Beyond esoteric interest, organocatalysis has now become one major pillar of asymmetric catalysis. Here, we discuss how new activation modes are conquering challenging stereoselective transformations ...and the recent integration of organocatalysis with emerging photo- and electrocatalysis, as well as artificial intelligence.Organocatalysis has become a major pillar of (asymmetric) catalysis. Here, the authors discuss recent trends in organocatalytic activation modes for challenging stereoselective transformations and the emerging integration with other fields, such as photoredox catalysis and electrosynthesis.
Atropisomerism is a stereochemical behavior portrayed by three-dimensional molecules that bear rotationally restricted σ bond. Akin to the well-represented point-chiral molecules, atropisomerically ...chiral compounds are finding increasing utilities in many disciplines where molecular asymmetry is influential. This provides steady demand on atroposelective synthesis, where numerous synthetic pursuits have been rewarded with conceptually novel and streamlined methods while expanding the structural diversity of atropisomers. This review summarizes key achievements in stereoselective preparation of biaryl, heterobiaryl, and nonbiaryl atropisomers documented between 2015 and 2020. Emphasis is placed on the synthetic strategies for each structural class, while examples are cited to illustrate the potential applications of the accessed atropochiral targets.
The Ugi reaction constructs α-acylaminoamide compounds by combining an aldehyde or ketone, an amine, a carboxylic acid, and an isocyanide in a single flask. Its appealing features include inherent ...atom and step economy together with the potential to generate products of broad structural diversity. However, control of the stereochemistry in this reaction has proven to be a formidable challenge. We describe an efficient enantioselective four-component Ugi reaction catalyzed by a chiral phosphoric acid derivative that delivers more than 80 α-acylaminoamides in good to excellent enantiomeric excess. Experimental and computational studies establish the reaction mechanism and origins of stereoselectivity.
Conspectus The growing importance of axially chiral architectures in different scientific domains has unveiled shortcomings in terms of efficient synthetic access and skeletal variety. This account ...describes our strategies in answering these challenges within the organocatalytic context where the emergence of bifunctional catalysts such as chiral phosphoric acids (CPAs) has proven invaluable in controlling the sense of axial chirality. The wide occurrence of bi(hetero)aryl skeletons in privileged structures constitutes a strong motivation to devise more effective arylation methods. Our design revolves around modulating the intrinsic nucleophilicity of aromatic amines and alcohols. The first approach involves the design of an electron-withdrawing activating group which could associate with the catalyst for reactivity enhancement and selectivity control. The resonance of arenes offers the unique mechanistic possibility to select between activating sites. C2-Azo- and nitroso-substituted naphthalenes undergo atroposelective ortho C- or N-arylation with (hetero)aromatic nucleophiles. For monocyclic benzenes, programmable charge localization leads to regioselective activation by catalytic control alone or aided by substrate design. For instance, selective addition to nitroso nitrogen enables successive annulation initiated by the amine to yield axially chiral N-arylbenzimidazoles. In a biomimetic manner, a finely tuned catalyst could direct a para-selective nucleophilic approach in the atroposelective arylation of azobenzenes. The second strategy employs electrophilic arene precursors for arylation which occurs via rearomatization with central-to-axial chirality transfer. This enabled the arylation of (imino)quinones with indoles to access phenylindole atropisomers. By adapting this chemistry with an additional oxidation event to liberate the carbonyl functionalities, aryl-o-naphthoquinone and aryl-p-quinone atropisomers were attained. Along with the development of new arylation strategies, deriving new axially chiral structures has been another consistent theme of our research program. The atroposelective functionalization of alkynes provides broad entry to atropisomeric alkenes. The monofunctionalization of alkynes through the interception of an electrophilic vinylidene-quinone-methide (VQM) intermediate with 2-naphthols yielded the new EBINOL scaffolds. By designing an internal directing group, the atroposelective dihalogenation of alkynes was realized using abundant alkali halides despite their weak nucleophilicities and poor solubilities. The atroposelective N-alkylation of alkenes was pursued to prepare multifunctionalized alkene atropisomers that could be converted into 2-arylpyrroles with chirality transfer. The synthesis of B-aryl-1,2-azaborines containing a C–B chiral axis was accomplished where the CPA catalyst effects the desymmetrization and defines the configuration of the distal C–B bond. Inspired by the axially chiral scaffold of allenes, we leveraged the developed arene activation strategy to achieve para-addition and dearomatization of judiciously designed azobenzenes, which led to structurally novel cyclohexadienylidene-based hydrazones. To complement these structures, axially chiral cyclohexadienyl oxime ethers were also attained through CPA-catalyzed condensation between hydroxylamines and spiro4.5trienones.
