Terminal C(sp3)-H borylation through intermolecular radical sampling

Cuprate ion-pair catalyzed conjugate borylation of vinyl sulfones in a biphasic system

Herein we report the conjugate borylation of vinyl sulfones mediated by ion pairing, which enables the efficient synthesis of β-sulfonyl alcohols bearing diverse functionalities in 13-98% yields. Further mechanistic investigations suggest the formation of anionic boryl-copper intermediates that kinetically accelerate reactant transfer across phases and provide enhanced boryl nucleophilicity.

Selective Degradation of Polyethylene Terephthalate Plastic Waste Using Iron Salt Photocatalysts

Plastic pollution poses a significant challenge to environmental conservation. Efficient recycling of plastic is a key strategy to address this issue. Polyethylene terephthalate (PET), commonly found in plastic bottles, represents a substantial portion of plastic waste. Consequently, the efficient degradation and recycling of PET is crucial for the sustainable development of society. However, the implementation of methods for PET depolymerization and recycling typically necessitates alkaline/acidic pre-treatment and significant energy input for heating. Here, we propose a gentle, and highly efficient photocatalysis approach for selectively degrading PET plastic waste into terephthalic acid (TPA) in high yield (up to 99 %) using cost-effective iron salts. Notably, this method achieved excellent selectivity with high TON and TOF values, applying oxygen or air as environmentally friendly oxidants. In addition, the solvent can be recycled without compromising the TPA yield, and large-scale reactions can be performed smoothly.

One-Pot Decarbonylative Borylation of Aliphatic Aldehydes

We present a mild and direct method for the radical borylation of simple aliphatic aldehydes. By employing an enamine and a photocatalyst under light irradiation, aldehydes can be transformed effectively into alkyl boronic esters via a formal decarbonylative process. This alternative route for radical borylation synthesis can not only be applied to the transformation of primary, secondary, and tertiary aldehydes but also be adapted to other radical conversion reactions through the generated alkyl radical intermediate. Mechanistic studies indicate that 4-alkyl-1,4-dihydropyridines, formed in situ from the aldehyde and enamine, are the key intermediate for the borylation process.

Metal-Free Electrochemical C─H Chlorination of Terminal Alkanes

Although research on the activation of C─H bonds in alkanes has been ongoing for decades, there are still few strategies that are both highly selective and suitable for industrial production. Herein, we report a highly selective method for the chlorination of terminal C─H bonds in alkanes by combining electrochemistry and organocatalysis. The specific cavity size of organic molecular catalysts ensures high regioselectivity, while the use of inexpensive and readily reusable graphite felt electrodes, a simple electrochemical device, and mild conditions enables the reaction to maintain good efficiency even when applied to kilogram-scale production.

Unified approaches in transition metal catalyzed C(sp3)-H functionalization: recent advances and mechanistic aspects

In organic synthesis, C(sp3)-H functionalization is a revolutionary method that allows direct alteration of unactivated C-H bonds. It can obviate the need for pre-functionalization and provides access to streamlined and atom economical routes for the synthesis of complex molecules starting from simple starting materials. Many strategies have evolved, such as photoredox catalysis, organocatalysis, non-directed C-H activation, transiently directed C-H activation, and native functionality directed C-H activation. Together these advances have reinforced the importance of C(sp3)-H functionalization in synthetic chemistry. C(sp3)-H functionalization has direct applications in pharmacology, agrochemicals, and materials science, demonstrating its ability to transform synthetic approaches by creating new retrosynthetic disconnections and boost the efficiency of chemical processes. This review aims to provide an overview of current state of C(sp3)-H functionalization, focusing more on recent breakthroughs and associated mechanistic insights.

Iron-Catalyzed Aerobic Carbonylation of Methane via Ligand-to-Metal Charge Transfer Excitation

The integration of ligand-to-metal charge transfer (LMCT) catalytic paradigms with radical intermediates has transformed the selective functionalization of inert C-H bonds, facilitating the use of nonprecious metal catalysts in demanding transformations. Notably, aerobic C-H carbonylation of methane to acetic acid remains formidable due to the rapid oxidation of methyl radicals, producing undesired C1 oxygenates. We present an iron terpyridine catalyst utilizing LMCT to achieve exceptional C2/C1 selectivity through synergistic photoexcitation, methyl radical generation, and carbonylation. Mechanistic studies highlight the critical roles of Fe(II) and Fe-carbonyl complexes in bypassing methyl radical oxidation via a radical rebound-like pathway, unlocking unprecedented efficiency in methane aerobic carbonylation.

Selective Arene Photonitration via Iron-Complex β-Homolysis

Nitroaromatics, as an important member and source of nitrogen-containing aromatics, is bringing enormous economic benefits in fields of pharmaceuticals, dyes, pesticides, functional materials, fertilizers, and explosives. Nonetheless, the notoriously polluting nitration industry, which suffers from excessive discharge of fumes and waste acids, poor functional group tolerance, and tremendous purification difficulty, renders mild, efficient, and environmentally friendly nitration a formidable challenge. Herein, we develop a visible-light-driven biocompatible arene C-H nitration strategy with good efficiency and regioselectivity, marvelous substrate applicability and functional group tolerance, and wide application in scale-up synthesis, total synthesis, and late-stage functionalization. A nitryl radical delivered through unusual β-homolysis of a photoexcited ferric-nitrate complex is proposed to be the key nitrification reagent in this system.

