Imine-palladacycles as phosphine-free precatalysts for low temperature Suzuki-Miyaura synthesis of nucleoside analogues in aqueous media

The synthesis and characterization of new water-soluble dinuclear palladacycles of the general formula [{Pd(R-C^N-SO3Na)(μ-AcO)}2] (R = H (1), OMe (2), Cl (3)) incorporating an ortho-metalated sodium 4-(N-benzylideneamino)benzenesulfonate moiety is reported. These complexes have been revealed to be excellent phosphine-free catalysts for the synthesis of functionalized nucleoside analogues involving a low-temperature Suzuki–Miyaura coupling of 5-iodo-2′-deoxyuridine with different arylboronic acids in neat water. The potential of 1–3 as synthetic precursors was also tested, and bridging acetates were cleaved by reaction with neutral PPh3, yielding the corresponding mononuclear derivatives [Pd(R-C^N-SO3Na)(AcO)(PPh3)] (R = H (4), MeO (5), Cl (6)). Analytical and spectroscopic techniques confirmed the proposed formulas and reactivities reported for complexes 1–6. Structural characterization by X-ray diffraction of single crystals grown from samples of 4 and 6 produced the unexpected but valuable crystallization-mediated compounds 4cm and 6cm that also supported the results presented here.This work has been partially supported by RTI2018-098233-B-C21 (MICINN) and 20790/PI/18 (Fundación SENECA CARM) grants. A.R.K would like to acknowledge SERB for EMR grant (EMR/2016/005439). Professor Gregorio Sánchez, who recently passed away, is gratefully acknowledged for his contribution to this work and his wise and continuous advise and suppor

Recyclable Supramolecular Ruthenium Catalyst for the Selective Aerobic Oxidation of Alcohols on Water: Application to Total Synthesis of Brittonin A

A supramolecule-based ruthenium catalyst has been developed for on-water aerobic oxidation of alcohols. The catalyst is synthesized by supporting ruthenium nanoparticles on cyclodextrin-modified graphene oxides (rGO@Ru-RMβ-CD) via a simultaneous one-pot reduction of ruthenium precursor and graphite oxide in water. The rGO@Ru-RMβ-CD was completely characterized by various techniques such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy to understand its morphology and structure. The catalyst showed promising efficiency with good selectivity for benzylic, propargylic, and aromatic alcohols under aqueous conditions. Sensitive functional groups such as −NH₂ and phenolic −OH were well tolerated under the reaction conditions and exclusively afforded the aldehydes in good to excellent yields with no side products. Moreover, the used catalyst was found to be easily recoverable and recyclable up to five times. Additionally, the developed oxidation methodology has been used as a key step for the total synthesis of natural product Brittonin A, including other functional group transformations such as Wittig olefination and reduction exclusively in water. Notably, these oxidation and reduction transformations could be carried out using the developed catalyst under aqueous conditions. This unique ability of the catalyst to switch between oxidation and reduction reactions simply by changing O₂ and H₂ atmospheres with a balloon assembly exemplifies its versatility. To the best of our knowledge this is a first report showing the total synthesis of a molecule completely on water

Phenothiazine-Based Cu(II)-Selective Fluorescent Sensor: GHK-Cu Sensing Applications

Sensing important metals in different environments is an important area and involves the development of a wide variety of metal-sensing materials. The employment of fluorescent sensors in metal sensing has been one of the most widely applied methodologies, and the identification of selective metal sensors is important. We herein report a phenothiazine-based Cu(II) fluorescent sensor that is highly selective to Cu(II) ions compared with other transition metal salts. The Lewis acidity of the Cu(II) salt certainly was found to be a factor for obtaining an enhanced sensing response in MeOH as the solvent, while a ratio of 1:1 was calculated to be the most optimum for getting the desired response

Cobalt(II)/<i>N</i>‑Hydroxyphthalimide-Catalyzed Cross-Dehydrogenative Coupling Reaction at Room Temperature under Aerobic Condition

This work reports a cobalt­(II)/<i>N</i>-hydroxyphthalimide (NHPI)-catalyzed cross-dehydrogenative oxidative coupling of <i>N</i>-aryl tetrahydroisoquinolines with various pro-nucleophiles, such as indoles, nitroalkanes, and trialkylphosphites, active methylene compounds, and other nucleophiles, such as cyanide (ethyl cyanoformate), at room temperature under aerobic conditions. The present protocol is operationally simple and can be carried out without photoirradiation and under peroxide-free conditions, even on a gram scale, to afford the products in good to excellent yields. On the basis of mass spectrometry and control experiments, a catalytic reaction pathway has been proposed

Active Palladium Colloids via Palladacycle Degradation as Efficient Catalysts for Oxidative Homocoupling and Cross-Coupling of Aryl Boronic Acids

Active palladium colloids formed upon degradation of a palladacyclic complex (Herrmann–Beller <b>1</b>) have been isolated for the first time and thoroughly characterized with techniques such as transmission electron microscopy (TEM), high-resolution TEM, X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure spectroscopy. The synthesized palladium colloids have been utilized as efficient catalysts for the oxidative homocoupling of aryl boronic acids. Cross-coupling of two different aryl boronic acids has also been made possible using these active palladium colloids. This is the first report of this kind of coupling between aryl boronic acids