Synthesis of amine derivatives from furoin and furil over a Ru/Al2O3 catalyst

Abstract

The direct/reductive amination of carbohydrate-based furoin and furil with NH₃/H₂ was investigated to access amine derivatives. In the sole presence of NH₃, cyclic amines, i.e. 2,3,5,6-tetra(furan-2-yl)pyrazine and 2,2′-bipyridine-3,3′-diol, were generated as the main products from furoin and furil, respectively. Over Ru/Al₂O₃ under NH₃/H₂, 2-amino-1,2-di(furan-2-yl)ethan-1-ol (i.e. alcohol–amine) was generated as the main product with 47% yield at 140 °C for 2 h starting from furoin. The catalyst could be recycled for at least three consecutive runs. An alcohol–imine was the main intermediate that underwent tautomerization to alcohol–enamine/keto–amine leading to cyclic by-products by self-condensation. DFT calculations, complementing the experimental observations, provided detailed molecular-level insight into the reactivity of the alcohol–imine intermediate. Its preferential adsorption on Ru centers via the NH group, with the OH group pointing away from the surface, was found to direct its hydrogenation towards the alcohol–amine as main product. By combining Ru/Al₂O₃ and a silica-anchored N-heterocyclic carbene (NHC) catalyst, the alcohol-amine could be accessed with 42% overall yield in a single reactor.