The construction of carbon-heteroatom bonds is one of the most active areas of research in organic chemistry because the function of organic molecules is often derived from the presence of heteroatoms. Although considerable advances have recently been achieved in radical-involved catalytic asymmetric C-N bond formation, there has been little progress in the corresponding C-O bond-forming processes. Here, we describe a photoinduced copper-catalyzed cross-coupling of readily available oxime esters and 1,3-dienes to generate diversely substituted allylic esters with high regio- and enantioselectivity (>75 examples; up to 95% ee). The reaction proceeds at room temperature under excitation by purple light-emitting diodes (LEDs) and features the use of a single, earth-abundant copper-based chiral catalyst as both the photoredox catalyst for radical generation and the source of asymmetric induction in C-O coupling. Combined experimental and density functional theory (DFT) computational studies suggest the formation of π-allylcopper complexes from redox-active oxime esters as bifunctional reagents and 1,3-dienes through a radical-polar crossover process.

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Photoinduced Copper-Catalyzed Asymmetric C-O Cross-Coupling.

Kharasch-Sosnovsky reaction is one of the most powerful methods for allylic oxidation of alkenes. However, the inherent radical mechanism and use of peroxides as both oxidants and oxygen nucleophiles render dearth of universal catalytic systems for highly enantioselective variants and limited scope. Herein, an alternative to the asymmetric Kharasch-Sosnovsky reaction that utilized a chiral copper catalyst and purple-LED irradiation to enable the three-component coupling of 1,3-dienes, oxime esters, and carboxylic acids is reported. This protocol features mild conditions, remarkable scope and functional group tolerance as evidenced by >80 examples and utility in the late-stage modification of pharmaceuticals and natural products. Detailed mechanistic studies provide evidences for the radical-based reaction pathway.

Photoinduced Copper-Catalyzed Asymmetric Three-Component Coupling of 1,3-Dienes: An Alternative to Kharasch–Sosnovsky Reaction

Transition metal-catalysed asymmetric coupling has been established as a robust tool for constructing complex organic molecules. Although this area has been extensively studied, the development of efficient protocols to construct stereogenic centres with excellent regio- and enantioselectivities is highly desirable and remains challenging. Asymmetric transition metal catalysis with light intervention provides a practical alternative strategy to current methods and considerably expands the synthetic utility as a result of abundant feedstocks and mild conditions. This tutorial review comprehensively summarizes the recent advances in transition-metal-catalysed asymmetric coupling reactions with light intervention; in particular, a concise analysis of substrate scope and the mechanistic scenarios governing stereocontrol is discussed.

Recent advances in transition-metal-catalysed asymmetric coupling reactions with light intervention.

Metallaphotoredox catalysis for multicomponent coupling reactions

1,4-Alkylcarbonylation of 1,3-Enynes to Access Tetra-Substituted Allenyl Ketones via an NHC-Catalyzed Radical Relay

1,3-Dienes are readily available feedstocks that are widely used in the laboratory and industry. However, the potential of converting 1,3-dienes into value-added products, especially chiral products, has not yet been fully exploited. By synergetic photoredox/copper catalysis, we achieve the first visible-light-induced, enantioselective carbocyanation of 1,3-dienes by using carboxylic acid derivatives and trimethylsilyl cyanide. Under mild and neutral conditions, a diverse range of chiral allyl cyanides are produced in generally good efficiency and with high enantioselectivity from bench-stable and user-safe chemicals. Moreover, preliminary results also confirm that this success can be expanded to 1,3-enynes and the four-component carbonylative carbocyanation of 1,3-dienes and 1,3-enynes.

Enantioselective Radical Carbocyanation of 1,3-Dienes via Photocatalytic Generation of Allylcopper Complexes

Assemble of Ti3C2 MXene into ZnIn2S4-NiSe2 S-Scheme Heterojunction with multiple charge transfer channels for Accelerated Photocatalytic H2 Generation

g‐C3N4 (g‐CN) with edge grafting of 4‐(1H‐imidazol‐2‐yl) benzoic acid (IBA) and NiS cocatalysts is fabricated via a one‐pot chemical condensation of monomers with urea and subsequent photodeposition. The successful copolymerization of the IBA in g‐CN (g‐CN/IBA) is easily identified by 13C NMR spectra, Fourier transformed infrared spectra, and UV–vis absorption spectra. As a result, the acquired copolymer composites exhibit greatly enhanced visible‐light photocatalytic performance for H2 evolution, in comparison with the undoped g‐CN. The g‐CN‐IBA photocatalyst with the optimal loading amounts of NiS displays an outstanding hydrogen‐evolution rate of 2948.52 µmol g‐1 h‐1 under visible light (λ > 420 nm). The maximum apparent quantum efficiency of g‐CN/IBA‐3%NiS is 3.20% at 450 nm. The enhanced activity can be attributed to the synergism of edge grafting of 4‐(1H‐Imidazol‐2‐yl) benzoic acid and loading of NiS cocatalysts, which not only shows a remarkable redshift of the optical‐absorption compared to g‐CN, effectively improving the absorption in the visible range, but also effectively avoids recombination and drives the favorable separation of photogenerated carriers in plane. This work provides a protocol for simultaneously increasing the active sites of light absorption and surface reactions of g‐CN‐based photocatalysts to maximize photocatalytic hydrogen production activity.

Photodeposition of NiS Cocatalysts on g‐C3N4 with Edge Grafting of 4‐(1H‐Imidazol‐2‐yl) Benzoic Acid for Highly Elevated Photocatalytic H2 Evolution

2D/2D covalent organic framework/CdS Z-scheme heterojunction for enhanced photocatalytic H2 evolution: Insights into interfacial charge transfer mechanism

Selective activation and transformation of C-O bonds under mild conditons is of great significance in synthetic chemistry because of the widespread existence of carbon-oxygen single bond. In this work, allenyl...

Jun-Chuan Bai

Papers

Enantioselective Radical Carbocyanation of 1,3-Dienes via Photocatalytic Generation of Allylcopper Complexes

Assemble of Ti3C2 MXene into ZnIn2S4-NiSe2 S-Scheme Heterojunction with multiple charge transfer channels for Accelerated Photocatalytic H2 Generation

Photodeposition of NiS Cocatalysts on g‐C3N4 with Edge Grafting of 4‐(1H‐Imidazol‐2‐yl) Benzoic Acid for Highly Elevated Photocatalytic H2 Evolution

2D/2D covalent organic framework/CdS Z-scheme heterojunction for enhanced photocatalytic H2 evolution: Insights into interfacial charge transfer mechanism

Photoinduced C-O bond cleavage for copper-catalyzed allenyl radical cyanation