MN(III)-MEDIATED ELECTROCHEMICAL OXIDATIVE FREE-RADICAL CYCLIZATIONS

Mn(III)-Based oxidative free-radical cyclizations and additions are versatile reactions that have been extensively developed over the past decade allowing free-radical cyclizations to be carried out without toxic tin reagents. Their applicability in large scale synthesis is limited by the requirement for greater than or equal to 2 equivalents of Mn(OAc)(3) per mole of substrate oxidized. While manganese is not expensive, it is toxic, and the disposal of large quantities poses a pollution problem. A variety of procedures were investigated to develop a cheap and safe method for reoxidizing Mn(II) to Mn(III) during the oxidation of the organic substrate. Successful results in some cases were obtained using anodic oxidation to reoxidize Mn(II) to Mn(III) in a mixed solvent of AcOH and EtOH containing NaOAc as an electrolyte. Sodium periodate in DMSO is also capable of reoxidizing Mn(II) to Mn(III).