Iridium-Catalyzed Asymmetric Allylic Substitution with Sequential Boron Incorporation

An iridium-catalyzed asymmetric allylic substitution with sequential boron incorporation is reported. The reaction accommodates a wide range of substrates, affording chiral N,O-bidentate difluoroboron complexes in excellent yields with high enantioselectivities. Furthermore, decigram-scale reaction, synthetic transformations, as well as photophysical property investigations of the N,O-bidentate difluoroboron complexes are explored.

Metal catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides: structural diversity at the dipole partner

The 1,3-dipolar cycloaddition of azomethine ylides represents a versatile approach for synthesizing pyrrolidines, valuable structural motifs in synthetic and medicinal chemistry. However, most studies to date have relied predominantly on α-iminoesters as ylide precursors, thereby limiting the broader synthetic applications of this strategy. This feature article highlights alternative azomethine ylide precursors, beyond conventional α-iminoesters, which have facilitated the preparation of pyrrolidines with new subtitution patterns.

Catalytic Enantioselective Synthesis of Boron-Stereogenic and Axially Chiral BODIPYs via Rhodium(II)-Catalyzed C-H (Hetero) Arylation with Diazonaphthoquinones and Diazoindenines

The molecular engineering of boron dipyrromethenes (BODIPYs) has garnered widespread attention due to their structural diversity enabling tailored physicochemical properties for optimal applications. However, catalytic enantioselective synthesis of structurally diverse boron-stereogenic BODIPYs through intermolecular desymmetrization and BODIPYs with atroposelectivity remains elusive. Here, we showcase rhodium(II)-catalyzed site-specific C-H (hetero)arylations of prochiral BODIPYs and polysubstituted BODIPYs with diazonaphthoquinonesand diazoindenines, providing efficient pathways for the rapid assembly of versatile (hetero)arylated boron-stereogenic and axially chiral BODIPYs through long-range desymmetrization and axial rotational restriction modes. The synthetic application of the procedures has been emphasized by the efficient synthesis of BODIPY derivatives with various functions. Photophysical properties, bioimaging, and lipid droplet-specific targeting capability of tailored BODIPYs are also demonstrated, indicating their promising applications in biomedical research, medicinal chemistry, and material science.

Recent advances in the development of enantiopure BODIPYs and some related enantiomeric compounds

During the process of developing smart chiroptical luminophores, small chiral organic dyes have emerged as candidates of utmost importance. In this regard, the chiral variants of boron dipyrromethene (BODIPY) serve as suitable molecules owing to their excellent photophysical properties such as high fluorescence quantum yields, narrow emission bandwidths with high peak intensities, high photo and chemical stability, and higher molar extinction coefficients. Thus, the last decade observed an influx of research from various research groups for the induction of chirality in originally achiral BODIPY. Among these, the generation of chiral centers at various positions in BODIPY favored the synthetic accessibility towards this particular chiral pool, which in turn is found to be applicable in various areas like photodynamic therapy, bio-imaging, dye-sensitized solar cells, optoelectronics, fluorescent indicators, dye lasers, and chiral sensing. This review summarizes these various aspects of creating stereogenic centers at various positions, like α, β, meso, or at boron, in BODIPYs.

Enantioselective Addition of 1,3,5,7-Tetramethyl-BODIPYs to Isatins by Bifunctional Quinine-Based Squaramides

This work describes the development of the first enantioselective addition reaction between 1,3,5,7-tetramethyl-BODIPYs and isatin derivatives. The reaction utilizes bifunctional quinine/squaramide organocatalysts and affords nine novel chiral BODIPY dyes under mild conditions, with enantioselectivities reaching up to 60%. The synthesized BODIPY-oxindoles exhibit high fluorescence emissions, consistent with their parent BODIPYs, and display tunable colors. A representative example demonstrates a remarkably high quantum yield of 0.78 compared to fluorescein. Notably, the newly created carbon-stereocenter on the isatin skeleton induces detectable asymmetry in the electronically decoupled BODIPY chromophore. This is confirmed by the presence of Cotton effects in the visible region of the electronic circular dichroism (ECD) spectra. Density Functional Theory calculations suggested that the model oxindole 3aa adopts an (R) absolute stereochemical configuration, unveiling key interactions between the catalyst and substrates.

Real-Time Fluorescence Imaging of the Abscisic Acid Receptor Allows Nondestructive Visualization of Plant Stress

Environmental stress greatly decreases crop yield. The application of noninvasive techniques is one of the most practical and feasible ways of monitoring the health condition of plants under stress. However, it remains largely unsolved. A chemical fluorescent probe can be applied as a typical nondestructive method, but it has not been applied in living plants for stress detection to date. The abscisic acid (ABA) receptor plays a central role in conferring tolerance to environmental stresses and is an excellent target for developing fluorescent probes. Herein, we developed a fluorescence molecular imaging technology to monitor live plant stress by visualizing the protein expression level of the ABA receptor PYR1. A computer-aided designed indicator dye, flubactin, exhibited an 8-fold enhancement in fluorescence intensity upon interaction with PYR1. In vitro and in vivo experiments showed that flubactin is suitable to be used to detect salt stress in plants in real time. Moreover, the low toxicity of flubactin promotes its application in the future. Our work opens a new era for the nondestructive visualization of plant stress in vivo.

Studying the reactivity of alkyl substituted BODIPYs: first enantioselective addition of BODIPY to MBH carbonates

The first enantioselective addition of alkyl BODIPYs to Morita-Baylis-Hillman (MBH) carbonates is reported. This is the first reported enantioselective methodology using the methylene position of BODIPYs as a nucleophile. The reaction is efficiently catalyzed by cinchona alkaloids, achieving high enantioselectivities and total diastereoselectivity. The use of cinchona alkaloid pseudo enantiomers (chinine/cinchonine) allows us to obtain both pairs of enantiomers in similar yields and enantioselectivities, a common issue in this type of reaction. The photophysical study of these dyes (absorption and fluorescence) has been performed in order to determine their parameters and explore future possible application in bioimaging. In addition, electronic circular dichroism (ECD) studies supported by time-dependent density functional theory (TD-DFT) calculations were also performed.