How intermediate analysis inspires selectivity control for the catalytic reductive amination of carbohydrates toward ethylene polyamines

The synthesis of bio-based amines via the catalytic reductive amination of carbohydrate-derived substrates has gained growing interest over the past few years. However, research has mainly been directed to ethanolamine formation, while industrially relevant ethylene polyamines have received less attention. Here, we report the selective synthesis of such polyamines via the catalytic reductive amination of sugar-derived glycolaldehyde (GA) with diamine reagents. In an attempt to achieve high polyamine yields, three disruptive bottom-up strategies are proposed. Firstly, using a diol solvent, such as ethylene glycol, enhances the dehydration rate and favorably affects the chemical equilibrium. Secondly, the formation of several by-products is circumvented by separating the amination from the hydrogenation step, following a one-pot-two-step procedure. Thirdly, carboxylic acids, such as oxalic acid, catalyze the keto-enol tautomerization reaction prior to polyamine formation. Integrating these strategies in one general procedure yields unique ethylene polyamines from GA and various diamine reagents, exceeding 80C% product yield.