Air-Stable Organoradical Boron Reagents

Both organic radicals and organoboron reagents have been broadly investigated, but the combination of them via direct C−H borylation as organic radical building blocks has never been achieved. Herein, a series of organoradical boron reagents, such as TTM-Bpin and TTM-BOH , were synthesized through the key step of C−H borylation of substrate TTM-H ((2,6-dichlorophenyl) bis(2,4,6-trichlorophenyl)methyl) radical for the first time. They are air stable enough to be stored in the solid state for several months under dark conditions, and fully investigated through single crystal analysis, EPR and DFT calculations. Furthermore, they can smoothly work in the standard Suzuki–Miyaura coupling (SMC) reaction with retention of the carbon radical center. Meanwhile, these radical species bearing different boron units display fluorescent character and are potentially applied for the collective synthesis of luminescent organic radicals, as well as other functionalized open-shell materials.     

A Convenient Synthesis of Triquinacene

We have recently reported the synthesis of a derivative of triquinacene (2,3-dihydrotriquinacen-2-one (14)⁴) from Thiele's acid (1). Although this new synthetic route is simple in concept, it suffers from a large number of chemical steps. We wish to communicate an important overall simplification of this synthetic scheme which makes readily available triquinacene (22) and several of its derivatives.     

Bis- and Tris-norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy Storage

Molecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy. In this work, phenyl- and naphthyl-linked bis- and tris-norbornadienes are presented as promising MOST systems with very high energy densities. The substrates were synthesized by Suzuki–Miyaura coupling reactions and their absorption properties and characteristic parameters for MOST applications were investigated. The norbornadiene derivatives showed absorption onsets of up to 386 nm and photoisomerization quantum yields of 56 % per photoisomerization event. The resulting quadricyclane products have half-lifes up to 14 d and very high energy densities of up to 734 kJ/kg. Overall, these norbornadienes fulfill necessary criteria for an optimal MOST system and are, therefore, a highly promising basis for the development of materials for efficient solar energy conversion and storage.     

Synthesis and photophysical studies of heteroaryl substituted-BODIPy derivatives for biological applications

Mono and di-heteroaryl-4,4′-difluoro-8-(aryl)-4-bora-3a,4a-diaza-s-indacene (BODIPy) (1–5) were synthesized using Suzuki–Miyaura couplings. Hetero aryl substitution on 3- or 3,5-positions caused large bathochromic shifts (up to ∼150 nm) in absorption (569–652 nm) and fluorescence maxima (586–679 nm) in comparison to classical BODIPy. Quantum yields were found to be as high as 0.65. Singlet oxygen production activities of these compounds were studied by monitoring the absorbance quenching of 1,3-diphenylisobenzofuran, on exposure to light (>600 nm). Cellular uptake of compound 4 was demonstrated using cervical cancer cells and fibroblast cell line and was confirmed by the images obtained using confocal microscope.     

The First Direct Synthesis of Corroles from Pyrrole

The solvent-free, catalyst-free condensation of pyrrole and aldehydes provides an extremely facile synthetic pathway to novel corroles [Eq. (1); Ar=C₆F₅, 2,6-F₂C₆H₃, 2,6-Cl₂C₆H₃]. The product containing pentafluorophenyl groups is an excellent precursor of other derivatives, including an ionic, water-soluble corrole.     

Coupling of 3,8-Dibromo-1,10-phenanthroline with 3,5-Diethynylheptyloxybenzene: A Suzuki/Miyaura Versus a Sonogashira Perspective

Abstract

We report a new application of the Suzuki-Miyaura reaction whereas two bifunctional reactants, 3,8-dibromo-1,10-phenanthroline and 3,5-diethynylheptyloxylbenzene (9), yield 3,8-bis(3-ethynyl-5-heptyloxyphenylethynyl)-1,10-phenanthroline (2) efficiently (74% yield) without polymerization. This was achieved by reacting a stoichiometric amount of 9 and (Me₃Si)₂NLi to obtain quantitatively the monoacetylide anion of 9 (10). The latter was activated with B-methoxy-9-BBN and reacted in analogy to the alkynyl copper complex of a Sonogashira route. However, in the Sonogashira reaction, the alkynyl copper complex is present in small equilibrium concentrations and polymerization takes place even when reagents are mixed slowly. Actually the Sonogashira route gave no desired product 2, as the latter polymerizes easily via homo-coupling in the presence of air and Cu(I).     

