Dirhodium(II)-Catalyzed Carbonylation Peroxidation of α,β-Unsaturated Esters: Mechanistic Insight into the Role of Aryl Aldehydes

Article abstract of DOI:10.1021/acs.inorgchem.7b00888

Peroxidation has received considerable attention as a synthetically useful method used to prepare organic peroxides, which are useful synthetic building blocks in synthetic chemistry. The difunctionalization of alkenes to introduce a peroxide and another functional group has become a useful tool for quickly increasing molecular complexity in synthesis. In this work, a three-component oxidative coupling of aryl aldehydes with α,β-unsaturated esters and tert-butyl hydroperoxide catalyzed by dirhodium(II) catalyst Rh₂(esp)₂ (esp = α,α,α′,α′-tetramethyl-1,3-benzenedipropanoate) under mild conditions is developed. The synthesized carbonylation peroxidation products (β-peroxyketones) are stable enough to be isolated by silica gel column and characterized. The β-peroxyketones used as reactants have been applied to the synthesis of the epoxides, polysubstituted furans, carbazole alkaloids, and biologically important natural products. Interestingly, besides being a reactant, aryl aldehydes also play an important role in avoiding the catalyst deactivation during the reaction as shown by ultraviolet/visible analysis. The excess amount of aldehydes was used to ensure the stability of the Rh₂(esp)₂ catalyst in the reaction by forming the monoaldehyde ligated dirhodium(II) complex. It is important to note that the aldehydes were also found to reduce the inactive Rh₂(esp)₂Cl species generated in the reaction.