Axially chiral indole‐based frameworks have been recognized as a class of important five‐membered heterobiaryls and developing catalytic asymmetric approaches for constructing these frameworks in an ...enantioselective manner is highly desirable. In recent years, synthetic chemists have paid much attention to this research field, and rapid developments have occurred. At this point, a range of axially chiral indole‐based scaffolds have been constructed via various catalytic asymmetric reactions based on different strategies. Thus, the catalytic asymmetric construction of axially chiral indole‐based frameworks has become an emerging area. This minireview summarizes the rapid advances in this field and gives some insights into future developments, which will help this research field to thrive.
Axially chiral indole‐based frameworks have been recognized as an important class of five‐membered heterobiaryls, and the catalytic asymmetric construction of this class of frameworks has become an emerging area. To give an in‐depth understanding of this area, this Minireview not only analyses its history and development trends, but also gives some insights into future developments based on the summarization of the rapid advances in this field.
The regio‐ and enantioselective (3+3) cycloaddition of nitrones with 2‐indolylmethanols was accomplished by the cooperative catalysis of hexafluoroisopropanol (HFIP) and chiral phosphoric acid (CPA). ...Using this approach, a series of indole‐fused six‐membered heterocycles were synthesized in high yields (up to 98 %), with excellent enantioselectivities (up to 96 % ee) and exclusive regiospecificity. This approach enabled not only the first organocatalytic asymmetric (3+3) cycloaddition of nitrones but also the first C3‐nucleophilic asymmetric (3+3) cycloaddition of 2‐indolylmethanols. More importantly, theoretical calculations elucidated the role of the cocatalyst HFIP in helping CPA control the reactivity and enantioselectivity of the reaction, demonstrating a new mode of cooperative catalysis.
The regio‐ and enantioselective (3+3) cycloaddition of nitrones with 2‐indolylmethanols has been established under the cooperative catalysis of hexafluoroisopropanol (HFIP) and chiral phosphoric acid (CPA). This approach not only realized the first organocatalytic asymmetric (3+3) cycloaddition of nitrones and the first C3‐nucleophilic asymmetric (3+3) cycloaddition of 2‐indolylmethanols but also revealed a new mode of cooperative catalysis.
A new class of axially chiral styrene‐based thiourea tertiary amine catalysts, which have unique characteristics such as an efficient synthetic route, multiple chiral elements, and multiple ...activating groups, has been rationally designed. These new chiral catalysts have proven to be efficient organocatalysts, enabling the chemo‐, diastereo‐, and enantioselective (2+4) cyclization of 2‐benzothiazolimines with homophthalic anhydrides in good yields (up to 96 %) with excellent stereoselectivities (all >95:5 dr, up to 98 % ee). More importantly, theoretical calculations elucidated the important role of an axially chiral styrene moiety in controlling both the reactivity and enantioselectivity. This work not only represents the first design of styrene‐based chiral thiourea tertiary amine catalysts and the first catalytic asymmetric (2+4) cyclization of 2‐benzothiazolimines, but also gives an in‐depth understanding of axially chiral styrene‐based organocatalysts.
A new class of axially chiral styrene‐based organocatalysts has been rationally designed. They enable the chemo‐, diastereo‐ and enantioselective (2+4) cyclization of 2‐benzothiazolimines. This work represents the first design of styrene‐based chiral thiourea tertiary amine catalysts and the first catalytic asymmetric (2+4) cyclization of 2‐benzothiazolimines, and it gives an in‐depth understanding of axially chiral styrene‐based organocatalysts.
With the rapid development of asymmetric catalysis, the demand for the enantioselective synthesis of complex and diverse molecules with different chiral elements is increasing. Owing to the unique ...features of atropisomerism, the catalytic asymmetric synthesis of atropisomers has attracted a considerable interest from the chemical science community. In particular, introducing additional chiral elements, such as carbon centered chirality, heteroatomic chirality, planar chirality, and helical chirality, into atropisomers provides an opportunity to incorporate new properties into axially chiral compounds, thus expanding the potential applications of atropisomers. Thus, it is important to perform catalytic asymmetric transformations to synthesize atropisomers bearing multiple chiral elements. In spite of challenges in such transformations, in recent years, chemists have devised powerful strategies under asymmetric organocatalysis or metal catalysis, synthesizing a wide range of enantioenriched atropisomers bearing multiple chiral elements. Therefore, the catalytic asymmetric synthesis of atropisomers bearing multiple chiral elements has become an emerging field. This review summarizes the rapid progress in this field and indicates challenges, thereby promoting this field to a new horizon.
The catalytic asymmetric synthesis of atropisomers bearing multiple chiral elements has recently become an emerging research field. Chemists have devised metal‐catalyzed or organocatalytic asymmetric reactions for accessing atropisomers with multiple chiral elements, such as those with center chirality, planar chirality, and helical chirality. This review summarizes the rapid developments in this field and indicated the remaining challenges.
