Cobalt(II)-Catalyzed Oxidative C–H Arylation of Indoles and Boronic Acids

Abstract

Co(II)-catalyzed C-H C2 selective arylation of indoles with boronic acids through monodentate chelation assistance has been achieved for the first time. The unique features of this methodology include mild reaction conditions, highly C2 regioselectivity, and employment of a Grignard reagent-free catalytic system. A wide range of substrates, including unreactive arenes, are well tolerated, which enables the construction of the coupling products efficiently. This new strategy provides an alternative and versatile approach to construct biaryls using inexpensive cobalt catalyst.

Cobalt‐Catalyzed Hiyama‐Type C−H Activation with Arylsiloxanes: Versatile Access to Highly ortho‐Decorated Biaryls

“…Despite major progress, stoichiometric amounts of highly reactive Grignard reagents were required, hence significantly comprising the tolerance of synthetically useful functional groups (Scheme a). While subsequent advances were represented by C−H arylations with nucleophilic boronic acids, they called for stoichiometric amounts of cobalt (Scheme b), and/or costly hexafluoroisopropanol (HFIP) as the solvent …”

“…While subsequent advances were represented by CÀHa rylations with nucleophilic boronic acids, [7] they called for stoichiometric amountso fc obalt (Scheme 1b), [7] and/or costlyh exafluoroisopropanol( HFIP) as the solvent. [8] Organosilicon arylating agents are attractive, becauseo f their environmentally benign nature, ease of preparation, robustness, and outstanding stability. [9] Unfortunately,t his unique stabilityd irectly translates into as ignificantlyr educed transmetalation reactivity.N onetheless,t he challenge associated with the use of less reactive silicon-baseda rylating reagents was successfully addressed, albeit with the aid of noble 4d metalc atalysts, such as palladium, [10,11] rhodium, [12] iridium [13] and ruthenium.…”

C−H Functionalization of Indoles by 3d Transition‐Metal Catalysis

“…In 2017, Song and co‐workers reported the cobalt‐catalyzed oxidative C−H arylation of indoles with aryl boronic acids using Mn(OAc) 2 .4H 2 O as an oxidant (Scheme ) . In this reaction, the 2‐pyridinyl or 2‐pyrimidinyl was employed as a directing group for the reaction.…”

“…In 2017, Song and co-workers reported the cobalt-catalyzed oxidative CÀ H arylation of indoles with aryl boronic acids using Mn(OAc) 2 .4H 2 O as an oxidant (Scheme 2). [14] In this reaction, the 2-pyridinyl or 2-pyrimidinyl was employed as a directing group for the reaction. The reaction needed an acidic solvent HFIP, occurred at relatively mild reaction conditions and demonstrated a wide range of substrates.…”

Advance in C-H Arylation of Indoles

“…随后, 施章杰、李焕荣和徐立进等 [76] 在吲哚 N 原子 上引入嘧啶导向基团, 该嘧啶基团可以引导 Rh 催化剂 活化邻位的 C-H 键. 从而使苯甲酸类衍生物通过脱羧 Co 催化下的吲哚 C2 位芳基化亦有被报道, 宋毛平 和牛俊龙等 [83] 通过在吲哚 N 原子上引入嘧啶或者吡啶 基团, 在 Co 催化剂作用下, 以芳基硼酸作为芳基化试 剂高选择性地构建了吲哚 C2 位芳基-芳基 C-C 键(Eq. 52).…”