Visible-light-mediated borylation of aryl and alkyl halides with a palladium complex

A toolbox approach to revealing a series of naphthocarbazoles to showcase photocatalytic reductive syntheses

The development of highly reducing photocatalysts to functionalize arenes via the generation of reactive aryl radicals under mild and environmentally benign reaction conditions has emerged as a noteworthy approach in the realm of organic synthesis. Herein, we report a readily synthesized series of novel naphthocarbazole derivatives (NCs) as organo-photocatalysts, which, upon irradiation under 390 nm light, acquire high reducing power to catalyze several reductive transformations. The promising properties revealed by in depth photophysical and electrochemical studies ( = -1.9 V to -2.07 V vs. SCE, τ = 5.59 to 7.12 ns) demonstrate NCs to be versatile catalysts, and notably, rational variation of the substituents (NC1-NC6) modulates their success as efficient photoreductants. Detailed DFT calculations of the frontier MO diagrams and energy levels revealed them to be non-donor-acceptor type molecular scaffolds. The applicability of the NCs as catalysts was demonstrated in reductive dehalogenative borylation, phosphorylation, and dehydrohalide intramolecular C-C coupling reactions, as well as the dimerization of carbonyls and imines. Visible-light-irradiated selective reductive desulfonylation from heteroaromatics and peptides further enhances their synthetic utility.

1,4-Aminoarylation of Butadienes via Photoinduced Palladium Catalysis

A visible-light-induced, three-component palladium-catalyzed 1,4-aminoarylation of butadienes with readily available aryl halides and aliphatic amines has been developed, affording allylamines with excellent E-selectivity. The reaction exhibits exceptional control over chemo-, regio-, and stereoselectivity, a broad substrate scope, and high functional group compatibility, as demonstrated by the late-stage functionalization of bioactive molecules. Mechanistic investigations are consistent with a photoinduced radical Pd(0)-Pd(I)-Pd(II)-Pd(0) Heck-Tsuji-Trost allylation cascade.

Recent Expedition in Pd- and Rh-Catalyzed C(Ar) -B Bond Formations and Their Applications in Modern Organic Syntheses

Transition metal-catalyzed borylation has emerged as a powerful and versatile strategy for synthesizing organoboron compounds. These compounds have found widespread applications in various aspects, including organic synthesis, materials science, and medicinal chemistry. This review provides a concise summary of the recent advances in palladium- and rhodium-catalyzed borylation from 2013 to 2023. The review covers the representative examples of catalysts, substrates scope and reaction conditions, with particular emphasis on the development of catalyst systems, such as phosphine ligands, NHC-carbene, and more. The diverse array of borylative products obtained for further applications in Suzuki-Miyaura coupling, and other transformations, are also discussed. Future directions in this rapidly evolving field, with the goal of designing more efficient, selective borylation methodologies are highlighted, too.

Visible Light-Induced Transition Metal Catalysis

In recent years, visible light-induced transition metal catalysis has emerged as a new paradigm in organic photocatalysis, which has led to the discovery of unprecedented transformations as well as the improvement of known reactions. In this subfield of photocatalysis, a transition metal complex serves a double duty by harvesting photon energy and then enabling bond forming/breaking events mostly via a single catalytic cycle, thus contrasting the established dual photocatalysis in which an exogenous photosensitizer is employed. In addition, this approach often synergistically combines catalyst-substrate interaction with photoinduced process, a feature that is uncommon in conventional photoredox chemistry. This Review describes the early development and recent advances of this emerging field.

