Functionalization of C-H Bonds by Photoredox Catalysis

Abstract

Visible-light photoredox catalysis has been successfully used in the functionalization of inert C-H bonds including C(sp )-H bonds of arenes and C(sp )-H bonds of aliphatic compounds over the past decade. These transformations are typically promoted by the process of single-electron-transfer (SET) between substrates and photo-excited photocatalyst upon visible light irradiation (household bulbs or LEDs). Compared with other synthetic strategies, such as the transition-metal catalysis and traditional radical reactions, visible-light photoredox approach has distinct advantages in terms of operational simplicity and practicability. Versatile direct functionalization of inert C(sp )-H and C(sp )-H bonds including alkylation, trifluoromethylation, arylation and amidation, has been achieved using this practical strategy.

Photoredox‐Initiated 1,2‐Difunctionalization of Alkenes with N‐Chloro S‐Fluoroalkyl Sulfoximines

“…Based on previous reports,, two plausible mechanisms could be evoked for this transformation as displayed in Scheme . First, the photoexcitation of the photocatalyst would promote the photoreduction of the sulfoximine 1 by SET reduction, that would give rise to the formation of the sulfoximidoyl radical I .…”

Visible Light Induced Rhodium(I)‐Catalyzed C−H Borylation

“…[5] In spite of this success,t here is still an eed for the development of C À H transformations that can efficiently operate under mild reaction conditions with broad functional-group tolerance and high selectivity.T he recent enthusiasm for visible light driven reactions has resulted in ar ise in the number of innovative catalytic systems that enable CÀHtransformations under mild reaction conditions. [6] Most of these methodologies involve the photosensitization of ap hotoredox catalyst (PC) that promotes the transformation either by hydrogen-atom transfer (HAT) or single-electron transfer (SET; Figure 1a). [7] More recently,bymerging photoredox catalysis and TM catalysis,t his dual catalysis strategy has allowed the installation of unique functional groups with efficient selectivity control (Figure 1b).…”

Functionalization of C(sp2)–H Bonds of Arenes and Heteroarenes Assisted by Photoredox Catalysts for the C–C Bond Formation

“…Since the pioneer works by Gafney and Adamson, who showed that singleelectron-transfer (SET) event can be initiated by the triplet charge-transfer excited state of [Ru(bpy) 3 ] 2+ , [16] the application of polypyridine-metal complexes with metal-ligand charge transfer (MLCT) properties in catalysis has become a useful alternative approach to create new C-C bonds, [17][18][19][20][21][22][23][24][25][26] and more recently to functionalize C-H bonds. [27][28][29][30] The first photoredox functionalization of C(sp 2 )-H bond was reported in 1984 by Deronzier with the [Ru(bpy) 3 ] 2+ -assisted the cyclization of stilbenediazonium salts. [31] Photoredox catalysts (PC n ), such as tris (2,2′-bipyridine) ruthenium (II) [Ru(bpy) 3…”