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.