Development of the suzuki-miyaura cross-coupling reaction: use of air-stable potassium alkynyltrifluoroborates in aryl alkynylations

Lanthanide-Based Probes for Imaging Detection of Enzyme Activities by NIR Luminescence, T1- and ParaCEST MRI

Applying a single molecular probe to monitor enzymatic activities in multiple, complementary imaging modalities is highly desirable to ascertain detection and to avoid the complexity associated with the use of agents of different chemical entities. We demonstrate here the versatility of lanthanide (Ln3+) complexes with respect to their optical and magnetic properties and their potential for enzymatic detection in NIR luminescence, CEST and T1 MR imaging, controlled by the nature of the Ln3+ ion, while using a unique chelator. Based on X-ray structural, photophysical, and solution NMR investigations of a family of Ln3+ DO3A-pyridine model complexes, we could rationalize the luminescence (Eu3+, Yb3+), CEST (Yb3+) and relaxation (Gd3+) properties and their variations between carbamate and amine derivatives. This allowed the design ofL n L G a l 5 ${{{\bf L n L}}_{{\bf G a l}}^{5}}$ probes which undergo enzyme-mediated changes detectable in NIR luminescence, CEST and T1-weighted MRI, respectively governed by variations in their absorption energy, in their exchanging proton pool and in their size, thus relaxation efficacy. We demonstrate that these properties can be exploited for the visualization of β-galactosidase activity in phantom samples by different imaging modalities: NIR optical imaging, CEST and T1-weighted MRI.

Azido-alkynylation of alkenes through radical-polar crossover

We report an azido-alkynylation of alkenes allowing a straightforward access to homopropargylic azides by combining hypervalent iodine reagents and alkynyl-trifluoroborate salts. The design of a photocatalytic redox-neutral radical polar crossover process was key to develop this transformation. A variety of homopropargylic azides possessing electron-rich and -poor aryls, heterocycles or ether substituents could be accessed in 34-84% yield. The products are synthetically useful building blocks that could be easily transformed into pyrroles or bioactive amines.

One-Pot Dual C-C Coupling Reaction via Site Selective Cascade Formation by PdII -Cryptate of an Amino-Ether Heteroditopic Macrobicycle

Selectivity of aryl iodo over ethynyl iodo toward the Suzuki cross coupling reaction is explored by utilizing a palladium complex of amino-ether heteroditopic macrobicycle. Subsequently, unreacted ethynyl iodide undergoes homocoupling reaction in the same catalytic atmosphere, thereby representing a cascade dual C-C coupling reaction. Furthermore, this approach is extended for novel one-pot synthesis of unsymmetrical 1,3-diynes.

Thiophene fused indenocorannulenes: synthesis, variable emission, and exceptional chiral configurational stability

Graph theory and isosteric replacement leads to the design and synthesis of (chiral) thiophene-fused indenocorannulenes with exceptional configurational stability and possible use as chiral catalysts, chiroptical materials, and sensors.

Double Porphyrin Cage Compounds

The synthesis and characterization of double porphyrin cage compounds are described. They consist of two porphyrins that are each attached to a diphenylglycoluril-based clip molecule via four ethyleneoxy spacers, and are linked together by a single alkyl chain using "click"-chemistry. Following a newly developed multistep synthesis procedure we report three of these double porphyrin cages, linked by spacers of different lengths, i.e. 3, 5, and 11 carbon atoms. The structures of the double porphyrin cages were fully characterized by NMR, which revealed that they consist of mixtures of two diastereoisomers. Their zinc derivatives are capable of forming sandwich-like complexes with the ditopic ligand 1,4-diazabicyclo[2,2,2]octane (dabco).

