Tandem electrooxidation - reductive amination of biobased isohexides towards bicyclic diamines.

Isohexide-derived diamines are considered preferred precursors for the production of biobased polyurethanes and polyamides. However, current synthesis methods from isohexides suffer from serious issues concerning selectivity and the recyclability of the process auxiliaries (e.g. homogeneous catalysts), which renders a translation to the industry highly unlikely. Here, we report on the production of such diamine building blocks, via a tandem electrooxidation - reductive amination process in which the process auxiliaries can be easily recycled. The application of (immobilized) TEMPO in combination with simple halides (e.g. NaBr) in the electrochemical step even enables the oxidation of the sterically hindered exo-OHs of the isohexides to the corresponding diketones (yield up to 99%). In the subsequent reductive amination, the produced ketones are atom-efficiently converted to isohexide diamines utilizing NH3, H2, and Ru/C and an acid resin cocatalyst.