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Carboranes represent a class of compounds with increasing therapeutic potential. However, few general approaches to readily embed carboranes into small molecules, peptides, and proteins are available. We report a strategy based on palladium-mediated C–X (X = C, S, and N) bond formation for the installation of carborane-containing moieties onto small molecules and peptides. We demonstrate the ability of Pd-based reagents with appropriate ligands to overcome the high hydrophobicity of the carborane group and enable chemoselective conjugation of cysteine residues at room temperature in aqueous buffer. Accordingly, carboranes can be efficiently installed on proteins by employing a combination of a bis-sulfonated biarylphosphine-ligated Pd reagent in an aqueous histidine buffer. This method is successfully employed on nanobodies, a fully synthetic affibody, and the antibody therapeutics trastuzumab and cetuximab. The conjugates of the affibody Z(HER2) and the trastuzumab antibody retained binding to their target antigens. Conjugated proteins maintain their activity in cell-based functional assays in HER2-positive BT-474 cell lines. This approach enables the rapid incorporation of carborane moieties into small molecules, peptides, and proteins for further exploration in boron neutron capture therapy, which requires the targeted delivery of boron-dense groups.

We report a copper-catalyzed cycloaddition of hydrogen azide (hydrazoic acid, HN$_3$) with terminal alkynes to form 4-substituted-1H-1,2,3-triazoles in a sustainable manner. Hydrazoic acid was formed in situ from sodium azide under acidic conditions to react with terminal alkynes in a copper-catalyzed reaction. Using polydentate N-donor chelating ligands and mild organic acids, the reactions were realized to proceed at room temperature under aerobic conditions in a methanol–water mixture and with 5 mol % catalyst loadings to afford 4-substituted-1,2,3-triazoles in high yields. This method is amenable on a wide range of alkyne substrates, including unprotected peptides, showing diverse functional group tolerance. It is applicable for late-stage functionalization synthetic strategies, as demonstrated in the synthesis of the triazole analogue of losartan. The preparation of orthogonally protected azahistidine from Fmoc-L-propargylglycine was realized on a gram scale. The hazardous nature of hydrazoic acid has been diminished as it forms in situ in

Simultaneous introduction of two different palladium (pre)catalysts, one tuned to promote oxidative addition to (hetero)aryl bromide and another to activate terminal alkyne substrate, leads to productive Pd−Pd transmetalation, subsequent reductive elimination, and formation of disubstituted alkyne. This conceptually novel rational design of copper-free Sonogashira reaction enabled facile identification of the reaction conditions, suitable for the synthesis of alkyl, aryl, and heteroaryl substituted alkynes at room temperature with as low as 0.125 mol % total Pd loading.

We report a copper-catalyzed cycloaddition of hydrogen azide (hydrazoic acid, HN

The cationic palladium(II) complex 1 of pyridyl-mesoionic carbene ligand catalyzes Markovnikov-selective intermolecular hydroamination between anilines and terminal alkynes into the corresponding imines. The reaction proceeds at room temperature, in the absence of additives, with exquisite selectivity and diverse functional group tolerance. The key intrinsic feature of the catalyst is the pyridine wingtip confined to the proximity of the alkynophilic metal active site, which mimics the function of enzyme-like architectures by assisting entropically favored proton transfers.

Azocarboxamides occupy a special place among azo ligands owing to their versatility for metal coordination. Herein ruthenium complexes with two different azocarboxamide ligands that differ in the presence (or not) of a coordinating pyridyl heterocycle are presented. By making full use of the O,N(amide), N(azo), and N(pyridyl) coordinating sites, the first diruthenium complex that is bridged by an azo ligand containing two different binding pockets was obtained. Moreover, it was conclusively proven that, in the mononuclear complexes, oxidation at the ruthenium center leads to a complete change of coordination at the chelating binding pocket. The complexes were characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Additionally, the mechanism of the aforementioned redox-triggered change in the chelating binding pocket and the electronic structures of all the complexes were investigated by a combination of electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations. This is first instance in which a redox-driven change in the complete chelating binding pocket has been observed in a ruthenium complex as well as with azo-based ligands. These results thus show the potential of these versatile azocarboxamide ligands to act as redox-driven switches with possible relevance to electrocatalysis.

Ethyl 2-arylhydrazinecarboxylates can work as organocatalysts for Mitsunobu reactions because they provide ethyl 2-arylazocarboxylates through aerobic oxidation with a catalytic amount of iron phthalocyanine. First, ethyl 2-(3,4-dichlorophenyl)hydrazinecarboxylate has been identified as a potent catalyst, and the reactivity of the catalytic Mitsunobu reaction was improved through strict optimization of the reaction conditions. Investigation of the catalytic properties of ethyl 2-arylhydrazinecarboxylates and the corresponding azo forms led us to the discovery of a new catalyst, ethyl 2-(4-cyanophenyl)hydrazinecarboxylates, which expanded the scope of substrates. The mechanistic study of the Mitsunobu reaction with these new reagents strongly suggested the formation of betaine intermediates as in typical Mitsunobu reactions. The use of atmospheric oxygen as a sacrificial oxidative agent along with the iron catalyst is convenient and safe from the viewpoint of green chemistry. In addition, thermal analysis of the developed Mitsunobu reagents supports sufficient thermal stability compared with typical azo reagents such as diethyl azodicarboxylate (DEAD). The catalytic system realizes a substantial improvement of the Mitsunobu reaction and will be applicable to practical synthesis.

