Autocatalytic Green Synthesis of Imines in Traceless Medium

For the first time, condensations of amines with carbonyl compounds have been performed in supercritical carbon dioxide (sc-CO₂). The reactions with aldehydes or active ketones proceed at moderate temperatures (35–55 °C) without use of external catalysts. The process is autocatalytic: it is accelerated by the carbonic acid generated in situ by interaction between the released water and the CO₂ medium. The imine products were obtained in high yields in a crystalline form and did not require further purification. The one-pot transfer hydrogenation and [4+2] cycloaddition reactions performed in the CO₂ medium have uncovered attractive prospects for facile green synthesis of more complex and valuable compounds from the generated in situ imine products.