MN(III)-MEDIATED TANDEM OXIDATIVE CYCLIZATIONS OF BETA-DIESTERS - INFLUENCE OF CU(II) UPON THE CHEMOSELECTIVITY OF THE REACTION

Mn(III)-mediated oxidative cyclization of esters derived from allylmalonic and benzylmalonic acids afforded through two consecutive cyclizations bislactones (17, 5) and bicyclic lactones (19, 21) or tricyclic lactones (7, 9). The ratio of these products is controlled by the stereoselectivity of the first step involving the intramolecular addition of a carbon-centered radical to a double bond. Oxidations conducted either in the presence of stoichiometric cupric ion or without added Cu(II) provide a comprehensive view of the respective influences of Mn(III) and Cu(II) upon the chemoselectivity of the reaction, which are related to their ability to oxidize radicals of different classes. For example, the primary and secondary radicals 3a and 3b, which are not efficiently oxidized by Mn(III), undergo cyclization leading to the trans fused tricyclic gamma-lactones 9a and 9b exclusively in the absence of cupric ion.