Azobenzene Synthesis from Only Nonaromatic Compounds via Catalytic Dehydrogenative Aromatization

Azobenzenes have been ubiquitously utilized and synthesized in well-established methods represented as azo coupling for a long time; however, all the available azobenzene synthesis strategies use aromatic compounds as substrates, which inherently limit the regioselectivity of substituents because of ortho/meta/para-orientation and frequently require multistep procedures. Dehydrogenative aromatization from cyclohexanones, which can be regioselectively functionalized using classical methods without the aforementioned limitation, has recently attracted attention, but the lack of multifunctional dehydrogenation catalysts for both aromatization and azo bond formation and/or the difficult product selectivity control have hindered its application in azobenzene synthesis. Herein, we report an unprecedented strategy for the synthesis of diverse azobenzenes, including unsymmetrical ones, from only nonaromatic compounds, that is, cyclohexanones and hydrazine, using an Au–Pd alloy nanoparticle catalyst and a suitable hydrogen acceptor (nitrobenzene). Thorough mechanistic studies revealed that the present reaction is enabled by adsorption control and relay catalysis involving concerted dehydrogenation, which are unique features of alloy nanoparticles.