A Bimetallic Palladium(II) Catalyzed Synthesis of 1,2-Dibromo Compounds

A bimetallic palladium(II) catalyst containing a triketone ligand and a bridging dinitrogen ligand oxidizes aromatic and cyclic aliphatic olefins in bromide-containing aqueous-THF to 1,2-dibromo compounds and bromohydrins. With aromatic olefins, the 1,2-dibromo products were obtained in a 70–80% yield and the bromohydrins in a 10–15% yield; this observation is opposition to that obtained in chloride containing medium where the chlorohydrin product predominates. The oxidation of 2,3-dihydrofuran gave trans-2,3-dibromotetrahydrofuran, 3-oxotetrahydrofuran, and 3-bromo-2- hydroxytetrahydrofuran in relative yields of 75%, 15%, and 10%, respectively. On the other hand, the oxidation of cyclopentene and cyclohexene affords only trans-1,2- dibromo products in about 90% yield. The stereochemistry is consistent with an anti-attack of bromide followed by decomposition involving attack of bromide from the coordination sphere of the Pd(II). The procedure outlin