Photoelectrocatalytic [4+2] Annulation for S-Heterocycle Assembly Enabled by Proton-Coupled Electron Transfer (PCET)

Cross-dehydrogenative couplings (CDC) present an efficient strategy for the assembly of biorelevant heterocycles, but are thus far largely limited to toxic transition metals and rather harsh reaction conditions. In sharp contrast, we, herein report on a mild photoelectrocatalyzed CDC-[4+2] annulation enabling the synthesis of functionalized isothiochromenes enabled by a proton-coupled electron transfer (PCET) strategy. The transformative photoelectrocatalysis obviated toxic transition-metal, high reaction temperatures, and stoichiometric chemical redox reagents. This approach was characterized by exceedingly mild conditions, ample substrate scope, and a commercially available catalyst. Gram-scale reactions and a telescoped synthesis route reflected the unique potential in the green synthesis of important S-heterocycles.

Bifunctional iron-catalyzed alkyne Z-selective hydroalkylation and tandem Z-E inversion via radical molding and flipping

The challenging synthesis of thermodynamic-unfavored cis-olefins through catalytic cross-coupling reactions requires the synergistic interaction of substrate-activating units and configuration-regulating catalysts. Successfully hitting these two birds with one stone, we herein develop a convenient photoredox access to Z-alkenes from alkynes and light alkanes with a bifunctional iron-catalyzed system possessing both C(sp3)-H activation and configuration-controlling abilities. The protocol exhibits 100% atom utilization, mild conditions, a broad substrate scope, and compatibility with multitudinous functional groups. The detailed reaction mechanism and the origin of geometry regulation are well investigated by experimental and computational studies. Progressively, a catalytic amount of diaryl disulfides is introduced for consecutive photoinduced Z-E isomerization via reversible radical addition and flipping. Big steric hindrance substituents assembled on the disulfide emerge necessity for suppressing double-bond migration. This tandem strategy paves a promising way for stereoselective alkene construction and will bring significant inspiration for the development of transition metal photocatalysis.

Transforming cyclopropanes to enamides via σ-C-C bond eliminative borylation

Recent strides in C-H borylation have significantly expanded our toolkit for the preparation of organoboronates. Nevertheless, avenues alternative to obtain these compounds via σ-C-C cleavage, thereby facilitating molecular scaffold editing, remain scarce. Several methodologies have been proposed for hydroboration of cyclopropanes by activating C-C bonds, conventionally relying on noble and hazardous metal catalysts to control reaction outcomes. Here, we present a strategy for crafting stereochemically precise γ-borylenamides through ring-opening of cyclopropanes avoiding any metallic entities. Boryl species, generated through a ternary reaction with BCl3, cyclopropanes, and a tertiary amine, selectively undergo C-C bond eliminative borylation under the directing of N-acyl group, thereby ensuring enhanced selectivity and efficiency along the reaction pathway. Such inherently stereoconvergent approach accommodates precursors of diverse geometries, including cis/trans isomeric blends.

Site-Selective Distal C(sp3)-H Bromination of Aliphatic Amines as a Gateway for Forging Nitrogen-Containing sp3 Architectures

Herein, we disclose a new strategy that rapidly and reliably incorporates bromine atoms at distal, secondary C(sp3)-H sites in aliphatic amines with an excellent and predictable site-selectivity pattern. The resulting halogenated building blocks serve as versatile linchpins to enable a series of carbon-carbon and carbon-heteroatom bond-formations at remote C(sp3) sites, thus offering a new modular and unified platform that expediates the access to advanced sp3 architectures possessing valuable nitrogen-containing saturated heterocycles of interest in medicinal chemistry settings.

Iron-Catalyzed Photoredox Alcohol α-C-H Alkylation and Tandem Intramolecular Cyclization: Facile Access to Multisubstituted 2,3-Dihydrofurans and γ-Butyrolactones

Multisubstituted furans occupy a pivotal position within the realms of synthetic chemistry and pharmacological science due to their distinctive chemical configurations and inherent properties. We herein introduce a tandem difunctionalization protocol of alcohols for the efficient synthesis of multisubstituted 2,3-dihydrofurans and γ-butyrolactones through the combination of photocatalysis and iron catalysis under mild conditions. Photoredox alcohol α-C(sp3)-H activation and Pinner-type intramolecular cyclization are two key processes. This method features significant convenience, economic benefits, and environmental friendliness.

Boronyl-Group-Assisted Decatungstate-Catalyzed Benzylic C(sp3)-H Alkylation

Boronic acid synthesis primarily involves the introduction of boronyl groups. However, an alternative route that involves the functionalization of boronic acids has not received much attention. This study describes the catalytic C(sp3)-H alkylation of ortho-tolylboronic acids utilizing the interaction between a free boronyl group [-B(OH)2] and a decatungstate photocatalyst [W10O32]4-. The boronyl groups of the alkylated products could be converted without isolation of the alkylated product.

Time for growth

Plants measure the duration of metabolic activity to promote rapid growth in long days.