Aerobic epoxidation via alkyl-2-oxocyclopentanecarboxylate co-oxidation with cobalt or manganese Jacobsen-type catalysts

In the presence of methyl, tert-butyl, or (-)-menthyl esters of 2-oxocyclopentanecarboxylic acids Jacbosen-type complexes of cobalt(II) and manganese(III) form active catalysts for alkene epoxidation using molecular oxygen. Alkyl-1-hydroxy-2-oxocyclopentanecarboxylates and 1-alkyl-2-oxo-hexanedicarboxylic acids are formed as co-oxidation products. The (-)-menthyl/cobalt system is selective for epoxide production but the products are racemic consistent with radical epoxidation in solution rather than at the cobalt complex. The manganese Jacobsen-type complex gives lower yields of epoxides (40-60%) but for 2,2-dimethylchromene and styrene these are optically active (12-60% ee).