Mechanochemical Direct Fluorination of Unactivated C(<i>sp</i><sup>3</sup>)−H Bonds

Min, Sehye; Park, Beomsoon; Nedsaengtip, Jantakan; Hong, Soon Hyeok

doi:10.1002/adsc.202200206

Cited by 13 publications

(8 citation statements)

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“…Mechanochemical method is recently applied to the direct fluorination of unactivated C(sp 3 )–H bonds using N‐fluorobenzenesulfonimide (NFSI) as both HAT precursor and fluorine source as reported by the Hone research group (Scheme 18). [ 70 ] The mechanical force‐induced homolytic cleavage of the N—F bond is proposed. The generated N‐centered imidyl radical then abstracts a hydrogen atom from aliphatic C—H bond followed by fluorination with NFSI.…”

Section: Electrophilic Fluorination Reagentsmentioning

confidence: 99%

Recent Advances in C—F Bond Formation from Carbon‐Centered Radicals

Zhang,

Wang,

Cheng

2024

Chin. J. Chem.

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Comprehensive SummaryConstruction of C–F bonds is a direct and efficient method for introducing fluorine into pharmaceuticals, agrochemicals, and materials. Strategies such as nucleophilic, electrophilic, radical, and transition‐metal catalyzed fluorination have been developed to meet the demand of diverse C–F bond formation. Among them, radical fluorination has been witnessed with substantial advancement in a recent decade. Herein, we reviewed methods for formation of C–F bonds with carbon‐centered radicals as key intermediates, especially in recent five years. We introduce in the paper with different fluorinating reagents, strategies for radical generation, and application in late‐stage functionalization and synthesis of PET tracers. We also indicate the current limitations and propose the direction of the field for the future development.This article is protected by copyright. All rights reserved.

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Section: Electrophilic Fluorination Reagentsmentioning

confidence: 99%

Recent Advances in C—F Bond Formation from Carbon‐Centered Radicals

Zhang,

Wang,

Cheng

2024

Chin. J. Chem.

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“…Reaction between (NH 4 ) 2 S 2 O 8 (3.0 equiv), phenylacetic acid (10), K 3 PO 4 (2.0 equiv), and TEMPO (2.0 equiv) at 40 Hz for 6 h gave a TEMPO-trapped species 11 in 11% yield. Similarly, when substituted benzaldehyde (12) was employed, another TEMPO-trapped species (13) was obtained in 18% yield. Notably, the formation of 13 is suggestive of a HAT process by in situ generated SO 4…”

Section: Organicmentioning

confidence: 99%

“…Since acids are incompatible with SS materials, we purposely selected PP milling tubes and zirconia (ZrO 2 ) balls instead of the more popular SS jars and balls in this work to avoid potential metal leaching (Table S5). 12 Given that 4-bromoquinoline (2a) is more economical, reaction optimization proceeded with 2a. When TsOH•H 2 O was applied to the optimized conditions, coupling product 3a was obtained in 75% yield (Table 1, entry 1).…”

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confidence: 99%

Solvent-Free Mechanoradical-Mediated Minisci-Type C–H Alkylation of N-Heteroarenes

Gu,

Wang,

Yan

2023

Org. Lett.

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An environmentally friendly new C−H alkylation method of N-heteroarenes facilitated by mechanochemistry is described. Under solvent-free ball-milling, mechanoradicals (SO 4•− ) were generated from persulfate via in situ homolysis in the solid state, at as low as −50 °C. These highly oxidizing radicals readily transform alkyl trifluoroborate salts to their corresponding carbon-based radicals for subsequent C−C bond formation with N-heterocycles. Mechanistic studies unambiguously confirmed the involvement of both oxygen-and alkyl-radical-based intermediates.R adical reactions are generally initialized by heat, light, and chemical approaches (Scheme 1a). 1 Due to the harsh conditions often needed to form these open shell species, radical reactions were once considered too reactive and unselective. In the past 15 years, methodologies deriving from drastically mild conditions have been developed, notably through visible light photoredox catalysis 2 and electrocatalysis, 3 unleashing the unique synthetic values in radical chemistry, and they have now become a powerful tool in modern organic synthesis.Mechanochemistry, more specifically ball-milling, has gained renewed interests in polymer chemistry and organic synthesis. 4,5 Being solvent-free, solvent screening and other solvent-required operations in solvent-phase reactions are avoided to save time and cost and enhance sustainability. Mechanical force can also be applied to generate free radicals, known as mechanoradicals. Since a century ago, Staudinger, Sohma, and others had discovered that polymers undergo chain scission upon mechanical stimulation through homolytic pathways. 6,7 Recently, using this strategy, the formation of fluorescent polymers from commodity polymers was reported. 7d,8 Given the widespread applications in both radical chemistry and mechanochemistry, we strive to develop processes merging these two areas together, more specifically, to investigate how a radical is generated in the solid state and if new types of bondformation/-breaking reactions and/or reaction mechanisms (distinct from solution-phase reactions) can be discovered. Despite the long history of mechanoradicals, implementing this force-directed concept in organic synthesis, especially in C−H activation and C−C bond-formation reactions, is relatively unexplored. 9,10 Recently, Ito 9b and Bolm 9f elegantly demon-

