Synthesis of 1,5-Diaminonaphthalene Via Electrochemical C,H-Amination of Naphthalene

Since their invention in 1937, polyurethanes (PUR) have found numerous applications in our daily life. [1] A key building block for high performance polyurethanes (Vulkollan®) is 1,5-naphthalene diisocyanate, made from 1,5-diamino naphthalene. The latter is currently made by a rather laborious multistep process. Therefore, a direct and sustainable access to 1,5-naphthalene diisocyanate or the precursor diamine would be of interest. In 2013 Yoshida et al. reported a promising process for the electrochemical C,H amination of electron-rich arenes. [2,3] Through anodic pyridination at a carbon felt anode (graphite) N -arylpyridinium ions are obtained. Aminolysis with piperidine yields the corresponding primary amines. Overoxidation and the introduction of a second amino moiety are suppressed because of the positive charge of the pyridinium intermediates. We successfully demonstrated the twofold, electrochemical C,H amination of naphthalene by employing boron-doped diamond anodes. This innovative electrode material shows a higher performance at more positive potentials. [4] The second amino functionality is, due to electrostatics, regioselectively introduced at position 5. Upon work-up 1,5-diaminonaphthalene and 1-aminonaphthalene are obtained. Currently, the reaction is optimized regarding e.g. current density and electrolyte. It is envisioned, that the positive charge of 1-pyridiniumnaphthalene can be effectively shielded through an appropriate choice of supporting electrolyte (-concentration). Thus, the second oxidation should be facilitated. Furthermore, the scope of the reaction is expanded to other polycyclic aromatic hydrocarbons, as well as other nitrogen-based nucleophiles. References: [1] a) O. Bayer, W. Siefken, H. Rinke, L. Orthner, H. Schild (IG Farben), DRP 728981, 1937 ; b) H.W. Engels, H. G. Pirkl, R. Albers, R. W. Albach, J. Krause, A. Hoffmann, H. Casselmann, J. Dormish, Angew. Chem. Int. Ed. 2013 ; 52 , 9422–9441, Angew . Chem . 2013 , 125 , 9596–9616. [2] T. Morofuji, A. Shimizu, J. I. Yoshida, J. Am. Chem. Soc . 2013 , 135 , 5000–5003 [3] S. R. Waldvogel, S. Möhle, Angew. Chem. Int. Ed. 2015 , 54 , 6398–6399; Angew . Chem . 2015 , 127 , 6496–6497. [4] B. Elsler, D. Schollmeyer, K. M. Dyballa, R. Franke, S. R. Waldvogel, Angew. Chem. Int. Ed . 2014 , 53 , 5210─5213; Angew. Chem. 2014 , 126 , 5311─5314. Figure 1