Aerobic redox deracemization of α-aryl glycine esters

Chen, Xiaohan; Yan, Lei; Zhang, Lu; Zhao, Changyin; Feng, Guidong; Chen, Lei; Sun, Shutao; Liu, Qingyun; Liu, Lei

doi:10.1016/j.tetlet.2020.152107

Cited by 8 publications

(7 citation statements)

References 49 publications

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“…In this context, a number of enantioselective catalytic methods have been established, especially for the synthesis of non‐commercially available variants [37,38] . Among them, stoichiometric oxidant‐ and reductant‐dependent two‐step catalytic deracemization [39] of N ‐aryl α‐amino esters was recently reported by Liu and co‐workers [40,41] . We speculated that redox‐neutral photocatalysis would be a viable protocol that can effectively surmount the poor atom and step economy (Scheme 2A).…”

Section: Resultsmentioning

confidence: 99%

“…[37,38] Among them, stoichiometric oxidant-and reductant-dependent two-step catalytic deracemization [39] of N-aryl α-amino esters was recently reported by Liu and co-workers. [40,41] We speculated that redox-neutral photocatalysis would be a viable protocol that can effectively surmount the poor atom and step economy (Scheme 2A). The reaction is designed to be triggered by single-electron oxidation of the N atom in the ground-state amino esters by the activated photosensitizer (*PC), thereby offering amine cation radicals A, which can further generate radicals B.…”

Section: Resultsmentioning

confidence: 99%

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Deracemization through Sequential Photoredox‐Neutral and Chiral Brønsted Acid Catalysis

Zhang

et al. 2022

Angewandte Chemie

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

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Deracemization through Sequential Photoredox‐Neutral and Chiral Brønsted Acid Catalysis

Zhang

et al. 2022

Angewandte Chemie

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“…The use of benzothiazoline (BTZ) as the reductant is beneficial to the exclusive chemoselectivity at the CN bond over that at the CC bond in an oxidized alkynyl imine intermediate. β,γ-Alkenyl α-amino esters together with α-aryl glycine esters are also competent substrates …”

Section: Hydride-abstraction-initiated Redox Deracemizationmentioning

confidence: 99%

“…β,γ-Alkenyl α-amino esters together with α-aryl glycine esters are also competent substrates. 40 We next explored redox deracemization of the stereocenters adjacent to electron-withdrawing groups (Scheme 20). In 2020, we reported the redox deracemization of tertiary stereocenters adjacent to a series of electron-withdrawing groups including perfluoroalkyl, cyano, and ester moieties.…”

Section: Hydride-abstraction-initiated Redox Deracemizationmentioning

confidence: 99%

Hydride-Abstraction-Initiated Catalytic Stereoselective Intermolecular Bond-Forming Processes

Liu

2022

Acc. Chem. Res.

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Conspectus The stereoselective intermolecular bond-forming reactions through the direct manipulation of ubiquitous yet inert C(sp3)–H bonds represent an important and long-standing goal in chemistry. In particular, developing such a stereoselective bimolecular transformation involving carbocation intermediates generated via site-selective hydride abstraction or formal hydride abstraction by organic oxidants would avoid the preinstallation of directing groups and is therefore attractive. Hydride-abstraction-initiated bimolecular transformations have received considerable attention, but existing examples lack stereoselective studies. Prevalent stereoselective studies typically suffer from the narrow substrate scope of specific and highly reactive N-aryl amines and diarylmethanes together with limited synthetic utility. This Account describes our recent advances in the development and synthetic application of hydride-abstraction-initiated stereoselective intermolecular C–C and C–H bond-forming processes with significantly expanded scopes involving structurally diverse N-acyl amines and ethers together with nitriles, esters, and perfluoroalkyl moieties. We first explored hydride-abstraction-initiated stereoselective intermolecular C–C bond-forming processes. Utilizing triarylmethyl cations or oxoammonium ions as hydride abstractors, we accomplished the diastereoselective oxidative C–H functionalization of structurally diverse N-acyl amines and ethers with a range of organoboranes and C–H components, efficiently installing a series of alkyl, alkenyl, aryl, and alkynyl species into the α-position of heteroatoms with good levels of diastereocontrol. Subsequently, we developed an “acetal pool” strategy as the toolbox to regulate the stability of cationic intermediates and the compatibility of organic oxidants with a delicate asymmetric catalysis system. Utilizing this strategy, we achieved the catalytic enantioselective oxidative C–H alkenylation, arylation, alkynylation, and alkylation of diverse N-acyl heterocycles with a range of boronates and C–H components. Simultaneously, we extended this strategy to the asymmetric oxidative C–H alkylation of ethers. Notably, the method allows solvents that are used daily, such as tetrahydrofuran, tetrahydropyran, and diethyl ether, to be facilely transformed to high-value-added optically pure bioactive molecules. We further expanded the scope of this challenging area from the C(sp3)–H bond adjacent to electron-donating heteroatoms to valuable electron-withdrawing functional groups including nitriles, esters, and perfluoroalkyl moieties for the stereoselective construction of single and vicinal quaternary carbon stereocenters, respectively. We studied hydride-abstraction-initiated catalytic asymmetric intermolecular C–H bond-forming processes, known as redox deracemization. Utilizing the acetal pool strategy, we reported the first redox deracemization of cyclic benzylic ethers. Later, we disclosed an aerobic one-pot deracemization of diverse α-amino acid derivatives with excellent ...

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“…The combination of Hantzsch ester 7a and chiral imidodiphosphoric acid cat-2a was chosen to facilitate asymmetric reduction. This elegant protocol enables effective deracemizations of an impressive list of substrates including heterocyclic esters, 53 compounds with α-alkynyl tertiary stereocenters, 54,55 α-aryl glycine esters, 56 and dihydropyrimidines. 57 Besides a stepwise reaction sequence, spatial separation was proven to be efficient for chemocatalytic deracemization.…”

Section: ■ Introductionmentioning

confidence: 99%

Catalytic Deracemization Reactions

et al. 2023

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

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Aerobic redox deracemization of α-aryl glycine esters

Cited by 8 publications

References 49 publications

Deracemization through Sequential Photoredox‐Neutral and Chiral Brønsted Acid Catalysis

Deracemization through Sequential Photoredox‐Neutral and Chiral Brønsted Acid Catalysis

Hydride-Abstraction-Initiated Catalytic Stereoselective Intermolecular Bond-Forming Processes

Catalytic Deracemization Reactions

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