Organocatalytic Asymmetric Construction and Application of Axially Chiral Spiro-bisindoles.

Spiro skeletons have emerged as a privileged class of chiral carriers across various research fields, including asymmetric catalysis and functional materials, due to their remarkable configurational rigidity. However, limited structural diversity of spiro frameworks significantly restricts the expansion of their applications. Here we present a new class of axially chiral spiro-bisindole frameworks and report their first enantioselective construction via a chiral phosphoric acid-catalyzed intramolecular dehydrative cyclization reaction.

Enantioselective Construction of Anthracenylidene-Based Axial Chirality by Asymmetric Heck Reaction.

Anthracenylidene is an intriguing structural unit with potential in various fields. The study presents a novel approach to introducing axial chirality into this all-carbon core skeleton through a remotely controlled desymmetrization strategy. A palladium-catalyzed enantioselective Heck arylation of exocyclic double bond of anthracene with two distinct substituents at the C10 position is harnessed to realize such a transformation.

Organocatalytic aromatization-promoted umpolung reaction of imines.

The umpolung functionalization of imines bears vast synthetic potential, but polarity inversion is less efficient compared with the carbonyl counterparts. Strong nucleophiles are often required to react with the N-electrophiles without catalytic and stereochemical control. Here we show an effective strategy to realize umpolung of imines promoted by organocatalytic aromatization.

Enantioselective Synthesis of Chiral Cyclobutenes Enabled by Brønsted Acid-Catalyzed Isomerization of BCBs.

Chiral cyclobutene units are commonly found in natural products and biologically active molecules. Transition-metal-catalysis has been extensively used in asymmetric synthesis of such structures, while organocatalytic approaches remain elusive. In this study, bicyclo[1.

Synthesis of Axially Chiral QUINAP Derivatives by Ketone-Catalyzed Enantioselective Oxidation.

QUINAPs have emerged as a pivotal class of axially chiral compounds with remarkable features in the stereoinduction of diverse enantioselective transformations. However, the confined substrate range and extravagant price still pose challenges, limiting their broader utilization. Herein, we describe the first atroposelective oxidation of an N atom using a chiral ketone catalyst, allowing the kinetic resolution of QUINAPOs to give both the unreacted substrates and their corresponding N-oxides with excellent enantioselectivity.

Organocatalytic Atroposelective Cross-Coupling of 1-Azonaphthalenes and 2-Naphthols.

Atroposelective cross-coupling is one of the most appealing routes to construct axially chiral binaphthyl molecules due to the modular and succinct nature. Although transition-metal-catalyzed cross-couplings offer reliable synthetic means, alternative reaction modes that could be applied to broader substrate range without their pre-functionalization is highly desirable. Herein we show that the application of chiral Brønsted acid catalyst as organocatalyst could accomplish cross-coupling of 1-azonaphthalenes and 2-naphthols with high efficiency, exclusive C4-selectivity as well as excellent enantioselectivity and functional group compatibility.

Modular enantioselective access to β-amino amides by Brønsted acid-catalysed multicomponent reactions.

β-Amino acids are structural motifs widely found in therapeutic natural products, novel biomimetic polymers and peptidomimetics. As a convergent method, the synthesis of stereoenriched β-amino amides through the asymmetric Mannich reaction requires specialized amide substrates or a metal catalyst for enolate formation. By a redesign of the Ugi reaction, a conceptually different solution to prepare chiral β-amino amides was established using ambiphilic ynamides as two-carbon synthons.

Enantioselective construction of triaryl-substituted all-carbon quaternary stereocenters organocatalytic arylation of oxindoles with azonaphthalenes.

Azonaphthalenes have been verified as a class of effective arylation reagents in a variety of asymmetric transformations. Here a highly efficient approach to construct triaryl-substituted all-carbon quaternary stereocenters through chiral phosphoric acid-catalyzed enantioselective arylation of 3-aryl-2-oxindoles with azonaphthalenes is disclosed. This chemistry is scalable and displays excellent functional group tolerance, furnishing a series of 3,3-disubstituted 2-oxindole derivatives in good yields with excellent enantiocontrol.

