Aerobic and Efficient Direct Arylation of Five-Membered Heteroarenes and Their Benzocondensed Derivatives with Aryl Bromides by Bulky α-Hydroxyimine Palladium Complexes

Abstract

In the present work, a series of α-hydroxyimine palladium complexes with bulky substituents (i.e., {[Ar-NC(R)− C(R) 2 −OH]PdCl 2 } (C1, R = Me, Ar = 2-diphenylmethyl-4,6-dimethylphenyl; C2, R = Me, Ar = 2,6-bis(diphenylmethyl)-4-methylphenyl; C3, R = Me, Ar = 2,6-bis(diphenylmethyl)-4-methyoxylphenyl; C4, R = Me, Ar = 2,6-bis(diphenylmethyl)-4-chlorophenyl; C5, R = Ph, Ar = 2,6-dimethylphenyl; C6, R = Ph, Ar = 2,6-diisopropylphenyl)) were synthesized and characterized. The structures of palladium complexes C1 and C2 were determined by X-ray diffraction. These bidentate N,O-palladium complexes were applied for direct arylation under aerobic conditions. The effects of the reaction conditions and ligand substitution on the catalytic activity were evaluated. Upon a low palladium loading of 0.5 mol %, the bulky palladium complex C6 was successfully used to catalyze the cross-coupling of a variety of five-membered heteroarenes and their benzo-condensed derivatives with (hetero)aryl bromides. The mechanistic investigation on the direct arylation supported the involvement of a Pd(0)/Pd(II) CMD process.

Ru‐Catalyzed Carbonylative Murai Reaction: Directed C3‐Acylation of Biomass‐Derived 2‐Formyl Heteroaromatics

“…Extension to thiophene 2‐carboxaldehyde was also envisaged, to verify the generality of the heterocyclopentadiene family (Figure e). Although some TM‐catalyzed direct functionalizations of pyrrole or thiophene 2‐carboxaldehydes have been reported, these studies have mainly addressed C5‐arylation and C5‐alkylation, while the C3‐functionalization has been only very marginally explored …”

“…Extension to thiophene 2-carboxaldehyde was also envisaged, to verify the generality of the heterocyclopentadiene family (Figure 1e). Although some TMcatalyzed direct functionalizations of pyrrole or thiophene 2-carboxaldehydes have been reported, these studies have mainly addressed C5-arylation [39][40][41][42] and C5-alkylation, [23] while the C3-functionalization has been only very marginally explored. [24,43] Herein, we disclose the first C3-carbonylative versions of the Murai reaction on furfural derivatives, pyrrole 2-carboxaldehydes and their benzo-fused analogs -indoles -as well as on thiophene 2-carboxaldehydes, through their corresponding aldimines, which act as removable directing groups.…”

Metal-free C–H arylation of imidazoheterocycles with aryl hydrazines

“… 8 Conventionally, arylation of imidazo[1,2- a ]pyridine is carried out by transition-metal-catalyzed cross-coupling reactions using aryl halide/tosylate/mesylate as the aryl source. 9 Despite these advances in the functionalization of this moiety, to the best of our knowledge, there is no metal-free protocol for the arylation of imidazo[1,2- a ]pyridines. This prompted us to develop a transition-metal-free method for the arylation of imidazo[1,2- a ]pyridines.…”

One Pot Selective Arylation of 2-Bromo-5-Chloro Thiophene; Molecular Structure Investigation via Density Functional Theory (DFT), X-ray Analysis, and Their Biological Activities

“…These reactions allow efficient synthesis of mono substituted and di-substituted thiophenes by using K 3 PO 4 as base. However, the compounds 2a – c and 3a – c have already been reported by following different methodologies [ 18 , 19 , 20 , 21 , 22 ], while their biological activities and density functional theory (DFT) studies are being first time reported. After accomplishing the successful synthesis of various mono and di substituted thiopehenes, in continuation of our previous work [ 23 , 24 ], DFT studies were conducted not only to explore the structural properties but also to compare the theoretical structural parameters with those from X-ray diffraction results.…”