The reaction of variously substituted enamides with Mn(OAc)3 dihydrate afforded β-lactamic products in modest to good yields. The success of the reaction depended mostly on the solvent and reaction conditions. The substitution pattern of the enamidic double bond was found to be of primary importance for the outcome and mechanism of the reaction. The formation of azetidin-2-ones was stereoselective, affording lactams with a trans relationship between the substituents at C-3 and C-4. The reaction proved to be diastereoselective when enamides bearing a chiral group on the nitrogen atom were used.
The Mn(III)-based procedure was carried out either in a purely oxidative way, or in a mixed oxidative- fragmentative pathway. In the latter case, only azetidin-2-ones vinylated at C-4 were obtained. In special cases the obtained β-lactams were overoxidizable affording tricyclic products through an aromatic radical substitution.
Buy this Article