One-pot synthesis of Ag-Cu-Cu2O/C nanocomposites derived from a metal-organic framework as a photocatalyst for borylation of aryl halide

Mixed metal-metal oxide/C (Ag-Cu-Cu2O/C) nanocomposites were synthesized by the heat treatment of a metal-organic framework under a N2 flow using the one-pot synthesis method. The as-prepared nanocomposites were characterized using a range of techniques, such as TEM, elemental mapping, XRD, N2 sorption, UV-Vis DRS, and XPS. The nanoparticles were successfully formed with high dispersion in porous carbon materials and high crystallinity based on the analysis results. The Ag-Cu-Cu2O/C nanocomposites (35 nm) showed high photocatalytic activity and good recyclability toward the borylation of aryl halides under a xenon arc lamp. This result can enhance the interest in photocatalysis for various applications, particularly in organic reactions, using a simple and efficient synthesis method.

Photoinduced Borylation for the Synthesis of Organoboron Compounds

Organoboron compounds have important synthetic value and can be applied in numerous transformations. The development of practical and convenient ways to synthesize boronate esters has thus attracted significant interest. Photoinduced borylations originated from stoichiometric reactions of alkanes and arenes with well-defined metal-boryl complexes. Now, photoredox-initiated borylations, catalyzed by either transition metal or organic photocatalysts, and photochemical borylations with high efficiency have become a burgeoning area of research. In this Focus Review, we summarize research on photoinduced borylations, especially emphasizing recent developments and trends. This includes the photoinduced borylation of arenes, alkanes, aryl/alkyl halides, activated carboxylic acids, amines, alcohols, and so on based on transition metal catalysis, metal-free organocatalysis, and direct photochemical activation. We focus on reaction mechanisms involving single-electron transfer, triplet-energy transfer, and other radical processes.

Light-induced borylation: developments and mechanistic insights

Organoboron compounds are very important derivatives because of their profound impacts on medicinal, biological as well as industrial applications. The development of several novel borylation methodologies has achieved momentous interest among synthetic chemists. In this scenario, eco-friendly light-induced borylation is progressively becoming one of the best synthetic tools in recent days to prepare organoboronic ester and acid derivatives based on green chemistry rules. In this article, we have discussed all the UV- and visible-light-induced borylation strategies developed in the last decade. Furthermore, special attention is given to the mechanisms of these borylation methodologies for better understanding of reaction insights.

Construction of polysubstituted spiro[2.3] or [3.3] cyclic frameworks fused with a tosylated pyrrolidine promoted by visible-light-induced photosensitization

A novel visible-light-induced intramolecular [2 + 2] cycloaddition of methylenecyclopropanes (MCPs) for the rapid construction of polysubstituted spiro[2.3] or [3.3] cyclic frameworks fused with a tosylated pyrrolidine.

Corannulene-based nanographene containing helical motifs

The synthesis and structural analyses of corannulene-PAH hybrids 1 with a [4] helicene subunit and 2 with a [7] helicene subunit have been reported.

Visible-Light-Induced Ni-Catalyzed Radical Borylation of Chloroarenes

A highly selective and general photoinduced C-Cl borylation protocol that employs [Ni(IMes)₂] (IMes = 1,3-dimesitylimidazoline-2-ylidene) for the radical borylation of chloroarenes is reported. This photoinduced system operates with visible light (400 nm) and achieves borylation of a wide range of chloroarenes with B₂pin₂ at room temperature in excellent yields and with high selectivity, thereby demonstrating its broad utility and functional group tolerance. Mechanistic investigations suggest that the borylation reactions proceed via a radical process. EPR studies demonstrate that [Ni(IMes)₂] undergoes very fast chlorine atom abstraction from aryl chlorides to give [Ni^I(IMes)₂Cl] and aryl radicals. Control experiments indicate that light promotes the reaction of [Ni^I(IMes)₂Cl] with aryl chlorides generating additional aryl radicals and [Ni^II(IMes)₂Cl₂]. The aryl radicals react with an anionic sp²-sp³ diborane [B₂pin₂(OMe)]^- formed from B₂pin₂ and KOMe to yield the corresponding borylation product and the [Bpin(OMe)]^•- radical anion, which reduces [Ni^II(IMes)₂Cl₂] under irradiation to regenerate [Ni^I(IMes)₂Cl] and [Ni(IMes)₂] for the next catalytic cycle.