolute configuration of the adduct (2) has been established via correlation with (S)-(+)-1-(dimethylamino)-2,4-diphenylbutan-4-one (21). For reaction (lb), Co(II) complexes appear to be the more effective catalysts; the highest e.e. (38%) was obtained with a tetradentate ligand, a diaminodiol (16). Although the e.e.s so far obtained are not much better than those previously obtained, the method appears to allow further improvement.