Ligand-Free Bioinspired Suzuki-Miyaura Coupling Reactions using Aryltrifluoroborates as Effective Partners in Deep Eutectic Solvents

Pd-catalyzed Suzuki-Miyaura cross-coupling between (hetero)aryl halides (Cl, Br, I) and versatile, moisture-stable mono- and bifunctional potassium aryltrifluoroborates proceeded efficiently and chemoselectively in air and under generally mild conditions; a catalyst loading as low as 1 mol % combined with Na₂ CO₃ as a base in choline chloride/glycerol (1:2) deep eutectic solvent (DES) was used as a sustainable and environmentally responsible medium. The catalyst, base, and DES were easily and successfully recycled up to six times with an E-factor as low as 8.74. Valuable biaryls and terphenyl derivatives were furnished in yields of up to 98 %; over 50 reactions were compared and discussed. The methodology was applied for the synthesis of the nonsteroidal anti-inflammatory drugs Felbinac and Diflunisal.

[Development of Novel Preparations for Nitrogen Heterocycles Based on Cascade Reactions]

　Nitrogen heterocycles are important skeletons in biologically active compounds such as medicines and natural alkaloids. However, in terms of the efficiency of the synthetic process, the many synthetic steps required to achieve the target compounds with complex architectures pose a significant problem. To overcome this challenge, novel approaches were developed to afford biologically active heterocycles, 1,2-diazepines, pyrroloisoquinolines, and pyrrolizidines utilizing cascade reactions that enable multiple bond formation in a one-pot process. This review discusses three one-pot reactions: 1) 1,2-diazepine synthesis from cyclobutenones and lithiodiazoesters via cascade 4π-8π electrocyclization; 2) synthesis of pyrroloisoquinolines from alkynylimino esters triggered by gold-catalyzed azomethine ylide formation; and 3) pyrrolizidine synthesis via three-component coupling reactions of iminoesters, acetylenes, and maleimides through the gold-catalyzed azomethine ylide generation/[3+2]-cycloaddition/enamine cyclization reaction.

Synthesis of Functionalized 1,3-Butadienes via Pd-Catalyzed Cross-Couplings of Substituted Allenic Esters in Water at Room Temperature

An environmentally responsible, mild method for the synthesis of functionalized 1,3-butadienes is presented. It utilizes allenic esters of varying substitution patterns, as well as a wide range of boron-based nucleophiles under palladium catalysis, generating sp-sp², sp²-sp², and sp²-sp³ bonds. Functional group tolerance measured via robustness screening, along with room temperature and aqueous reaction conditions highlight the methodology's breadth and potential utility in synthesis.

De novo synthesis of alkyne substituted tryptophans as chemical probes for protein profiling studies

De novo synthesis of alkynalted tryptophan moieties as chemical probes for protein profilling studies, via an unexpected synthesis of Michael acceptor 12 is reported. Friedel Craft's alkylation of 12 and alkyne substituted indoles gave alkynalated tryptophan moieties, which perform as chemical probe by incorporating into actively translating Escherichia coli cells, whereby the alkyne moiety enables multimodal analyses through click chemistry mediated attachment of reporting groups.

Palladium-Catalyzed Suzuki Cross-Coupling of 2-Halo-Deazapurines with Potassium Organotrifluoroborate Salts in the Regioselective Synthesis of Imidazo[4,5-b]pyridine Analogues

In this paper, we report the use of potassium organotrifluoroborate salts as nucleophilic organoboron reagents in the Suzuki cross-coupling reactions of 2-halo deazapurines. Regio-isomeric C-2-substituted imidazo[4,5-b]pyridine analogues were synthesized by employing this protocol in good to excellent yields. Whereas aryl and heteroaryl trifluoroborates reacted readily to give the coupled products in high yields, alkyltrifluoroborates were found to be less reactive. The utilization of tetrabutylammonium acetate was found to play a substantial role in enhancing the reaction rates of the cross-coupling process. Also, a comparative study was performed between boronic acids and potassium organotrifluoroborate salts.

Indium(iii)-catalyzed tandem synthesis of 2-alkynyl-3,3-dichloropyrrolidines and their conversion to 3-chloropyrroles

A convenient route to 2-alkynyl-3,3-dichloropyrrolidines was described by addition of terminal acetylenes to 2,2,4-trichloroaldimines using In(OTf)₃ as a catalyst. In the presence of a base these pyrrolidines were transformed into 3-chloropyrroles.

