Copper‐Catalyzed Coupling Reactions of Aryl Halides and Phenols by 4,4’‐Dimethoxy‐2,2’‐bipyridine and 4,7‐Dimethoxy‐1,10‐phenanthroline

Abstract

Several Cu(I) complexes of 2,2'-bipyridines were studied for the catalytic coupling of aryl iodides and phenols and 4,4'dimethoxy-2,2'-bipyridine was shown to be an effective ligand of CuI in 1:2 (CuI:ligand) ratio for the synthesis of a wide range of diaryl ethers (up to 97% yield) using K 3 PO 4 as base in DMF at 100°C. The catalysis was highly dependent on the reaction temperature and was successfully applied in the coupling with more attractive and challenging substrates, aryl bromides, at 140°C in good-to-excellent yields (78À 95%). Moreover, the heteroaromatic effect for the reaction was studied and gave a comparable result with phenyl group (up to 95% yield). Significantly, a structurally related N,N-bidentate ligand, 4,7dimethoxy-1,10-phenanthroline, exhibited better performance for less-reactive combinations of aryl halides and phenols.

Efficient pyrazole moiety-containing ligands for Cu-catalyzed O-arylation of phenols

“…This reveals that the combination of pyrazole and pyridine moieties as a N2-ligand is highly efficient for the O-arylation reaction. Moreover, new N3-ligands L4-L7 afforded yields comparable to that obtained using L8, which were much higher than that using the simple 2,2′-bipyridine [30]. Therefore, the appropriately arranged three pyridine moieties effectively work for the reaction.…”

“…To the best of our knowledge, no study has reported the activities of these seven ligands in O-arylation. In order to investigate the potential of the ligands, the arylation of p-cresol with 4iodotoluene was studied at 100 °C in DMSO in the presence of 10 mol% CuI and 10 mol% ligand, which are 50% and 75% lower than the amounts used for several bipyridine derivatives in our previous work, respectively [30]. The results are summarized in Figure 3.…”

“…In order to understand the characteristics of L1 that make it the best ligand, L8, as the most efficient bipyridine ligand [30], was applied under the same reaction conditions. As shown in Figure 3, L8 gave a 23% lower yield than that of L1 (Table S2, entries 10 vs. 2), although it afforded ~90% yield when four times more of its amount (40 mol%) was used with 20 mol% CuI [30]. This reveals that the combination of pyrazole and pyridine moieties as a N2-ligand is highly efficient for the O-arylation reaction.…”

“…However, some relatively expensive reagents, such as Cu(CH3CN)4BF4 [24], Cu/C [26], and CuI/KF/Al2O3 [27], and moisture-sensitive Cs2CO3 [26,28] are often required for highly efficient O-arylation. In our previous work [30], we comprehensively studied some typical bidentate ligands and found that electron-rich 4,4′-dimethoxy-2,2′bipyridine and 4,7-dimethoxy-1,10-phenanthroline afforded higher yields than those of simple bipyridine and phenanthroline under typical reaction conditions, using CuI and K3PO4 as the catalyst and base, respectively. However, the exploration of new ligands is still necessary to promote the reaction with less amount of a catalyst.…”

“…Herein, we report the application of a series of ligands containing the pyrazole moiety (L1-L3) and their activities in Cu-catalyzed O-arylation, as well as the ligands (L4-L7) featuring only the pyridine moiety ( Figure 1). For comparison, an efficient symmetric N2-ligand, 4,4′-dimethoxy-2,2′-bipyridine (L8) [30], was also investigated in this study. L1 was chosen as an asymmetric N2-ligand having both Npy and Npz atoms and was employed in the preparation of a complex with CuI in acetonitrile.…”