Oxidation of 2,5-Dialkylpyrrole Derivatives with Cerium(IV) Ammonium Nitrate

A new Pour-step procedure for the synthesis of 2,5-diformylpyrrole from hexane-2,5-dione was developed. The oxidation reaction of substituted 2,5-dialkylpyrroles with cerium(IV) ammonium nitrate (CAN) has been studied in detail. It was found that the outcome of the reaction strongly depends on the substituents present on the pyrrole moiety and on the reaction conditions. N-Tosyl- and N-mesyl-protected 2,5-dimethylpyrroles and 3,4-diiodo-2,5-dimethylpyrrole were oxidized to the corresponding dialdehydes, whereas 2,5-dialkylpyrroles bearing electron-withdrawing groups at positions 3 and 4 were transformed into the corresponding keto ethers or monoaldehydes rather than into the expected diketones.