Phosphine-Free Palladium-Catalyzed Direct Arylation of Imidazo[1,2-a]pyridines with Aryl Bromides at Low Catalyst Loading

Abstract

Ligand-free Pd(OAc)(2) was found to catalyze very efficiently the direct arylation of imidazo[1,2-a]pyridines at C3 under very low catalyst concentration. The reaction can be performed employing as little as 0.1-0.01 mol % catalyst with electron-deficient and some electron-excessive aryl bromides.

Extending the utility of [Pd(NHC)(cinnamyl)Cl] precatalysts: Direct arylation of heterocycles

“…In our case, comparable yields were obtained when the catalyst loading was decreased from 0.1 to 0.01 mol %, highlighting the high efficiency of the catalytic system (Table 4, entries 14 and 15). Following the same trend as reported by Doucet [45], a better reactivity was observed with bromobenzenes substituted with EWGs compared to with EDGs (Table 4, entries 16 and 17).…”

“…This class of substrate has recently been involved, by Doucet et al [45], in direct arylation with a catalytic charge of Pd(OAc) 2 ranging from 0.1 to 0.01 mol %. In our case, comparable yields were obtained when the catalyst loading was decreased from 0.1 to 0.01 mol %, highlighting the high efficiency of the catalytic system (Table 4, entries 14 and 15).…”

Reactivity of 2,1‐Benzisoxazole in Palladium‐Catalyzed Direct Arylation with Aryl Bromides

“…[9] We have recently reported that the use of the "de Vries conditions" promoted the coupling of aryl bromides with several heteroaromatics. [10] The coupling reactions of 2,1-benzisoxazole and 2-bromonaphthalenew ith 1o r 0.5 mol %P d(OAc) 2 catalysta t1 50 8Ca fforded the target product 1 in very high yields of 78 and 80 %, respectively (Table 1, Entries 2a nd 3). The use of 1mol %P dCl 2 catalystw as less effective, as 1 was isolated in only 35 %y ield (Table 1, Entry 4).…”

Influence of the solvent and of the reaction concentration for palladium-catalysed direct arylation of heteroaromatics with 4-bromoacetophenone

“…We have recently reported that the phosphine-free Pd(OAc) 2 catalyst promotes very efficiently the direct arylation of some heteroaromatics in DMA [18]. We initially employed this phosphine-free procedure in order to determine the influence of the amount and nature of the solvent for Pd-catalysed direct arylations.…”

“…We initially employed this phosphine-free procedure in order to determine the influence of the amount and nature of the solvent for Pd-catalysed direct arylations. A first set of reactions using thiophene 2-carbonitrile (0.75 mmol) and 4-bromoacetophenone (0.5 mmol) as the coupling partners was carried out under previously reported reaction conditions [18], but in 4, 1 or 0.5 mL of solvent with only 0.1 mol% Pd(OAc) 2 catalyst ( Table 1, column 3). In the presence of polar solvents, DMA, NMP and DMF, high conversions of 4-bromoacetophenone and yields of coupling product 1 were obtained ( Table 1, entries 1-3, 5-7 and 9-11 in column 3).…”