Photoredox Catalysis for Building C–C Bonds from C(sp²)–H Bonds

Abstract

Transition metal-catalyzed C-H bond functionalizations have been the focus of intensive research over the last decades for the formation of C-C bonds from unfunctionalized arenes, heteroarenes, alkenes. These direct transformations provide new approaches in synthesis with high atom- and step-economy compared to the traditional catalytic cross-coupling reactions. However, such methods still suffer from several limitations including functional group tolerance and the lack of regioselectivity. In addition, they often require harsh reaction conditions and some of them need the use of strong oxidant, in a stoichiometric amount, avoiding these processes to be truly eco-friendly. The use of photoredox catalysis has contributed to a significant expansion of the scope of C(sp)-H bond functionalizations which include the direct arylations, (perfluoro)alkylations, acylations, and even cyanations. Most of these transformations involve the photochemical induced generation of a radical followed by its regioselective addition to arenes, heteroarenes, or alkenes, leading to the building of a new C(sp)-C bond. The use of photoredox catalysis plays crucial roles in these reactions promoting electron transfer, enabling the generation of radical species and single electron either oxidation or reduction. Such reactions operating at room temperature allow the building of C-C bonds with high chemo-, regio-, or stereoselectivity. This review surveys the formation of C(sp)-C bonds initiated by photoredox catalysis which involves a C(sp)-H bond functionalization step, describes the advantages compared to traditional C(sp)-H bond functionalizations, and presents mechanistic insights into the role played by the photoredox catalysts.

Alkyl Carbon–Carbon Bond Formation by Nickel/Photoredox Cross‐Coupling

“…Owing to the sheer volume of recent literature on transition metal/photoredox dual catalysis and the existence of several relevant reviews, [9,15] we have chosen to focus the scope of this Minireview on photoredox reactions that use C(sp 3 )r adicals to forge carbon-carbon bonds through aN icatalyzed cross-coupling cycle.P hotoredox reactions that accomplish carbon-heteroatom coupling or that employ other metals are therefore excluded. Processes that form carbon-carbon bonds through non-metal catalyzed photoredox mechanisms such as the Giese addition, [16] protoncoupled electron transfer (PCET), [17] radical/polar crossover processes, [18] the Minisci reaction, [19] or cycloadditions, [20] although useful in their own right, are also not discussed.…”

Enhancing Ru(II)‐Catalysis with Visible‐Light‐Mediated Dye‐Sensitized TiO2 Photocatalysis for Oxidative C−H Olefination of Arene Carboxylic Acids at Room Temperature

“…Transition‐metal catalyzed direct C−H bond functionalization reactions have reigned supreme as a sustainable complementary approach to conventional synthetic processes due to their step‐ and atom‐economy . However, in most of the cases, stoichiometric amounts of sacrificial oxidants are necessary for manipulating the oxidation‐state of the active transition‐metal catalyst to enable the crucial redox events in the catalytic cycle –. Recently, visible‐light photo‐redox catalysis has emerged as an alternative catalytic mode of redox manipulation and the groups of Sanford, Rueping, and others have showcased its utility as catalytic internal as well as terminal oxidants in C−H bond activation reactions .…”

Optimizing parameters of tuned mass damper subjected to critical earthquake

“…Furthermore, in this study, the stroke of the passive TMD system ( v s ) is computed using the following relation: where x d and x n are the displacements of the TMD and the roof, respectively, as shown in Figure .…”