Mechanism of Manganese(III)-Based Oxidation of β-Keto Esters

Article abstract of DOI:10.1021/jo00245a001

The rate-determining step in the oxidation of 2-substituted acetoacetate esters such as 10b by Mn(OAc)3*2H2O is the loss of a proton from the 10b-Mn(III) complex 17b to form 18b.The rate-determining step in the oxidation of 2-unsubstituted acetoacetate esters such as 10a by Mn(OAc)3*2H2O in the presence of an alkene is the oxidation of Mn(III)-10a-alkene complex 20a to give the addition product 21a.In the absence of alkene, a much slower electron transfer from the enolate to the oxo-centered metal system to give 19a is the rate-determining step.Oxidative cyclization of 1b produces oxocyclopentanecarboxylates such as 4b in poor yield since overoxidation of the product occurs at a rate comparable to that of the initial cyclization.Oxidative cyclization of 1a produces oxocyclohexanecarboxylates such as 4a in good yield since the oxidation of 1a is much faster than the oxidation of 1b.Overoxidation can be prevented by oxidative cyclization of 2-chloroacetoacetates such as 30a and 36a followed by zinc reduction to give 32c and 39c in good overall yield.