Catalytic dehydrogenation chloranil

Aromatizations play a particularly prominent role in the synthesis of carbazoles since both the Fischer cyclization (Borsche s method) of cyclohexanones (Section 3.06.3.4.2) and the cycloaddition of 2-vinylindole (Section 3.06.6.1) yield tetrahydrocarbazoles. Both catalytic dehydrogenation over palladium/carbon catalyst and dehydrogenation with chloranil have been employed to effect aromatization (80JA4772,79JOC4402). 

High-potential quinones, such as DDQ and chloranil, are important stoichiometric reagents in organic synthesis with notable applications in the oxidative functionalization of activated C-H bonds and dehydrogenation to form (hetero)arenes [1]. These reactions can be rendered catalytic in quinone by using certain transition metal salts, anodic oxidation, or molecular oxygen to regenerate the quinone in situ. 

Alternative cocatalysts, such as [Fe(pc)]20 (pc = phthalocyanine) and AIBN, have also been reported for catalytic aerobic DDQ oxidation reactions, though these have seen less widespread application than NO [28]. Aerobic quinone-catalyzed dehydrogenation reactions using less oxidizing quinones, such as chloranil, have been reported using polymer-incarcerated noble metal catalysts reported by Kobayashi and colleagues [29, 30]. 

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