Synthesis, characterisation and reactions of phosphine-substituted alkynylboronates and alkynyltrifluoroborate salts

The synthesis and structural characterisation of phosphine-substituted alkynylboronates is reported. A P(III)-centred alkynylboronate (2) was prepared that showed little evidence for the conjugation of the P-lone pair to the boron via the alkyne π-system, as judged by X-ray crystallography studies of 2 and a related P(V) compound, 3. In addition, corresponding alkynyltrifluoroborate salts were prepared that showed improved stability by comparison to their boronic ester counterparts. These salts undergo Pd-catalysed cross-coupling reactions with aryl halides.

Synthesis and κ-opioid receptor activity of furan-substituted salvinorin A analogues

The neoclerodane diterpene salvinorin A, found in the leaves of Salvia divinorum, is a potent κ-opioid receptor agonist, making it an attractive scaffold for development into a treatment for substance abuse. Although several successful semisynthetic studies have been performed to elucidate structure-activity relationships, the lack of analogues with substitutions to the furan ring of salvinorin A has prevented a thorough understanding of its role in binding to the κ-opioid receptor. Herein we report the synthesis of several salvinorin A derivatives with modified furan rings. Evaluation of these compounds in a functional assay indicated that sterically less demanding substitutions are preferred, suggesting the furan ring is bound in a congested portion of the binding pocket. The most potent of the analogues successfully reduced drug-seeking behavior in an animal model of drug-relapse without producing the sedation observed with other κ-opioid agonists.

Copper-mediated radical trifluoromethylation of unsaturated potassium organotrifluoroborates

Copper-mediated trifluoromethylation of unsaturated organotrifluoroborates with the Langlois reagent (NaSO2CF3) and TBHP allows the introduction of trifluoromethyl groups into a variety of organic substructures. The reactions are easy to set up, the conditions are mild and general, and the process provides access to trifluoromethylated alkynes, alkenes, arenes, and heteroarenes in fair to good yields.

An improved route to 19-substituted geldanamycins as novel Hsp90 inhibitors--potential therapeutics in cancer and neurodegeneration

19-Substituted geldanamycin derivatives are efficient Hsp90 inhibitors, without the toxicity associated with the other benzoquinone ansamycins, thus giving them potential for use as molecular therapeutics in cancer and neurodegeneration. Here a new method of synthesising these important compounds is reported, eliminating the need for toxic metals and metalloids.

Microwave-enhanced cross-coupling reactions involving alkynyltrifluoroborates with aryl bromides

Palladium-catalyzed alkynylation has emerged as one of the most reliable methods for the synthesis of alkynes which are often used in natural product syntheses and material science. An efficient method for coupling alkynyltrifluoroborates with various aryl bromides in the presence of a palladium catalyst has been developed using microwave irradiation. The microwave reactions are rapid and efficient.

Aromatic cations from oxidative carbon-hydrogen bond cleavage in bimolecular carbon-carbon bond forming reactions

Chromenes and isochromenes react quickly with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form persistent aromatic oxocarbenium ions through oxidative carbon-hydrogen cleavage. This process is tolerant of electron-donating and electron-withdrawing groups on the benzene ring and additional substitution on the pyran ring. A variety of nucleophiles can be added to these cations to generate a diverse set of structures.

Synthesis and reactivity of solid-supported organotrifluoroborates in Suzuki cross-coupling

Solid-supported organotrifluoroborates were prepared in high yields by ion exchange with Amberlyst resins. The reactivity of solid supported aryltrifluoroborates was evaluated in Suzuki-Miyaura couplings with numerous aryl bromide partners. Electron-rich and -poor substituents were tolerated on both substrates, providing yields up to 90%. Examples of alkyl-, alkenyl-, alkynyl-, and heteroaryltrifluoborates were also successfully cross-coupled to aryl halides.