Convenient Method for the Reduction of the Double-Bond of Cyclic Vinylphosphine Oxides Using Borane

The electronpoor double-bond of cyclic vinylphosphine oxides (1, 3 and 4) is easily reduced by borane in a selective manner to give the corresponding saturated derivatives (2, 4 and 5, respectively) Under forcing conditions, change of the functionality may also take place.     

Synthesis of 3-hetarylpyrroles by Suzuki–Miyaura cross-coupling

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Preparing Pd catalysts based on urea ligand via electrospinning for Suzuki–Miyaura cross-coupling reactions

Pd-catalyzed Suzuki–Miyaura cross-coupling (SMC) reactions are important in chemistry. In this work, using electrospinning technology, we prepared a novel type of composite catalyst with ligand structures such as urea-Pd/PAN (polyacrylonitrile) and used them to catalyze SMC reactions in nontoxic systems and “green” conditions (air atmosphere, low temperature, and short reaction time). This method of preparing hybrid materials is simple and easy to operate. The higher catalytic activity of the catalysts is attributed to active centers with rich electrons transferred from ligands with unique structures, which can decrease the activation energy of the rate-determining step (oxidative addition). In addition, urea-Pd/PAN composite catalysts exhibit higher catalytic performance than those reduced by H₂ because of the smaller size of active species and the more-efficient oxidative addition to Pd⁰–ligand complexes compared to Pd⁰.     

Suzuki–Miyaura Cross‐Coupling of Unprotected Halopurine Nucleosides in Water—Influence of Catalyst and Cosolvent

Abstract

Reaction conditions for the Suzuki–Miyaura cross‐coupling of unprotected halopurine nucleosides with arylboronic acids in aqueous media were investigated. A series of arylated purine nucleosides was prepared in water without an organic cosolvent, using either Pd(PPh₃)₄ or Pd(OAc)₂/TPPTS as the catalyst.     

Diethylenetriamine-functionalized single-walled carbon nanotubes (SWCNTs) to immobilization palladium as a novel recyclable heterogeneous nanocatalyst for the Suzuki–Miyaura coupling reaction in aqueous media

Pd supported on diethylenetriamine (DETA) modified single-walled carbon nanotubes (SWCNT-DETA/Pd) hybrid materials were fabricated for the first time. The prepared heterogeneous catalyst was characterized by XRD, FTIR, SEM, TGA, and TEM. The catalytic activity of the prepared catalyst was investigated by employing the Suzuki–Miyaura coupling reaction as a model reaction. A series of biphenyl compounds were synthesized through the Suzuki–Miyaura reaction using SWCNT-DETA/Pd²⁺ as a catalyst. The yields of the products were in the range from 80% to 98%. The catalyst can be readily recovered and reused at least for seven consecutive cycles without significant loss of its catalytic activity.     

Alternative Synthesis of 5-(1H-Pyrazol-4-yl)-2-{6-[(2,2,6,6-tetramethylpiperidin-4-yl)oxy]pyridazin-3-yl}phenol

A scalable and environmentally benign route to the free base of branaplam, a small molecule splicing modulator, was identified and developed. This alternative approach circumvented the inherent risk of dioxin formation associated with ortho-halo phenol derivatives present in the previous route. A Friedel–Crafts approach provided a reliable access to the key intermediate, subsequently followed by a Suzuki–Miyaura cross-coupling. Multiple process aspects of the synthetic approach were evaluated, and a robust process for its large-scale synthesis was developed and successfully demonstrated.     

Temperature-Controlled Mechanochemistry Unlocks the Nickel-Catalyzed Suzuki–Miyaura-Type Coupling of Aryl Sulfamates at Different Scales

Several mechanochemically heated processes have been published in recent years. However, precise control over the mechanochemical catalysed coupling reactions remained elusive. A recent report from Leitch, Browne and co-workers demonstrated how a programmable jar heater manifold delivers an efficient methodology for the Suzuki–Miyaura-type cross coupling reaction of aryl sulfamates and aryl boronic acid species. This methodology can be readily upscaled 200-fold using twin-screw extrusion methodologies.     

