Sequential Metal‐Catalyzed N‐Heteroarylation and C–C Cross‐Coupling Reactions: An Expedient Route to Tris(hetero)aryl Systems

Abstract

This paper describes copper‐catalyzed N–C heteroarylation of benzimidazole, 1‐methylbenzimidazolone, imidazole and pyrrole. The products of these reactions then undergo palladium‐catalyzed C–C cross‐couplings with aryl or heteroarylboronic acids under Suzuki–Miyaura conditions to provide a rapid entry, from readily‐available reagents, into tris(hetero)aryl scaffolds comprising two or three N‐heterocyclic rings. The sequential N–C and C–C couplings can be performed in a one‐pot process (two examples are given: >50 % overall yields). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Bifunctional Salen-Cu(II) complex as efficient catalyst for N-arylation of imidazoles and Suzuki-Miyaura coupling reactions

“…Rh-, Ru-and Pd-based noble metal complexes with a large number of phosphorous [3,4] , carbene [5][6][7] , oxime [8,9] , imine [10][11][12] and other ligands [13,14] have been reported as catalysts for such couplings. From an academic, industrial, and economic standpoint, the abundant and inexpensive use of copper has led to remarkable progress in the development of copper-catalyzed C-C and C-N bond formation reactions [15][16][17][18][19] . Buchwald et al [20] and Taillefer et al [21][22][23] revealed rate accelerations when arylations were conducted in the presence of certain copper ligands.…”

Pd-Catalyzed Efficient One-Pot Sequential Cross-Coupling Reactions of Aryl Dihalides

“…Unsymmetric terphenyls and disubstituted pyridines have been prepared through double Suzuki−Miyaura reactions by using different arylboronic acids . Very recently, the sequential copper-mediated C−N and subsequent Pd-catalyzed C−C couplings of aryl dihalides were also known to give tris(hetero)aryl compounds . To achieve high regioselectivity, double couplings of the dihaloarene equivalents have been explored.…”

“…Such a route has been applied for the synthesis of liquid crystal materials via sequencial Negishi/Still couplings . However, some reported sequential coupling reactions suffer disadvantages such as requirement of two different catalysts, the intermediate products have to be separated prior to the second coupling, or using not easily available substrates. ,, From the viewpoint of efficiency, one-pot sequential reactions of commercially available inexpensive aryl dihalides with a single catalyst are desirable, and so far only a few successful examples have been reported. ,, …”

“…were also known to give tris(hetero)aryl compounds. 4 To achieve high regioselectivity, double couplings of the dihaloarene equivalents have been explored. For example, unsymmetrical terphenyls can be obtained through separate Pd-and Ni-catalyzed coupling reactions of bromobenzenesulfonates with arylboronic acids and arylmagnesium bromides 5 and one-pot double coupling of bromoarenediazonium tetrafluoroborate.…”