Energy transfer photocatalysis: exciting modes of reactivity

Chemical Society Reviews, Год журнала: 2024, Номер 53(3), С. 1068 - 1089

Опубликована: Янв. 1, 2024

Leveraging light energy to expose the ‘dark’ reactive states describes whole essence of triplet–triplet transfer. This offers an impressive opportunity conduct a multitude diverse reactions and access sought-after molecular motifs.

Язык: Английский

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Light-empowered contra-thermodynamic stereochemical editing

Nature Reviews Chemistry, Год журнала: 2022, Номер 7(1), С. 35 - 50

Опубликована: Ноя. 16, 2022

Язык: Английский

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Light-enabled deracemization of cyclopropanes by Al-salen photocatalysis

Nature, Год журнала: 2023, Номер 621(7980), С. 753 - 759

Опубликована: Авг. 23, 2023

Privileged chiral catalysts-those that share common structural features and are enantioselective across a range of reactions-continue to transform the chemical-research landscape1. In recent years, new reactivity modes have been achieved through excited-state catalysis, processes activated by light, but it is unclear if selectivity ground-state privileged catalysts can be matched. Although interception photogenerated intermediates cycles has partially addressed this challenge2, single, photocatalysts simultaneously regulate conspicuously scarce3. So far, precision donor-acceptor recognition motifs remain crucial in photocatalyst design4. Here we show Al-salen complexes, which well-defined photophysical properties, used for efficient photochemical deracemization5 cyclopropyl ketones (up 98:2 enantiomeric ratio (e.r.)). Irradiation at λ = 400 nm (violet light) augments commercial catalyst enable enantioselectivity regulated simultaneously. This circumvents need tailored catalyst-substrate motifs. It predicted study will stimulate re-evaluation many venerable (ground-state) processes, ultimately leading identification candidates may considered 'privileged' both models.

Язык: Английский

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Multiplicative enhancement of stereoenrichment by a single catalyst for deracemization of alcohols

Science, Год журнала: 2023, Номер 382(6669), С. 458 - 464

Опубликована: Окт. 26, 2023

Stereochemical enrichment of a racemic mixture by deracemization must overcome unfavorable entropic effects as well the principle microscopic reversibility; recently, photochemical reaction pathways unveiled energetic input light have led to innovations toward this end, most often ablation stereogenic C(sp3)-H bond. We report photochemically driven protocol in which single chiral catalyst two mechanistically different steps, C-C bond cleavage and formation, achieve multiplicative enhancement stereoinduction, leads high levels stereoselectivity. Ligand-to-metal charge transfer excitation titanium coordinated phosphoric acid or bisoxazoline efficiently enriches alcohols that feature adjacent fully substituted centers enantiomeric ratios up 99:1. Mechanistic investigations support pathway sequential radical-mediated scission formation through common prochiral intermediate reveal that, although overall stereoenrichment is high, selectivity each individual step moderate.

Язык: Английский

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Deracemization through Sequential Photoredox‐Neutral and Chiral Brønsted Acid Catalysis

Angewandte Chemie International Edition, Год журнала: 2022, Номер 61(49)

Опубликована: Окт. 17, 2022

Abstract Catalytic deracemization is an ideal synthetic strategy due to its formally perfect atom utilization. Asymmetric photocatalysis has been appreciated as a promising tool accomplish this attractive reaction pattern in economical fashion, but it remains underdeveloped. Here, we report new platform based on photoredox‐neutral catalysis, allowing efficient and modular optical enrichment of α‐amino esters other valuable analogues. Two single‐electron transfer processes between the photocatalyst substrates serve provide key prochiral intermediates, chiral Brønsted acid catalyst mediates enantioselective protonation reconstitute stereogenic C−H bond. The efficiency determined by enantiofacial differentiation effect during stereocentre‐forming step.

Язык: Английский

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Catalytic Deracemization Reactions

Journal of the American Chemical Society, Год журнала: 2023, Номер 145(20), С. 10917 - 10929

Опубликована: Май 13, 2023

Deracemization, which converts a racemate into its single enantiomer without separation of the intermediate, has gained renewed interest in asymmetric synthesis with inherent atomic economy and high efficiency. However, this ideal process requires selective energy input delicate reaction design to surmount thermodynamical kinetical constraints. With rapid development catalysis, many catalytic strategies concert exogenous have been exploited facilitate nonspontaneous enantioenrichment. In perspective, we will discuss basic ideas accomplish deracemization, categorized by three major sources including chemical (redox)-, photo- mechanical from attrition. Emphasis be given features underlying deracemization mechanism together perspectives on future development.