Methyl β-(Benzotriazol-l-yl) vinyl Ketone: A New p-Acetylvinyl Cation Equivalent

A simple and efficient two-step approach to methyl β-(benzotriazol-1-yl)vinyl ketone 7 is described. The synthetic utility of compound 7 has been demonstrated by nucleophilic substitutions of the benzotriazolyl group with a range of nucleophiles. Thus, methyl β-(benzotriazol-1-yl)vinyl ketone provides a new β-acetylvinyl cation equivalent.     

Immobilization of palladium nanoparticles as a recyclable heterogeneous catalyst for the Suzuki–Miyaura coupling reaction

This work describes the synthesis of Pd nanoparticles that are stabilized on CaAl-layered double hydroxide functionalized with Tris (tris(hydroxymethyl)aminomethane). The synthesized catalyst is characterized by several different analyses and has been successfully applied to the Suzuki–Miyaura reaction.     

Design,Synthesis and Late-Stage Modification of Indane-Based Peptides via [2+2+2] Cyclotrimerization

Here, we prepared several dipeptides containing 2-aminoindane-2-carboxylic acid (Aic) and carried out further synthetic transformations. Synthesis and purification of modified peptides by using [2+2+2] cyclotrimerization is a challenging task. We are able to modify the unusual amino acids and peptide derivatives by late-stage incorporation of benzylhalo functionality. To incorporate benzylhalo moiety we used [2+2+2] cyclotrimerization in the presence of Mo(CO)₆. These halo derivatives are potential substrates for further modification by Sonogashira reaction, Suzuki–Miyaura cross-coupling, sultine formation, and the Diels–Alder reaction sequence.     

Convenient Preparation of Cycloalkenyl Boronic Acid Pinacol Esters

A practical method for the preparation of cycloalkenyl boronic acid pinacol esters is described. These important synthetic intermediates are typically made using more expensive methods like transition metal-catalyzed borylation of alkenyl halides or triflates. In this work, they are obtained from the simple corresponding cycloalkanones, which are subjected to Shapiro reaction conditions followed by trapping with a borate ester. The requisite products are obtained in very good to excellent yields, and the reactions can be scaled up to multigram amounts. By providing a simple alternative to common methods that make use of expensive transition-metal catalysts and formation of sensitive intermediates, this convenient method will be useful for the synthesis of ring-containing partners for Suzuki–Miyaura cross-coupling and other reactions employing boronic esters as substrates.     

Palladium on Carbon-Catalyzed Cross-Coupling of Aryl Halides with Potassium p-Tolyltrifluoroborate in Air

Palladium supported on carbon (Pd/C) has been shown to be an effective catalyst for the cross-coupling of potassium p-tolyltrifluoroborate with a variety of aryl bromides and iodides. Yields ranging from moderate to good were obtained using Pd/C in ethanol/water mixtures with potassium carbonate as base at 50 °C under an air atmosphere.     

Oxidation of 5,15-Dioxaporphyrin: Its Generality and Novelty as an Oxaporphyrin Analogue

5,15-Dioxaporphyrin ( DOP ) is a novel meso-oxaporphyrin analogue and exhibits unique 20π-antiaromaticity, unlike its mother congener of 18π-aromatic 5-oxaporphyrin, commonly known as its cationic iron complex called verdohem, which is a key intermediate of heme catabolism. To reveal its reactivities and properties as an oxaporphyrin analogue, the oxidation of tetra-β-arylated DOP ( DOP-Ar₄ ) was explored in this study. Stepwise oxidation from the 20π-electron neutral state was achieved, and the corresponding 19π-electron radical cation and 18π-electron dication were characterized. Further oxidation of the 18π-aromatic dication resulted in the formation of a ring-opened dipyrrindione product by hydrolysis. Considering a similar reaction of verdoheme to ring-opened biliverdin in the heme degradation in nature, the current result consolidates the ring-opening reactivity of oxaporphyrinium cation species.