Catalytic Enantioselective Radical Transformations Enabled by Visible Light

Abstract

Visible light has been recognized as an economical and environmentally benign source of energy that enables chemoselective molecular activation of chemical reactions and hence reveal a new horizon for the design and discovery of novel chemical transformations. On the other hand, asymmetric catalysis represents an economic method to satisfy the increasing need for enantioenriched compounds in the chemical and pharmaceutical industries. Therefore, combining visible light photocatalysis with asymmetric catalysis creates a wider range of opportunities for the development of mechanistically unique reaction schemes. However, there arise two main problems like undesirable photochemical background reactions and difficulties in controlling the stereochemistry with highly reactive photochemical intermediates which can pose a serious challenge to the development of asymmetric visible light photocatalysis. In recent years, several methods have been developed to overcome these challenges. This review summarizes the recent advances in visible light‐induced enantioselective reactions. We divide our discussion into four categories: Asymmetric photoredox organocatalysis, asymmetric transition metal photoredox catalysis, asymmetric photoredox Lewis acid catalysis and asymmetric photoinduced energy transfer catalysis. Special emphasis has been given to different catalytic activation modes that enable the construction of challenging carbon‐carbon and carbon‐heteroatom bond in an enantioselective fashion. A brief analysis of substrate scope and limitation as well as reaction mechanism of these reactions has been included.

Visible Light-Induced Aerobic Oxidative Dehydrogenation of C–N/C–O to C=N/C=O Bonds Using Metal-Free Photocatalysts: Recent Developments

“…Among all the photocatalysts, transition metal-based compounds [11][12][13][14], metal-free molecules [3,[15][16][17][18][19] and semiconductors [20,21] are the most utilized. These promoters have been applied successfully to many photochemical transformations, such as oxidations [22][23][24][25][26], cycloadditions [27][28][29][30], C-H bond functionalizations [31][32][33][34], photoredox reactions [6,16,17,[35][36][37][38][39][40][41][42][43] and even enantioselective reactions [44][45][46][47][48][49][50][51]. In addition, other effective photocatalysts have been widely applied for photocatalysis in energy and environment [52][53]…”

Construction of Chiral Cyclic Compounds Enabled by Enantioselective Photocatalysis

“…This review mainly discusses the research progress of enantioselective photocatalysis for constructing chiral cyclic compounds by photo-induced asymmetric cycloaddition reaction in the past 5 years, though some comprehensive contents regarding this topic were reported by the pioneers [4][5][6][7][8]. This paper is divided into seven parts according to the structural types of rings: the construction of 3-membered rings, 4-membered rings, 5-membered rings, 6-membered rings, 7-membered rings, macroring, and multi-rings.…”

Visible‐Light‐Mediated Ring‐Opening Reactions of Cyclopropanes

“…[56] Other advantages of visible light photoredox catalysis include benign reaction conditions, controlled radical reactions, and it can also be used as a combination with organocatalysis for asymmetric synthesis. [57][58][59][60] Cyclopropane ring-opening reactions under visible light photoredox catalysis opened up a new avenue to achieve a variety of molecules with different functional groups. Different organic and metal-based photocatalysts are used to carry out these challenging transformations (Figure 1).…”