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

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.