Manganese(II)/(III) glycolates: preparation, X-ray crystallographic study,and application in radical cycloaddition reactions

Alternative methods for stereoselective synthesis of the chiral racemic man ganese(II) glycolate have been developed. Its geometry is proven to be inde pendent of the nature of the starting material (Mn(Gly)(3) and Mn(OAc)(3)) and reaction conditions (temperature, solvent). The single-crystal X-ray an alysis shows that a chiral environment around the manganese atom is created by glycolate units lying in the perpendicular planes and water molecules d isposed cis to each other. By its thermodynamic stability, the isolated com plex ranks as second most unstable among five alternative isomeric structur es. Manganese(III) glycolate has been suggested as a novel mediator for rad ical cycloadditions of beta -dicarbonyl compounds to alkenes. It is the fir st time that an alpha -hydroxycarboxylic acid is used as a spectator ligand thus providing a possibility for using this class of compounds in asymmetr ic manganese(III)-mediated radical processes. (C) 2000 Elsevier Science S.A . All rights reserved.