Cobalt‐Catalyzed Annulation Reactions via C−H Bond Activation

Abstract

Considerable research attention has been directed towards the use of first‐row transition metals in organic synthesis. The more abundant, and less expensive cobalt is considered to be an effective alternative for expensive second and third‐row noble metals, especially in C−H bond functionalization reactions. In this Minireview, we will summarize the features, and recent achievements of the Co‐catalyzed directing group assisted C−H activation/cyclization reactions and their mechanistic insights.

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…There is no such thing as a single dominant metal species, but Pd, 48 , 49 Rh, 50 , 51 and Ru 52 – 54 share together the top spot. Moreover, increasing examples using Ni, 55 – 58 Co, 55 , 59 – 64 Ir, 64 – 66 Cu, 67 – 69 Fe, 3 , 55 , 63 , 70 , 71 and Mn 72 – 74 are appearing in the literature.…”

Palladium‐Catalyzed Benzofulvenation of o‐Arylanilines through C−H Bond Activation by Using Two Diarylacetylenes as an Implicit Benzofulvene

“…developed the first efficient method of metal‐catalyzed alkylation by using ketone as the directing group (DG) through C−H bond activation, transition‐metal‐catalyzed C−H bond activation has emerged as a powerful tool for selective C−H functionalization . Transition metals, such as rhodium, iridium, cobalt, and palladium, have been used to catalyze cycloaddition of acetylenes with 2‐alkenyl anilines, phenols, N ‐substituted anilines, and aryl iodides, respectively, mainly yielding substituted indolines, chromenones, and an extended aromatic π‐system. Furthermore, iminoquinone, carbonyl, sulfonyl, alkyl, and aryl‐masked amino groups have been identified as favorable groups for directing C−H bond cleavage at the ortho or 2′‐position of o ‐phenylanilines and enabling transition‐metal‐catalyzed insertion of activated olefins, diaryliodonium salts, CO, fullerene, or intramolecular cyclization to yield phenanthridines, substituted triphenylenes, phenanthridinones, fullerobenzoazepines, and carbazoles, respectively.…”

HFIP‐Assisted C−H Functionalization by Cp*CoIII: Access to Key Reactive Cobaltacycles and Implication in Catalysis

“…Based on the mechanistic proposals found in the literature, at the beginning both reactions share identical reactive intermediates, as is depicted in Scheme . However, the two pathways differ in the steps that follow the migratory insertion: protodemetalation in the presence of a protic source versus reductive elimination/reoxidation sequence . Therefore, the comparison of the HFIP effect on these two reactivity patterns represents a particular interesting case, since a priori, the fluorinated alcohol could affect them differently.…”