N‐arylcarbazole structures are important because of their prevalence in natural products and functional OLED materials. C−H amination of arenes has been widely recognized as the most efficient ...approach to access these structures. Conventional strategies involving transition‐metal catalysts suffer from confined substrate generality and the requirement of exogenous oxidants. Organocatalytic enantioselective C–N chiral axis construction remains elusive. Presented here is the first organocatalytic strategy for the synthesis of novel axially chiral N‐arylcarbazole frameworks by the assembly of azonaphthalenes and carbazoles. This reaction accommodates broad substrate scope and gives atropisomeric N‐arylcarbazoles in good yields with excellent enantiocontrol. This approach not only offers an alternative to metal‐catalyzed C–N cross‐coupling, but also brings about opportunities for the exploitation of structurally diverse N‐aryl atropisomers and OLED materials.
In the frame: Presented here is the first organocatalytic strategy for the synthesis of novel axially chiral N‐arylcarbazole frameworks by the assembly of azonaphthalenes and carbazoles. This reaction accommodates broad substrate scope and gives atropisomeric N‐arylcarbazoles in good yields with excellent enantiocontrol. This approach offers opportunities for the exploitation of structurally diverse N‐aryl atropisomers and OLED materials. CPA=chiral phosphoric acid.
With the increasing volume of high-resolution satellite images, image compression technology has become a research hotspot in the field of remote sensing image processing. However, existing remote ...sensing image compression methods, such as JPEG2000, fail to ensure high-ratio and high-fidelity compression. To address this issue, we utilize deep neural network to build a learned image compression model named HL-RSCompNet, specifically design for remote sensing images. This model considers both high-frequency and low-frequency features in remote sensing images. We use discrete wavelet transformation (DWT) to divide the image features into two components: high-frequency feature component and low-frequency feature component. In addition, we introduce a frequency domain encoding-decoding module with the goal of bolstering the model's capacity to represent both high-frequency and low-frequency features effectively. This approach allows the model to preserve more high-frequency information, thereby enhancing the overall compression performance of the learned image compression model. Extensive experimental and validation works are performed on four high-resolution remote sensing image datasets. The results indicate that our method outperforms existing traditional compression methods like JPEG2000 and even surpasses the performance of state-of-the-art learned image compression models. Our project is available at https://github.com/shao15xiang/HL-RSCompNet.
The well‐defined conformational properties of axially chiral compounds bring extraordinary values to an assortment of bioactive molecules, advanced materials, organocatalysts as well as chiral ...ligands in asymmetric transformations. The demonstrated usefulness and untapped potential of axially chiral structural motifs stimulate increasing efforts to develop novel and efficient approaches for their preparation. In this regard, the chiral phosphoric acids broadly used in asymmetric Brønsted acid catalysis have shown high relevance for atroposelective synthesis as well. Our strong interest in reaction chemistry of atropisomers has established a rewarding research programme in our group. The course of studies will be recounted in this Account, with discussion focused on the use of chiral phosphoric acids to catalyze construction of several key axially chiral structures such as BINAM, BINOL, NOBIN, arylquinones, SPINOL, arylpyrrole analogues and axially chiral alkenes.
What is the most favorite and original chemistry developed in your research group?
Organocatalytic asymmetric arene C—H functionalization.
What is the most important personality for scientific research?
Persistence, smart thinking.
What are your hobbies?
Playing basketball, playing card.
What's your favorite book(s)?
