Catalytic asymmetric C-N cross-coupling towards boron-stereogenic 3-amino-BODIPYs

3-Amino boron dipyrromethenes (BODIPYs) are a versatile class of fluorophores widely utilized in live cell imaging, photodynamic therapy, and fluorescent materials science. Despite the growing demand for optically active BODIPYs, the synthesis of chiral 3-amino-BODIPYs, particularly the catalytic asymmetric version, remains a challenge. Herein, we report the synthesis of boron-stereogenic 3-amino-BODIPYs via a palladium-catalyzed desymmetric C-N cross-coupling of prochiral 3,5-dihalogen-BODIPYs. This approach features a broad substrate scope, excellent functional group tolerance, high efficiency, and remarkable enantioselectivities, under mild reaction conditions. Further stereospecific formation of chiral 3,5-diamino-BODIPYs, along with an investigation into the photophysical properties of the resulting optical BODIPYs are also explored. This asymmetric protocol not only enriches the chemical space of chiroptical BODIPY dyes but also contributes to the realm of chiral boron chemistry.

meso-Methyl Amination of BODIPYs by Regiospecific Cross Dehydrogenative Coupling via Direct C(sp3)-N(sp3) Bond Formation

Herein, we report a direct meso-methyl amination of BODIPY dyes by C(sp3)-N(sp3) bond formation using PIDA as an oxidant with a wide range of aliphatic secondary amines. This metal free cross dehydrogenative coupling reaction is regiospecific at the meso-methyl position of BODIPY in the presence of C1, C3, C5, and C7 methyl groups. Detailed nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry, and X-ray crystallographic studies were performed to establish the reaction mechanism and the regiospecificity of the reaction. Finally, the photophysical and electrochemical properties of the newly synthesized dyes were evaluated and rationalized.

A Practical and Modular Method for Direct C-H Functionalization of the BODIPY Core via Thianthrenium Salts

Direct structural modification of small-molecule fluorophores represents a straightforward and appealing strategy for accessing new fluorescent dyes with desired functionalities. We report herein a general and efficient visible-light-mediated method for the direct C-H functionalization of BODIPY, an important fluorescent chromophore, using readily accessible and bench-stable aryl and alkenylthianthrenium salts. This practical approach operates at room temperature with extraordinary site-selectivity, providing a step-economical means to construct various valuable aryl- and alkenyl-substituted BODIPY dyes. Remarkably, this protocol encompasses a broad substrate scope and excellent functional-group tolerance, and allows for the modular synthesis of sophisticated symmetrical and asymmetrical disubstituted BODIPYs by simply employing different combinations of thianthrenium salts. Moreover, the late-stage BODIPY modification of complex drug molecules further highlights the potential of this novel methodology in the synthesis of fluorophore-drug conjugates.

Visible-Light-Induced Direct Photoamination of BODIPY Dyes with Aqueous Ammonia

By taking advantage of their strong absorption ability, visible-light-induced direct photoamination of BODIPY dyes with aqueous ammonia was developed to give structurally diverse α-amino BODIPYs. The excited state of BODIPYs possessed higher electron affinity than the ground state and thus showed largely enhanced reactivity toward weak nucleophile of ammonia. Those α-amino BODIPYs are valuable synthetic intermediates and have been successfully demonstrated in several post-transformation reactions. The work indicates that photoreaction is an excellent alternative to conventional functionalization of this popular fluorophore.

Referential modification strategy based on phenolic hydroxyl-containing KSA luminogens for ER-targeting probe construction

The endoplasmic reticulum (ER) plays essential roles in various physiological processes and is intimately connected to kinds of diseases. The development of ER-targeting theranostic agents is highly demanded for precise treatments, however, the effective and referential strategies for the construction of ER-targeting probes are limited. Herein, we developed series of ER-targeting luminogens based on keto-salicylaldehyde azine (KSA) framework by introducing phenolic hydroxyl group, which present good theranostic performance with selective enrichment in ER. Under systematical structure modulation, the key role of phenolic hydroxyl group at K-terminal in ER-targeting was experimentally confirmed. Besides, the cyanobenzyl moiety at S-terminal can enhance the luminous efficiency and improve cellular uptake ability. Moreover, the generated reactive oxygen species (ROS) of these KSA derivatives can efficiently trigger ER stress to induce the apoptosis of cancer cells, resulting in the effective inhibition of tumor cells both in vitro and in vivo. Therefore, this feasible modification strategy of inserting phenolic hydroxyl group to common multi-aryl-based luminogens provides a reliable and referential approach for ER-targeting probe establishment.

