Abstract
During our studies of manganese(III)-based oxidative free-radical cyclizations1 11"10 we observed to our surprise that
the /3-hydroxy radical 2, prepared by oxidation of the ßketo ester 1 with manganese triacetate in acetic acid, was oxidized by manganese(III) to epoxide 3 in 30-50% yield.7 There are isolated reports that transition-metal oxidants will convert /3-hydroxy radicals to epoxides. Copper(II) has been shown to oxidize /3-hydroxy radicals to epoxides with a second order rate constant of «107 M"1 S"1.11-13 Corey found that oxidative decarboxylation of a /3-hydroxy acid with lead tetraacetate gave a compound tentatively
identified as an epoxide.14,15 Oxidation of /3-hydroxy radicals has also been implicated in the biosynthesis of epoxides from alkenes. We report here studies on the generality, mechanism, and stereochemistry of epoxide formation from /3-hydroxy radicals generated by the decarboxylation of /3-hydroxy acids with lead tetraacetate.