Arylation of indoles using cyclohexanones dually-catalyzed by niobic acid and palladium-on-carbons
Kazuho Ban1, Yuta Yamamoto, Hironao Sajiki
1Laboratory of Organic Chemistry, Gifu Pharmaceutical University, 1-25-4 Daigakunishi, Gifu 501-1196, Japan. sajiki@gifu-pu.ac.jp sawama@gifu-pu.ac.jp.
Abstract:
3-Arylindoles were easily constructed from indoles and cyclohexanone derivatives using a combination of catalytic niobic acid-on-carbon (Nb2O5/C) and palladium-on-carbon (Pd/C) under heating conditions without any oxidants. The Lewis acidic Nb2O5/C promoted the nucleophilic addition of indoles to the cyclohexanones, and the subsequent dehydration and Pd/C-catalyzed dehydrogenation produced the 3-arylindoles. The additive 2,3-dimethyl-1,3-butadiene worked as a hydrogen acceptor to facilitate the dehydrogenation step.
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