Silver-mediated, direct phosphorylation of BODIPY dyes at the 3- or 3,5-positions with H-phosphonates

A direct and regioselective C-H/P-H cross-coupling of dialkyl phosphites, and diphenylphosphine oxide to easily available BODIPYs through an Ag-mediated radical addition, resulted in a series of new α-phosphorylated BODIPY fluorophores under mild conditions. Hydrolysis of the phosphonate gave the corresponding BODIPY phosphoric acid, which is soluble and fluorescent in water with a high quantum yield of 0.83.

An umpolung strategy for rapid access to thermally activated delayed fluorescence (TADF) materials based on phenazine

Herein, Ag(I)-promoted regioselective intramolecular radical nucleophilic addition/rearrangement of 2-aryl diazaboroles has been accomplished for the first time to construct phenazine structures. This protocol is an umpolung strategy based on the classical electrophilic mechanism, and therefore, a reversed regioselectivity was observed, which provides an opportunity to prepare sterically hindered phenazines. The resulting thermally activated delayed fluorescence (TADF) materials based on phenazine exhibit emission bands from green to red with high quantum yields and moderate fluorescence lifetimes as solid films.

Direct C–H alkoxylation of BODIPY dyes via cation radical accelerated oxidative nucleophilic hydrogen substitution: a new route to building blocks for functionalized BODIPYs

A convenient C–H alkoxylation reaction between BODIPY dyes and a variety of alcohols was developed via a cation radical accelerated oxidative nucleophilic hydrogen substitution.

Direct Amination of Aromatic C-H Bonds with Free Amines

Aromatic amines belong to a highly important class of organic compounds which are found in various natural products, functional materials, and pharmaceutical agents. Their prevalence has sparked continuing interest in the development of highly efficient and environmentally benign synthetic strategies for the construction of these compounds. Cross-dehydrogenative coupling reactions between two unmodified C(X)-H bonds have recently emerged as a versatile and powerful strategy for the fabrication of new C(X)-C(X) bonds. In this context, several procedures have been reported for the synthesis of aromatic amines through the direct amination of aromatic C-H bonds with free amines. This review highlights recent advances and progress in this appealing research arena, with special emphasis on the mechanistic features of the reactions.

Direct sulfonylation of BODIPY dyes with sodium sulfinates through oxidative radical hydrogen substitution at the α-position

A series of α-sulfonated BODIPYs were efficiently synthesized from sodium sulfinates via a radical process, and were demonstrated as new fluorescent probes for selective biothiol detection.

Highly regioselective α-formylation and α-acylation of BODIPY dyes via tandem cross-dehydrogenative coupling with in situ deprotection

A metal-free C-H formylation and acylation of BODIPY dyes using a variety of dioxolane derivatives as aldehyde equivalents is reported, providing a postfunctionalization method for controllable synthesis of BODIPYs with carbonyl groups at 3,5-positions via a radical process. The photophysical properties of resultant dyes from this efficient one-pot, chemo- and site-selective transformation have been studied.

β-AlkenylBODIPY Dyes: Regioselective Synthesis via Oxidative C-H Olefination, Photophysical Properties, and Bioimaging Studies

A series of 2-alkenyl- and 2,6-dialkenylboron dipyrromethene (BODIPY) derivatives were synthesized through Pd(II)-catalyzed regioselective and stereoselective oxidative C-H olefination in one step. The 2-alkenyl BODIPY derivative further reacted with various amines regioselectively at the 5-position through direct oxidative nucleophilic substitution. The photophysical properties of the 2-alkenyl- and 2,6-dialkenyl-substituted BODIPYs were investigated, which showed great potential in fluorescent bioimaging.

Transition-metal-free regioselective cross-coupling of BODIPYs with thiols

Transition-metal-free, regioselective C–H/S–H cross-couplings of BODIPYs with thiols provides structurally diverse thiolated BODIPYs via a radical pathway.

Silver(i)-mediated oxidative C(sp3)–H amination of ethers with azole derivatives under mild conditions

A silver(i)-mediated oxidative N–H/C(sp³)–H coupling of NH-azoles with ethers has been developed.

Development of BODIPY dyes with versatile functional groups at 3,5-positions from diacyl peroxides via Cu(ii)-catalyzed radical alkylation

A Cu(ii)-catalyzed, α-regioselective C–H alkylation of BODIPY with alkyl diacyl peroxides provides structurally diverse alkylated BODIPYs via a radical pathway.

Copper-catalyzed α-benzylation of BODIPYs via radical-triggered oxidative cross-coupling of two C–H bonds

An oxidative cross-dehydrogenative coupling of BODIPYs with toluene and it derivatives has been developed, allowing for the facile synthesis of a broad range of structurally diverse α-benzylated BODIPYs with high solid-state fluorescence.