Acid Catalyzed Stereocontrolled Ferrier-Type Glycosylation Assisted by Perfluorinated Solvent.

Described herein is the first application of perfluorinated solvent in the stereoselective formation of -/-glycosidic linkages that occurs via a Ferrier rearrangement of acetylated glycals. In this system, the weak interactions between perfluoro--hexane and substrates could augment the reactivity and stereocontrol. The initiation of transformation requires only an extremely low loading of resin-H and the mild conditions enable the accommodation of a broad spectrum of glycal donors and acceptors.

Phosphoric Acid-Catalyzed Enantioselective Synthesis of Axially Chiral Anthrone-based Compounds.

Anthrones and analogues are structural cores shared by diverse pharmacologically active natural and synthetic compounds. The sp -rich nature imposes inherent obstruction to introduce stereogenic element onto the tricyclic aromatic backbone. In our pursuit to expand the chemical space of axial chirality, a novel type of axially chiral anthrone-derived skeleton was discovered.

Organocatalytic Enantioselective Synthesis of Axially Chiral Molecules: Development of Strategies and Skeletons.

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.

β-C-Glycosylation with 2-Oxindole Acceptors via Palladium-Catalyzed Decarboxylative Reactions.

This report describes a highly efficient β-selective -glycosylation of bicyclic galactals with 2-oxindoles through a palladium-catalyzed decarboxylative pathway. A variety of substrates representing both glycosyl donors and acceptors could be transformed in greater than 90% yields under mild reaction conditions. The decarboxylation intermediate of galactal could serve as an efficient base to deprotonate the enol tautomer of 2-oxindole and enhance its nucleophilicity.

Asymmetric Construction of an Aryl-Alkene Axis by Palladium-Catalyzed Suzuki-Miyaura Coupling Reaction.

The application of Suzuki-Miyaura coupling reaction to forge the atropisomeric biaryls has seen remarkable progress but exploration of this chemistry to directly forge chiral C(aryl)-C(alkene) axis is underdeveloped. The replacement of arene substrates by alkenes intensifies the challenges in terms of reactivity, configurational atropostability of product and selectivity control. By meticulous ligand design and fine-tuning of reaction parameters, we identified a highly active 3,3'-triphenylsilyl-substituted phosphite ligand to realize arene-alkene Suzuki-Miyaura coupling of hindered aryl halides and vinyl boronates under very mild conditions.

Towards more efficient ophthalmic disease classification and lesion location via convolution transformer.

Objective: A retina optical coherence tomography (OCT) image differs from a traditional image due to its significant speckle noise, irregularity, and inconspicuous features. A conventional deep learning architecture cannot effectively improve the classification accuracy, sensitivity, and specificity of OCT images, and noisy images are not conducive to further diagnosis.  This paper proposes a novel lesion-localization convolution transformer (LLCT) method, which combines both convolution and self-attention to classify ophthalmic diseases more accurately and localize the lesions in retina OCT images.

Direct arylation of N-heterocycles enabled by photoredox catalysis.

-Heterobiaryls are common skeletons found in biological molecules, pharmaceuticals and ligands. Herein, we document an efficient and redox-neutral photocatalytic system to obtain functionalized -heterobiaryls under mild conditions. Substrates bearing variegated functional groups are compatible with the developed photocatalytic conditions.

Facile synthesis of -aryl phenothiazines and phenoxazines Brønsted acid catalyzed C-H amination of arenes.

-Aryl phenothiazines and phenoxazines are of significant importance in various disciplines throughout academia and industry. The conventional synthetic strategy for the construction of these structures centers on the transition-metal-catalyzed cross-coupling of aryl halides with phenothiazines or phenoxazines. Here we present an organocatalytic approach to access -naphthyl phenothiazine and phenoxazine scaffolds through a straightforward C-H amination of arenes as enabled by an azo group.

Review and classification of AI-enabled COVID-19 CT imaging models based on computer vision tasks.

This article presents a systematic overview of artificial intelligence (AI) and computer vision strategies for diagnosing the coronavirus disease of 2019 (COVID-19) using computerized tomography (CT) medical images. We analyzed the previous review works and found that all of them ignored classifying and categorizing COVID-19 literature based on computer vision tasks, such as classification, segmentation, and detection. Most of the COVID-19 CT diagnosis methods comprehensively use segmentation and classification tasks.