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“…The oxidation of hydrocarbons into value-added chemical products, especially alkanes that are much more difficult to utilize without active functional groups, is of great importance in the chemical industry. − Cyclohexane oxidation is a typical hydrocarbon resource high-value utilization process, and in this process, the oxidation products including cyclohexanol, cyclohexanone (referred to as KA oil), and adipic acid are important organic intermediates for nylon-6 and nylon-66 in the nylon industry. ,− For the details of cyclohexane oxidation, the widely accepted oxidation process of cyclohexane includes the activation of cyclohexane to a cyclohexyl radical, the transition to KA oil, the further oxidation to adipic acid, and the over oxidation to glutaric acid, succinic acid, and other byproducts, as described in Scheme (b). − As a complex radical oxidation reaction, it is a great challenge to activate the C–H bond and to generate active radicals under proper conditions due to the strong and inert C–H bonds, and on the other hand, it is also an important issue to investigate in order to control the oxidation process to realize the production of target products under high selectivity and avoid over oxidations. − …”

Section: Introductionmentioning

confidence: 99%

Roles of Oxygen Vacancies in CeO₂ Nanostructures for Catalytic Aerobic Cyclohexane Oxidation

et al. 2023

ACS Appl. Nano Mater.

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Nanostructured cerium-based catalytic materials have attracted much attention in the field of redox catalysis, due to the excellent active sites exposed on the nanocrystal surface, and herein, the oxygen vacancy (O V ) and the crystal facet effect of typical model nanostructured ceria (Nano-CeO 2 ) were focused and investigated for the catalytic aerobic cyclohexane oxidation. Specifically for the CeO 2 nanocubes with a {100} facet, the CeO 2 nanopolyhedrons with a dominant {111} facet, and the CeO 2 nanorods with a dominant {110} facet, the catalytic roles of the O V and acid sites toward cyclohexane oxidation were systematically investigated. Surface oxygen vacancy (Sur-O V ) and intrinsic oxygen vacancy (Int-O V ), and particularly the active Sur-O V and active Int-O V performing catalytic activity under a working state specific for cyclohexane oxidation, were accurately recognized and distinguished. Furthermore, the activation ability of the O V sites for activating molecular oxygen into active oxygen species (O Active ) was also revealed, and the acid site properties, which include the acidity and the types of acid sites, were probed and quantified. The Nano-CeO 2 with an exposed {100} facet possesses the most active Sur-O V , determining the catalytic activity, and has the strongest activation ability, contributing to a high reaction activity under extremely inert conditions. The Nano-CeO 2 with a {110} dominant facet with the most active Int-O V and abundant acid sites could accelerate further oxidation to adipic acid; the effect of the two key sites was described particularly by the α factor (= Total Acidity × Amount of Active Int-O V ). Finally, the property−performance relationship toward cyclohexane oxidation was speculated based on the Nano-CeO 2 catalytic system.

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Mechanochemical Direct Fluorination of Unactivated C(sp³)−H Bonds

Cited by 13 publications

References 103 publications

Recent Advances in C—F Bond Formation from Carbon‐Centered Radicals

Recent Advances in C—F Bond Formation from Carbon‐Centered Radicals

Solvent-Free Mechanoradical-Mediated Minisci-Type C–H Alkylation of N-Heteroarenes

Roles of Oxygen Vacancies in CeO₂ Nanostructures for Catalytic Aerobic Cyclohexane Oxidation

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Mechanochemical Direct Fluorination of Unactivated C(sp3)−H Bonds

Cited by 13 publications

References 103 publications

Recent Advances in C—F Bond Formation from Carbon‐Centered Radicals

Recent Advances in C—F Bond Formation from Carbon‐Centered Radicals

Solvent-Free Mechanoradical-Mediated Minisci-Type C–H Alkylation of N-Heteroarenes

Roles of Oxygen Vacancies in CeO2 Nanostructures for Catalytic Aerobic Cyclohexane Oxidation

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Mechanochemical Direct Fluorination of Unactivated C(sp³)−H Bonds

Roles of Oxygen Vacancies in CeO₂ Nanostructures for Catalytic Aerobic Cyclohexane Oxidation