Язык: Английский

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Direct Observation of Triplet States in the Isomerization of Alkenylboronates by Energy Transfer Catalysis

Journal of the American Chemical Society, Год журнала: 2023, Номер 145(39), С. 21576 - 21586

Опубликована: Сен. 20, 2023

Alkenylboronates are versatile building blocks for stereocontrolled synthesis owing to the traceless nature of boron group that can be leveraged achieve highly selective geometric isomerization. Using thioxanthone as an inexpensive photocatalyst, photoisomerization these species continues provide expansive platform stereodivergent synthesis, particularly in construction bioactive polyenes. Although mechanistic investigations consistent with light-driven energy transfer, direct experimental evidence remains conspicuously absent. Herein, we report a rigorous investigation using two widely used alkenylboronates alongside relevant reference compounds. Through combination irradiation experiments, transient absorption spectroscopic studies, kinetic modeling, and DFT calculations all isomers model compounds, it has been possible unequivocally detect characterize perpendicular triplet generated by transfer. Our results serve not only blueprint studies challenging organic sensitizers, but guidelines delineated have also enabled development more sustainable reaction conditions: first time, efficient organocatalytic isomerization under sunlight become feasible.

Язык: Английский

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Multifaceted View on the Mechanism of a Photochemical Deracemization Reaction

Journal of the American Chemical Society, Год журнала: 2023, Номер 145(4), С. 2354 - 2363

Опубликована: Янв. 20, 2023

Upon irradiation in the presence of a chiral benzophenone catalyst (5 mol %), racemic mixture given imidazolidine-2,4-dione (hydantoin) can be converted almost quantitatively into same compound with high enantiomeric excess (80-99% ee). The mechanism this photochemical deracemization reaction was elucidated by suite mechanistic experiments. It corroborated nuclear magnetic resonance titration that binds two enantiomers two-point hydrogen bonding. In one diastereomeric complexes, atom at stereogenic carbon is ideally positioned for transfer (HAT) to photoexcited benzophenone. Detection protonated ketyl radical transient absorption revealed abstraction occur from only but not other hydantoin enantiomer. Quantum chemical calculations allowed us visualize HAT within complex and, more importantly, showed back does its oxygen atom. achiral enol formed process could directly monitored characteristic signal λ ≅ 330 nm. Subsequent tautomerization leads both enantiomers, them returns catalytic cycle, thus leading an enrichment data are fully consistent deuterium labeling experiments and deliver detailed picture synthetically useful reaction.

Язык: Английский

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Catalytic Photochemical Deracemization via Short‐Lived Intermediates

Angewandte Chemie International Edition, Год журнала: 2023, Номер 62(50)

Опубликована: Июль 10, 2023

Upon irradiation in the presence of a suitable chiral catalyst, racemic compound mixtures can be converted into enantiomerically pure compounds with same constitution. The process is called photochemical deracemization and involves formation short-lived intermediates. By opening different reaction channels for forward to intermediate re-constitution molecule, entropically disfavored becomes feasible. Since discovery first 2018, field has been growing rapidly. This review comprehensively covers research performed area discusses current developments. It subdivided according mode action respective substrate classes. focus this on scope individual reactions discussion mechanistic details underlying presented reaction.

Язык: Английский

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Photoexcited Palladium-Catalyzed Deracemization of Allenes

Journal of the American Chemical Society, Год журнала: 2024, Номер 146(30), С. 21137 - 21146

Опубликована: Июль 18, 2024

The different enantiomers of specific chiral molecules frequently exhibit disparate biological, physiological, or pharmacological properties. Therefore, the efficient synthesis single is particular importance not only to pharmaceutical sector but also other industrial sectors, such as agrochemical and fine chemical industries. Deracemization, a process during which racemic mixture converted into nonracemic product with 100% atom economy theoretical yield, most straightforward method access enantioenriched challenging task due decrease in entropy microscopic reversibility. Axially allenes bear distinctive structure two orthogonal cumulative π-systems are acknowledged synthetically versatile synthons organic synthesis. selective creation axially high optical purity under mild reaction conditions has always been very popular hot topic remains challenging. Herein, photoexcited palladium-catalyzed deracemization nonprefunctionalized disubstituted disclosed. This provides an economical strategy accommodate broad scope good enantioselectivities yields (53 examples, up 96% yield 95% ee). use suitable palladium complex visible light irradiation essential factor achieving this transformation. A metal-to-ligand charge transfer mechanism was proposed based on control experiments density functional theory calculations. Quantum mechanical studies implicate dual modes asymmetric induction behind our new protocol: (1) sterically controlled stereoselective binding one allene enantiomer ground-state (2) facile, noncovalent interaction-driven excited-state isomerization toward opposite enantiomer. success newly established photochemical should provide inspiration for expansion multisubstituted will open mode enantioselective catalysis.

Язык: Английский

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