The Ordinary World by the famous Chinese writer Yao Lu.
Who influences you mostly in your life?
My parents and my supervisors Prof. Guofu Zhong and Carlos F. Barbas III.
How do you supervise your students?
I advise my students to work smartly and work hard.
The well‐defined conformational properties of axially chiral compounds bring extraordinary values to an assortment of bioactive molecules, advanced materials, organocatalysts as well as chiral ligands in asymmetric transformations. The demonstrated usefulness and untapped potential of axially chiral structural motifs stimulate increasing efforts to develop novel and efficient approaches for their preparation. In this regard, the chiral phosphoric acids broadly used in asymmetric Brønsted acid catalysis have shown high relevance for atroposelective synthesis as well. Our strong interest in reaction chemistry of atropisomers has established a rewarding research programme in our group. The course of studies will be recounted in this account, with discussion focused on the use of chiral phosphoric acids to catalyze construction of several key axially chiral structures such as BINAM, BINOL, NOBIN, arylquinones, SPINOL, arylpyrrole analogues and axially chiral alkenes.
Atropisomeric biaryl motifs are ubiquitous in chiral catalysts and ligands. Numerous efficient strategies have been developed for the synthesis of axially chiral biaryls. In contrast, the asymmetric ...construction of o-quinone-aryl atropisomers has yet to be realized. Inspired by the rapid progress of the chemistry of biaryls, here we present our initial investigations about the atroposelective construction of axially chiral arylquinones by a bifunctional chiral phosphoric acid-catalyzed asymmetric conjugate addition and central-to-axial chirality conversion. With o-naphthoquinone as both the electrophile and the oxidant, three types of arylation counterparts, namely 2-naphthylamines, 2-naphthols and indoles, are utilized to assemble a series of atropisomeric scaffolds in good yields and excellent enantioselectivities. This approach not only expands the axially chiral library but also offers a route to a class of potential, chiral biomimetic catalysts.
Presented here is a class of novel axially chiral aryl‐p‐quinones as platform molecules for the preparation of non‐C2 symmetric biaryldiols. Two sets of aryl‐p‐quinone frameworks were synthesized ...with remarkable enantiocontrol by means of chiral phosphoric acid catalyzed enantioselective arylation of p‐quinones by central‐to‐axial chirality conversion. These aryl‐p‐quinones were then used to access a wide spectrum of highly functionalized non‐C2 symmetric biaryldiols with excellent retention of the enantiopurity.
A class of atropisomeric aryl‐p‐quinones were efficiently assembled by means of chiral phosphoric acid catalyzed enantioselective arylation of p‐quinones through a central‐to‐axial chirality transfer process. This novel axially chiral framework served as a platform for diversity‐oriented synthesis of a wide range of highly functionalized non‐C2 symmetric biaryldiols with preservation of the chirality.
In recent years, visible light driven enantioselective chemical transformations have emerged as new additions to the toolkit of synthetic chemists to accomplish more efficient assembly of chiral ...molecules. Nonetheless, implementing precise stereocontrol on photoinduced intermolecular radical coupling process remains arduous. Recent studies unveil the underexplored competence of chiral phosphoric acid for this class of asymmetric photoredox reactions, endowed by its capability as a bifunctional H‐bonding catalyst for synchronous interaction with radical intermediate and substrate while channeling the cross‐coupling in a highly enantioselective manner. This paper highlights the recent advances, future outlook as well as the prospective challenges in this research area.
In recent years, visible light driven enantioselective chemical transformations have emerged as new additions to the toolkit of synthetic chemists to accomplish more efficient assembly of chiral molecules. Nonetheless, implementing precise stereocontrol on photoinduced intermolecular radical coupling process remains arduous. Recent studies unveil the underexplored competence of chiral phosphoric acid for this class of asymmetric photoredox reactions, endowed by its capability as a bifunctional H‐bonding catalyst for synchronous interaction with radical intermediate and substrate while channeling the cross‐coupling in a highly enantioselective manner. This paper highlights the recent advances, future outlook as well as the prospective challenges in this research area.
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