A novel bis(pyridyl-functionalized 1,2,3-triazol-5-ylidene)-palladium(II) complex [Pd(Py-tzNHC)2](2+) catalyses the copper-, amine-, phosphine-, and additive-free aerobic Sonogashira alkynylation of (hetero)aryl bromides in water as the only reaction solvent. The catalysis proceeds along two connected Pd-cycles with homogeneous bis-carbene Pd(0) and Pd(II) species, as demonstrated by electrospray ionization mass spectrometry.

A general protocol to independently access stereoisomerically pure β'-hydroxy-β-amino acid derivatives that is based on dibutylboron triflate-mediated aldol reaction of suitably protected β-amino acids bearing chiral oxazolidinone auxiliary is reported. The method smoothly afforded syn-aldol (α,β'-syn) products in pure form and excellent isolated yield. Both α,β-syn and α,β-anti isomers are readily accessible solely through the choice of the oxazolidinone chirality. This method allows for the preparation of stereoisomeric β'-hydroxy-β-amino acid derivatives that were previously unreported.

Ethyl 2-arylhydrazinecarboxylates can work as organocatalysts for Mitsunobu reactions because they provide ethyl 2-arylazocarboxylates through aerobic oxidation with a catalytic amount of iron phthalocyanine. First, ethyl 2-(3,4-dichlorophenyl)hydrazinecarboxylate has been identified as a potent catalyst, and the reactivity of the catalytic Mitsunobu reaction was improved through strict optimization of the reaction conditions. Investigation of the catalytic properties of ethyl 2-arylhydrazinecarboxylates and the corresponding azo forms led us to the discovery of a new catalyst, ethyl 2-(4-cyanophenyl)hydrazinecarboxylates, which expanded the scope of substrates. The mechanistic study of the Mitsunobu reaction with these new reagents strongly suggested the formation of betaine intermediates as in typical Mitsunobu reactions. The use of atmospheric oxygen as a sacrificial oxidative agent along with the iron catalyst is convenient and safe from the viewpoint of green chemistry. In addition, thermal analysis of the developed Mitsunobu reagents supports sufficient thermal stability compared with typical azo reagents such as diethyl azodicarboxylate (DEAD). The catalytic system realizes a substantial improvement of the Mitsunobu reaction and will be applicable to practical synthesis.

An investigation of the recently reported “fully catalytic Mitsunobu reaction” using catalytic amounts of a phosphine reagent and an azo reagent has shown that although benzyl 4-nitrobenzoate is formed under the fully catalytic conditions, the same result is obtained if the hydrazine catalyst is omitted, indicating that this is not a Mitsunobu reaction. In addition, when the reaction between (−)-ethyl lactate and 4-nitrobenzoic acid was carried out using the “fully catalytic” method, the corresponding ester was formed but in very low yield and with predominant retention of configuration. Unfortunately, the system catalytic in phosphine reagent is incompatible with that in the azo reagent.

A novel bis(pyridyl-functionalized 1,2,3-triazol-5-ylidene)-palladium(II) complex [Pd(Py-tzNHC)2]2+ catalyses the copper-, amine-, phosphine-, and additive-free aerobic Sonogashira alkynylation of (hetero)aryl bromides in water as the only reaction solvent. The catalysis proceeds along two connected Pd-cycles with homogeneous bis-carbene Pd0 and PdII species, as demonstrated by electrospray ionization mass spectrometry.

Azocarboxamide (azcH) has been combined for the first time with [Ru-Cym] to generate metal complexes with N,N- and N,O-coordination mode, [(Cym)Ru(azc)Cl] and [(Cym)Ru(azcH)Cl](+) [PF6 ](-). Geometric and electronic structures of the complexes are reported along with their in vitro activities against different tumour cell lines and preliminary results on solution chemistry. Compound [(Cym)Ru(azc)Cl] exhibited remarkable cytotoxic properties. It was cell-type specific and had comparable IC50 values towards both cancer cells and their drug-resistant subline. A tenfold increase in the sensitivity towards [(Cym)Ru(azc)Cl] was noted for the tumour cells with depleted intracellular glutathione (GSH) level, suggesting the essential role of GSH in cell response to this compound.

The application of activated carbon (Darco KB) for the acceleration and direction of the transformation of various 2H-pyran-2-ones with N-substituted maleimides toward isoindole derivatives through the reaction sequence cycloaddition/elimination/dehydrogenation is described. In this reaction, the catalyst mainly influences the dehydrogenation step, which is essential to avoid the formation of bicyclo[2.2.2]octenes as the other possible products. We found that the combination of Darco KB, as the metal-free catalyst, and decalin, as the solvent in a closed vessel, represents the most successful conditions. A comparison of the effect of various dehydrogenation catalysts and reaction conditions is also presented. In addition, we have proven that the aromatization occurs via a hydrogen transfer from the cyclohexadiene intermediate to the maleimide derivative (therefore producing succinimides). This transfer is facilitated by the active surface of the heterogeneous carbon-based catalyst.

The application of activated carbon (Darco KB) for the acceleration and direction of the transformation of various 2H-pyran-2-ones with N-substituted maleimides toward isoindole derivatives through the reaction sequence cycloaddition/elimination/dehydrogenation is described. In this reaction, the catalyst mainly influences the dehydrogenation step, which is essential to avoid the formation of bicyclo[2.2.2]octenes as the other possible products. We found that the combination of Darco KB, as the metal-free catalyst, and decalin, as the solvent in a closed vessel, represents the most successful conditions. A comparison of the effect of various dehydrogenation catalysts and reaction conditions is also presented. In addition, we have proven that the aromatization occurs via a hydrogen transfer from the cyclohexadiene intermediate to the maleimide derivative (therefore producing succinimides). This transfer is facilitated by the active surface of the heterogeneous carbon-based catalyst.