Palladium-Catalyzed Direct Arylation of Indoles with Cyclohexanones

Abstract

A novel palladium catalyzed approach to 3-arylindoles was developed from indoles and cyclohexanones. Various cyclohexanones acted as aryl sources via an alkylation and dehydrogenation sequence using molecular oxygen as the hydrogen acceptor. This method showed good regioselectivity and afforded 3-arylindoles as the sole products.

Palladium-Catalyzed Aerobic Dehydrogenation of Cyclic Hydrocarbons for the Synthesis of Substituted Aromatics and Other Unsaturated Products

“…63 The cyclohexene intermediate was independently synthesized and shown to convert into the aryl-substituted indole product. The cyclohexanones represent arene surrogates, similar to the aryl ether and aniline synthetic routes described above.…”

Palladium-catalyzed benzothieno[2,3-b]indole formation via dehydrative–dehydrogenative double C–H sulfuration using sulfur powder, indoles and cyclohexanones

“…45 Treatment of 1-methyl-1H-indole (1a) with 4methylcyclohexanone (2b) in the presence of sulfur powder affords intermediate 1-methyl-3-(4-methylcyclohex-1-en-1-yl)-1H-indole (5a). 21 …”

Transition‐Metal‐Free Synthesis of 1,2‐diphenyl‐1H‐benzo[d] Imidazole Derivatives from N‐phenylbenzimidamides and Cyclohexanones

“…Although there are other methods available for the construction of 1,2diphenyl-1H-benzo[d] imidazoles, the utilization of cheap and non-aromatic coupling partners under transition-metal-free conditions is rare and challenging. [12] The con-struction of CÀ C, [13] CÀ N, [14] CÀ O, [15] CÀ S [16] bonds as well as heterocycles has been carried out under oxidative conditions in the Deng group. [9] In 2011, S. You et al disclosed a palladium-catalysed cascade amination that allows regiospecific and modular synthesis of a library of structurally diverse 1,2-disubstituted (hetero)aryl fused imidazoles (Scheme 1a).…”

“…[11] Very recently, Isao et al reported a one-pot method for the selective construction of 1,2-diphenyl-1H-benzo[d] imidazoles involving the dehydro-genation of benzyl alcohols by a π-benzylpalladium(II) system (Scheme 1c). [12] The con-struction of CÀ C, [13] CÀ N, [14] CÀ O, [15] CÀ S [16] bonds as well as heterocycles has been carried out under oxidative conditions in the Deng group. In these transformations, cyclohexanones were used as a versatile aryl source via a dehydrogenation tautomerization sequence.…”