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• 16889-72-8 tert-butyl 2-methylpropanoate 
• 1073-06-9 3-fluorobromobenzene 

Relevant academic research and scientific papers

Rhodium(I)-Catalyzed Tertiary Phosphine Directed C?H Arylation: Rapid Construction of Ligand Libraries

Modification of commercially available monophosphine ligands with either aryl bromides or chlorides by rhodium(I)-catalyzed, tertiary phosphine directed C?H activation is described. A series of ligand libraries containing mono- and diaryl-substituted groups, having different steric and electronic properties, were obtained in high yields. Based on the outstanding properties of their parent scaffolds, the modified ligands have been found to be powerful in organic reactions.

Comparative structural analysis of biarylphosphine ligands in arylpalladium bromide and malonate complexes

The substitution of biarylphosphine ligands was shown to have a marked impact on the α/β selectivity of the arylation of ester enolates. To get further insight into this effect, the solid-state structures of arylpalladium bromide and malonate complexes with four different biarylphosphine ligands were obtained by X-ray diffraction analysis. Structural differences were not very pronounced except for the conformationally restricted CPhos ligand, which showed a bidentate coordination mode in the oxidative addition complex, whereas the other ligands form dimeric species.

On the mechanism of the palladium-catalyzed β-arylation of ester enolates

The palladium-catalyzed β-arylation of ester enolates with aryl bromides was studied both experimentally and computationally. First, the effect of the ligand on the selectivity of the α/β-arylation reactions of ortho- and meta-fluorobromobenzene was described. Selective β-arylation was observed for the reaction of o-fluorobromobenzene with a range of biarylphosphine ligands, whereas α-arylation was predominantly observed with m-fluorobromobenzene for all ligands except DavePhos, which gave an approximate 1:1 mixture of α-/β-arylated products. Next, the effect of the substitution pattern of the aryl bromide reactant was studied with DavePhos as the ligand. We showed that electronic factors played a major role in the α/β-arylation selectivity, with electron-withdrawing substituents favoring β-arylation. Kinetic and deuterium-labeling experiments suggested that the rate-limiting step of β-arylation with DavePhos as the ligand was the palladium-enolate-to-homoenolate isomerization, which occurs by a β-H-elimination, olefin-rotation, and olefin-insertion sequence. A dimeric oxidative-addition complex, which was shown to be catalytically competent, was isolated and structurally characterized. A common mechanism for α- and β-arylation was described by DFT calculations. With DavePhos as the ligand, the pathway leading to β-arylation was kinetically favored over the pathway leading to α-arylation, with the palladium-enolate-to-homoenolate isomerization being the rate-limiting step of the β-arylation pathway and the transition state for olefin insertion its highest point. The nature of the rate-limiting step changed with PCy3 and PtBu3 ligands, and with the latter, α-arylation became kinetically favored. The trend in selectivity observed experimentally with differently substituted aryl bromides agreed well with that observed from the calculations. The presence of electron-withdrawing groups on these bromides mainly affected the α-arylation pathway by disfavoring C-C reductive elimination. The higher activity of the ligands of the biaryldialkylphosphine ligands compared to their corresponding trialkylphosphines could be attributed to stabilizing interactions between the biaryl backbone of the ligands and the metal center, thereby preventing deactivation of the β-arylation pathway.

Palladium-catalyzed β arylation of carboxylic esters

Alter ego: In the presence of an appropriate palladium(0) catalyst, carboxylic esters underwent β arylation instead of the more common α-arylation reaction with aryl halides containing an ortho electronegative substituent (see scheme; Cy = cyclohexyl). An asymmetric version of the reaction gave the product with an enantiomeric ratio of up to 77:23.