Cobalt-Catalyzed C–H Acetoxylation of Phenols with Removable Monodentate Directing Groups: Access to Pyrocatechol Derivatives

Abstract

An efficient cobalt-catalyzed C–H acetoxylation of phenols has been developed by using PIDA (phenyliodine diacetate) as a sole acetoxy source to synthesize pyrocatechol derivatives for the first time. The key feature of this method is the use of earth-abundant metal cobalt as the green and inexpensive catalyst for the acetoxylation of C­(sp2)–H bonds under neutral reaction conditions. Furthermore, the gram-scale reaction and late-stage functionalization demonstrated the usefulness of this method.

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

“…Chelated cobalt(II) catalysts, such as [Co(acac) 2 ], can also be used in C-H activation methods to modify 2-phenoxypyridines, from which other biological activities can be discovered. Although they present a lower oxidation state, they are also powerful catalysts, as described by Gou, Cao, and co-workers for a C-H acetoxylation of phenol derivatives (Scheme 43B) [205]. In the presence of phenyliodine(III) diacetate (PIDA) the reaction leads to several ortho-directed acetoxylated products in moderate to good yields (Scheme 41C).…”

“…In this work, a nickel-based metalorganic framework (MOF-74-Ni) mediated a C-H arylation process of several azole derivatives (Scheme 64A). The desired arylated products were obtained in good yields, including compounds known to present important biological activities (Scheme 64B and C) such as the caffeine derivative from 203 [289], texamine (204) [290], balsoxin (205) [290], and the previously mentioned uguenenazole (194) [276].…”

Cobalt‐Catalyzed C(sp2)−O Bond Formation by Directing Group Assisted C−H Activation

“…In 2020, Gou et al reported the first example of cobalt-catalyzed CÀ H acetoxylation of phenol derivatives (Scheme 14). [48] In their study, they used a pyridine directing group, which is easy to remove after targeted functionalization. [49] This cobalt catalysis features greener acetoxylation owing to the combinatorial use of phenyliodine diacetate (PIDA) as a single acetoxy source and oxygen as a non-toxic oxidant.…”

Divergent Regioselective Csp2–H Difluoromethylation of Aromatic Amines Enabled by Nickel Catalysis

“…What’s more, among these numerous elegant procedures reported in the literature, the directing group-free ortho -C–H difluoromethylation of aromatic rings to access difluorooxindoles, which are effectively accomplished by using 3d metal catalysis alone, also remains scarce. Furthermore, although nickel has high catalyst flexibility and chemical versatility for most molecular skeletons, previous attempts at nickel-catalyzed selective C–H difluoromethylation of aromatic rings have consistently failed so far. − Herein, on the basis of our previous understanding of 3d metals, we develop a new and inexpensive catalytic system to vanquish the regioselectivity and sustainability of C–H difluoromethylation of aromatic rings (Figure c).…”