Energy transfer-enabled unsymmetrical diamination using bifunctional nitrogen-radical precursors

Tan, Guangying; Das, Mowpriya; Kleinmans, Roman; Katzenburg, Felix; Daniliuc, Constantin G.; Glorius, Frank

doi:10.1038/s41929-022-00883-3

Cited by 50 publications

(26 citation statements)

References 65 publications

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“…Along these lines, we reasoned that based on our expertise in EnT-mediated sigma-bond homolysis toward difunctionalization of alkenes − and the inherent weak N–S bond strength (≈ 70 kcal mol –1 ) 3 could serve as an excellent reagent toward the synthesis of racemic β-imino sulfonyl fluorides (Figure C). The N-protecting group would permit intermolecular SuFEx, while deprotection and cyclization with the adjacent sulfonyl fluoride group would give rise to β-sultams.…”

Section: Introductionmentioning

confidence: 99%

EnT-Mediated N–S Bond Homolysis of a Bifunctional Reagent Leading to Aliphatic Sulfonyl Fluorides

et al. 2023

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Sulfur(VI) fluoride exchange (SuFEx) gives rise to a plethora of high-valent sulfur linkages; however, the availability of (aliphatic) sulfonyl fluoride manifolds lag behind, owing to the limited sources of introducing the SO2F moiety via a classical two-electron approach. Recently, radical-based methodologies have emerged as a complementary strategy to increase the diversity of accessible click partners. In this work, synthesis of a bench-stable sulfamoyl fluoride reagent is presented, which may undergo sigma-bond homolysis upon visible-light-induced sensitization to form protected β-amino sulfonyl fluorides from alkene feedstocks. Notably, this offers an appealing strategy to access various building blocks for peptido sulfonyl fluorides, relevant in a medicinal chemistry context, as well as an intriguing entry to β-ammonium sulfonates and β-sultams, from alkenes. Densely functionalized 1,3-sultones were obtained by employing allyl alcohols as substrates. Surprisingly, allyl chloride-derived β-imino sulfonyl fluoride underwent S–O bond formation and ring closure to yield rigid cyclopropyl β-imino sulfonate ester under SuFEx conditions. Furthermore, by engaging a thiol-based hydrogen atom donor in the reaction, the reactivity of the same reagent can be tuned toward the direct synthesis of aliphatic sulfonyl fluorides. Mechanistic experiments indicate an energy transfer (EnT)-mediated process. The transient sulfonyl fluoride radical adds to the alkene and product formation occurs upon either radical–radical coupling or hydrogen atom transfer (HAT), respectively.

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Section: Introductionmentioning

confidence: 99%

EnT-Mediated N–S Bond Homolysis of a Bifunctional Reagent Leading to Aliphatic Sulfonyl Fluorides

et al. 2023

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“…Photocatalysis has become an essential tool in organic synthesis, sustainably expanding the chemical space of accessible molecules for drug discovery and materials science. − Triplet-triplet energy transfer (EnT) processes are particularly important as they allow access to triplet excited states of small molecules that are otherwise impossible to access directly through irradiation with visible light. , Using these approaches, novel radical-based disconnections and nontraditional coupling reactions have recently been discovered with high specificity, selectivity, and efficiency. − …”

Section: Introductionmentioning

confidence: 99%

Imidazophenothiazine-Based Thermally Activated Delayed Fluorescence Materials with Ultra-Long-Lived Excited States for Energy Transfer Photocatalysis

Hojo,

Bergmann,

Elgadi

et al. 2023

J. Am. Chem. Soc.

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Triplet-triplet energy transfer (EnT) is a powerful activation pathway in photocatalysis that unlocks new organic transformations and improves the sustainability of organic synthesis.Many current examples, however, still rely on platinum-group metal complexes as photosensitizers, with associated high costs and environmental impacts. Photosensitizers that exhibit thermally activated delayed fluorescence (TADF) are attractive fully organic alternatives in EnT photocatalysis. However, TADF photocatalysts incorporating heavy atoms remain rare, despite their utility in inducing efficient spin-orbit-coupling, intersystem-crossing, and consequently a high triplet population. Here, we describe the synthesis of imidazophenothiazine (IPTZ), a sulfur-containing heterocycle with a locked planar structure and a shallow LUMO level. This acceptor is used to prepare seven TADF-active photocatalysts with triplet energies up to 63.9 kcal mol −1 . We show that sulfur incorporation improves spin-orbit coupling and increases triplet lifetimes up to 3.64 ms, while also allowing for tuning of photophysical properties via oxidation at the sulfur atom. These IPTZ materials are applied as photocatalysts in five seminal EnT reactions: [2 + 2] cycloaddition, the disulfide-ene reaction, and Ni-mediated C−O and C−N cross-coupling to afford etherification, esterification, and amination products, outcompeting the industry-standard TADF photocatalyst 2CzPN in four of the five studied scenarios. Detailed photophysical and theoretical studies are used to understand structure−activity relationships and to demonstrate the key role of the heavy atom effect in the design of TADF materials with superior photocatalytic performance.

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“…In recent years, photoredox-catalyzed reactions have been extensively explored in organic synthesis; − especially, visible-light-mediated dearomatization strategies have been employed as appealing alternatives for synthesis of heterocyclic frameworks. − A series of aromatic compounds, such as indole, − benzofuran, and benzothiophene, have been achieved in intermolecular or intramolecular dearomatization processes by the visible light irradiation (Scheme b). However, generally speaking, the current research mainly focuses on aromatic heterocycles containing only one heteroatom, especially indole and its derivatives; other heteroaromatic rings containing two heteroatoms are relatively less explored.…”

Section: Introductionmentioning

confidence: 99%

Iron-Catalyzed Photoredox Intermolecular Dearomatization of Benzothiazoles with Alkanes

Xu,

Peng,

Chen

et al. 2023

ACS Sustainable Chem. Eng.

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Benzothiazolines, with their versatile nature, serve as fundamental building blocks for the synthesis of significant biological compounds. However, methods for the preparation of benzothiazolines from readily available starting materials are limited. An efficient synthesis of benzothiazoline via photoredox-catalyzed dearomatization of benzothiazole derivatives has been achieved at room temperature. This catalysis proceeds via a ligand to metal charge transfer process, and FeCl 3 plays a dual role as an indirect HAT reagent and reducing agent. This methodology can be conveniently scaled up, and most of the alkylated products can be purified without chromatography. In addition, this process exhibited the advantages of low cost, high reaction efficiency, and mild conditions.

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Energy transfer-enabled unsymmetrical diamination using bifunctional nitrogen-radical precursors

Cited by 50 publications

References 65 publications

EnT-Mediated N–S Bond Homolysis of a Bifunctional Reagent Leading to Aliphatic Sulfonyl Fluorides

EnT-Mediated N–S Bond Homolysis of a Bifunctional Reagent Leading to Aliphatic Sulfonyl Fluorides

Imidazophenothiazine-Based Thermally Activated Delayed Fluorescence Materials with Ultra-Long-Lived Excited States for Energy Transfer Photocatalysis

Iron-Catalyzed Photoredox Intermolecular Dearomatization of Benzothiazoles with Alkanes

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