Can CO2 Be a Catalyst? Yes, CO2-catalyzed N-formylation of Aliphatic Amines with DMF

Carbon dioxide (CO2) was found to serve as a novel and green catalyst for the first time in N-formylation of amines with N, N-dimethylformamide (DMF), wherein only the aliphatic amines were applicable to afford the formamides in the yield of 71-95%. The isotope labeling experiment with DMF-d7 indicated that the N-formyl group in the formylated product was originated from DMF rather than CO2. The control experiments and the in situ high-pressure FT-IR spectra demonstrated that the formation of the carbamate salt of cyclohexylammonium cyclohexylcarbamate (A) derived from the reaction of CO2 with cyclohexylamine was the driving force for this reaction. Accordingly, the mechanism of CO2-catalyed N-formylation of aliphatic amines with DMF was proposed, involving the formation of carbamate salt intermediate with enhanced nucleophilicity in anion in favor of the attack on carbonyl-group of DMF.