Summary of main observation and conclusion
A new class of axially chiral aryl‐alkene‐indole frameworks have been designed, and the first catalytic asymmetric construction of such scaffolds has been ...established by the strategy of organocatalytic (Z/E)‐selective and enantioselective (4+3) cyclization of 3‐alkynyl‐2‐indolylmethanols with 2‐naphthols or phenols (all >95 : 5 E/Z, up to 98% yield, 97% ee). This reaction also represents the first catalytic asymmetric construction of axially chiral alkene‐heteroaryl scaffolds, which will add a new member to the atropisomeric family. This approach has not only confronted the great challenges in constructing axially chiral alkene‐heteroaryl scaffolds but also provided a powerful strategy for the enantioselective construction of axially chiral aryl‐alkene‐indole frameworks.
The first catalytic asymmetric construction of axially chiral aryl‐alkene‐indole scaffolds has been established by a (4+3) cyclization of 3‐alkynyl‐2‐indolylmethanols with 2‐naphthols or phenols.
Chiral nanostructures featuring the unique optical activity have attracted broad interests from scientists. The typical polarization rotation of transmitted light is usually wavelength dependent, ...namely the optical rotatory dispersion. However, its dynamic tunability and intriguing collaboration with other optical degrees of freedom, especially the highly desired spatial phase, remain elusive. Herein, a bi‐chiral liquid crystalline nanostructure is proposed to induce an effect called reflective optical rotatory dispersion. Thanks to the independent manipulation of opposite‐handed self‐assembled helices, spin‐decoupled geometric phases are induced simultaneously. These naturally unite multi‐dimensions of light and versatile stimuli‐responsiveness of soft matter. Dynamic holography driven by heat and electric field is demonstrated with a fast response. For polychromatic light, the hybrid multiplexed holographic painting is exhibited with fruitful tunable colors. This study extends the ingenious construction of soft chiral superstructures, presents an open‐ended strategy for on‐demand light control, and enlightens advanced applications of display, optical computing, and communication.
A bi‐chiral liquid crystalline nanostructure is proposed by customizing the transverse and longitudinal configuration of opposite‐handed cholesteric liquid crystals. Thanks to the reflective version of the common optical rotatory dispersion, the spin‐decoupled geometric phase modulation, and their multi‐stimuli responsiveness, the dynamic color‐tunable holography is realized desirably. This extremely extends the construction of soft chiral nanostructures and enlightens polychromatic light multiplexing.
In this work, we established catalytic asymmetric 4+1 cyclization of ortho‐quinone methides (o‐QMs) with 3‐chlorooxindoles and a catalytic asymmetric domino oxidation/4+1 cyclization reaction of ...2‐alkylphenols with 3‐chlorooxindoles, which constructed a spirooxindole‐based 2,3‐dihydrobenzofuran scaffold in good yield (up to 97%), with excellent diastereoselectivity (up to >95:5 dr) and high enantioselectivity (up to 99% ee). This work is not only the first highly enantioselective 4+1 cyclization of o‐QMs but has also realized the first catalytic asymmetric domino 4+1 cyclization of o‐QMs. In addition, both of the reactions provide efficient stereoselective methods for constructing spirooxindole‐based 2,3‐dihydrobenzofuran scaffolds with optical purity.
The ability to detect spatial and temporal microRNA (miRNA) distribution at the single-cell level is essential for understanding the biological roles of miRNAs and miRNA-associated gene regulatory ...networks. We report for the first time the development of a target-primed RCA (TPRCA) strategy for highly sensitive and selective in situ visualization of miRNA expression patterns at the single-cell level. This strategy uses a circular DNA as the probe for in situ hybridization (ISH) with the target miRNA molecules, and the free 3′ terminus of miRNA then initiates an in situ RCA reaction to generate a long tandem repeated sequence with thousands of complementary segments. After hybridization with fluorescent detection probes, target miRNA molecules can be visualized with ultrahigh sensitivity. Because the RCA reaction can only be initiated by the free 3′ end of target miRNA, the developed strategy offers the advantage over existing ISH methods in eliminating the interference from precursor miRNA or mRNA. This strategy is demonstrated to show high sensitivity and selectivity for the detection of miR-222 expression levels in human hepatoma SMMC-7721 cells and hepatocyte L02 cells. Moreover, the developed TPRCA-based ISH strategy is successfully applied to multiplexed detection using two-color fluorescent probes for two miRNAs that are differentially expressed in the two cell lines. The results reveal that the developed strategy may have great potential for in situ miRNA expression analysis for basic research and clinical diagnostics.
Sensor networks play an important role in structural health monitoring and tactile sensors. General sensor networks require different types and a large number of sensors. This article proposes a ...shape memory alloy (SMA) sensor interwoven network. Without the need for additional force or displacement sensors, the position of one external force acting on the sensor network can be estimated, and the magnitude of the force and the corresponding deformation of the sensor network can be determined, only by measuring the resistance of the SMA wires. This article not only proposes a theoretical analytical model to solve the force position and its magnitude, and even the entire deformation of the SMA sensor network, but also designs a sensor network and its test bench for loading experiments. The experimental results confirm the feasibility of the theoretical model. The SMA sensor interwoven network has important application value under the condition that it is not convenient to directly observe the position of the external force and monitor the force size, such as an intelligent self-sensing badminton racket at least.
![Catalytic Asymmetric [4+1] ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1615-4150/small "Catalytic Asymmetric [4+1] Cyclization of ortho‐Quinone Methides with 3‐Chlorooxindoles")
