Reductive formylation of amines with CO2 using sodium borohydride: A catalyst-free route

Using sodium borohydride (NaBH4) as the reducing reagent, the reductive fomylation of amines with CO2 was realized at 100 degrees C under catalyst-free conditions, and a series of formylated products were obtained in excellent yields. The reaction mechanism investigation demonstrated that NaBH4 could react with CO2 to form intermediate, which further reacted with amines, producing the formylated compounds. It was indicated that three hydrogen atoms from NaBH4 could involve in the reductive formylation, and therefore only 0.5 equiv. NaBH4 relative to the substrate was enough for getting high product yields. In addition, NaBH4 was also very efficient for the reductive cyclization of o-phenylenediamine with CO2 to synthesize benzimidazoles. NaBH4 as an efficient reducing reagent for the CO2-involed reductive reactions may have promising applications.