The Synthesis of Trans-enediones from Furan Derivatives using Pyridinium Chlorochromate: An Explanation

The reaction of pyridinium chlorochromate (PCC) with furan derivatives gives the corresponding enediones. However, the reaction of pyridinium chlorochromate with furan to give enedione derivatives cannot be performed by using commercial PCC. XRD and XPS analysis of the reagents coupled with DFT calculations can allow us to explain this different behavior. Homemade and commercial PCC have different colors and show some differences in the XRD spectrum. XPS shows the presence of a relevant amount of Cr(III) in the homemade reagent. DFT calculations demonstrate that Cr(III) impurities in the reagent could catalyze the reaction with furan derivatives if an oxygen atom in the Cr(III) derivative attacks the furan ring while it is reoxidized by PCC through the migration of a chlorine atom.