Quality factor of partially coherent Airy beams in a turbulent atmosphere.

The quality factor of a partially coherent Airy beam in a turbulent atmosphere is investigated with the help of the extended Huygens-Fresnel integral formula and the Wigner distribution. From the numerical results, based on the analytical formula, we find that increasing the inner scale or decreasing the structure constant of the refractive index fluctuations of the turbulent atmosphere tends to decrease the quality factor of a partially coherent Airy beam in a turbulent atmosphere. Moreover, it is found that increasing the scale factor and wavelength or decreasing the coherent length of a partially coherent Airy beam can also be used to decrease the quality factor of a partially coherent Airy beam in a turbulent atmosphere.

Nitrosobenzene-Enabled Chiral Phosphoric Acid Catalyzed Enantioselective Construction of Atropisomeric N-Arylbenzimidazoles.

Described herein is an imidazole ring formation strategy for the synthesis of axially chiral N-arylbenzimidazoles by means of chiral phosphoric acid catalysis. Two sets of conditions were developed to transform two classes of 2-naphthylamine derivatives into structurally diverse N-arylbenzimidazole atropisomers with excellent chemo- and regioselectivity as well as high levels of enantiocontrol. It is worth reflecting on the unique roles played by the nitroso group in this domino reaction.

Chiral Phosphoric Acid-Catalyzed Remote Control of Axial Chirality at Boron-Carbon Bond.

The previously elusive catalytic enantioselective construction of axially chiral B-aryl-1,2-azaborines with a C-B stereogenic axis has been realized through a chiral phosphoric acid-catalyzed desymmetrization strategy reported herein. The electrophilic aromatic substitution reaction of 3,5-disubsituted phenols with diazodicarboxamides could afford these axially chiral structures in good efficiency with excellent enantiocontrol. The efficient long-range stereochemical control is achieved by multiple well-defined H-bonding interactions between chiral phosphoric acid and both substrates.

Organocatalyst-controlled site-selective arene C-H functionalization.

Over the past three decades, organocatalysis has emerged as a powerful catalysis platform and has gradually been incorporated into the routine synthetic toolbox to obtain chiral molecules. However, its application in the site- and enantioselective functionalization of inactive aryl C-H bonds remains in its infancy. Here, we present an organocatalyst-controlled para-selective arene C-H functionalization strategy that addresses this issue, which remains an enduring challenge in arene functionalization chemistry.

Electrochemical phenothiazination of naphthylamines and its application in photocatalysis.

N-Phenylphenothiazine as an inexpensive, highly reductive and oxygen tolerant organophotocatalyst has exhibited potential in various challenging photochemical transformations. Here we report a general and straightforward method to access structurally diverse N-phenylphenothiazine derivatives by means of a novel electrochemical tool. The introduction of a 2-naphthylamine moiety with an extended π-system and an amine group led to the variation of spectral characterization.

Copper-Catalyzed Synthesis of Axially Chiral Biaryls with Diaryliodonium Salts as Arylation Reagents.

NOBIN and BINAM derivatives harboring biaryl frameworks are recognized as a class of important atropisomers with versatile applications. Here, we present an efficient synthetic route to access such compounds through copper-catalyzed domino arylation of -arylhydroxylamines or -arylhydrazines with diaryliodonium salts and [3,3]-sigmatropic rearrangement. This reaction features mild conditions, good substrate compatibility, and excellent efficiency.

Asymmetric Pnictogen-Bonding Catalysis: Transfer Hydrogenation by a Chiral Antimony(V) Cation/Anion Pair.

Pnictogen-bonding catalysis based on σ-hole interactions has recently attracted the attention of synthetic chemists. As a proof-of-concept for asymmetric pnictogen-bonding catalysis, we report herein an enantioselective transfer hydrogenation of benzoxazines catalyzed by a novel chiral antimony cation/anion pair. The chiral pnictogen catalyst library could be rapidly accessed from triarylstibine with readily available mandelic acid analogues, and the catalyst displays remarkable efficiency and enantiocontrol potency even at 0.