Palladium‐Catalyzed Dehydrogenation of Benzyl Alcohols for Construction of 2‐Arylbenzimidazoles “On Water”

Abstract

An “on water” synthetic strategy for the selective construction of 2‐arylbenzimidazoles involving the dehydrogenation of benzyl alcohols by a π‐benzylpalladium(II) system has been developed. This simple oxidant‐ and base‐free protocol can be achieved under mild conditions in an atom‐economic process from o‐phenylenediamines and benzyl alcohols, affording the desired products in moderate to excellent yields. Notably, the “on water” protocol is essential for achieving this new synthetic method in our catalytic system.

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

“…Very recently, Isao et al. reported a one‐pot method for the selective construction of 1,2‐diphenyl‐1 H ‐benzo[ d ] imidazoles involving the dehydro‐genation of benzyl alcohols by a π‐benzylpalladium(II) system (Scheme c) . The construction of C−C, C−N, C−O, C−S bonds as well as heterocycles has been carried out under oxidative conditions in the Deng group.…”

“…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).…”

“…Benzimidazole is one of the oldest known nitrogen heterocycles and was first synthesized by Hoebrecker and later by Ladenberg and Wundt during 1872-1878. [1] In nature, N-ribosyl dimethylbenzimidazole serves as an axial ligand for cobalt ions in vitamin B 12 . [2] Over years of active research, benzimidazole has evolved as an important heterocyclic system due to its presence in a wide range of bioactive compounds, such as antiparasitics, analgesics, antihypertensives, antivirals and anticancers.…”

“…[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.…”

Ultrafine Pt nanoparticles supported on a dendrimer containing thiol groups: an efficient catalyst for the synthesis of benzimidazoles and benzothiazoles from benzyl alcohol derivatives in water

“…In this step, water accelerates the conversion to C through 5-exo-tet cyclization via a tetrahedral intermediate (Baldwins rules). 38,39 In the last step, the Fig. 7 Purposed mechanism for synthesis of benzimidazole and benzothiazole in the presence of Pt nanoparticle as catalyst (X ¼ NH, S).…”