RESUMEN

A novel Rh-catalyzed one-pot homo-coupling reaction of aryl Grignard reagents was achieved. The reaction with bromobenzenes having an electron-donating group or a halogen substituent gave the corresponding homo-coupling products in good yields, although the reaction using heterocyclic or aliphatic bromides scarcely proceeded. A Rh(III)-bis(aryl) complex, which might be formed from RhCl(PPh3)3 and the aryl Grignard reagents, plays an important role in giving the homo-coupling products in this reaction. Furthermore, we applied the reaction to the synthesis of a novel inhibitor for integrins which is critical for several diseases.

RESUMEN

Many biologically potent molecules have been identified to consist of benzo [b]azoles skeleton that are regarded to be the most important drug targets. Specifically, bis-benzo azoles have been the privileged conjugated structures due to their broad applications in environmental catalysis, and synthesis of various polymers, advanced materials, ligands, and natural products. Considering the significant features, different approaches have been attempted to synthesize such molecules via C-H activations by utilizing the transition metal complexes. In this study, we have developed facile and efficient Pd-based N-heterocyclic carbene (NHC) complexes, i.e., Pd-PEPPSI (Palladium-Pyridine Enhanced Pre-catalyst Preparation Stabilization and Initiation) catalysts that could successfully activate C-H bond and construct C-C bond between two 1,3-(benz)azoles via intermolecular oxidative homo-coupling reaction. The prepared Pd NHC catalysts were characterized by NMR and XPS. Pd NHCs concern about the special electronic and steric factors as the strong σ-donating and poor π-accepting properties of these nuclei renders great diversity in the field of transition metal catalysis as ancillary ligands and catalysts. Key factors of this methodology include low catalyst load, good substrate scope (even with sterically hindered substituted components), but no necessity of any extraneous ligands/oxidants and working at ambient reaction conditions with good to excellent yields of the products. Further, the targeted bis azole molecules have been characterized by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and cyclic voltammetric (CV) studies. The fluorescence and absorption spectra of a few of the synthesized compounds revealed that the electron-donating groups present on N-substituent dictate the absorption and emission bands.

Asunto(s)

RESUMEN

Electrochemical reactions are rapidly gaining attention today as a powerful and environmentally benign reaction processes for organic synthesis. We found that the electro-oxidation of palladium acetate afforded cationic palladium species and thus-generated cationic Pd species were efficient mediators for electro-oxidative coupling reactions. Homo-coupling of arylboronic acids and terminal alkynes proceeded efficiently to afford biaryls and butadiyne, respectively. Cross-coupling reactions between terminal alkynes and arylboronic acids were also achieved with the use of a Ag anode. As an advantage of electrochemical reactions, we developed a sequential reaction system switched between oxidative and neutral conditions by the on/off application of electricity, and several π-extended butadiynes were obtained in one-sequence by the system. Electrochemical intramolecular C-S coupling for the synthesis of thienoacene was also developed. The use of Bu4 NBr as a halogen mediator was essential for the reaction.

RESUMEN

The reactivity of aryl triflates in on-surface C-C coupling is reported. It is shown that the triflate group in aryl triflates enables regioselective homo coupling with preceding or concomitant hydrodetriflation on Cu(111). Three different symmetrical π-systems with two and three triflate functionalities were used as monomers leading to oligomeric conjugated π-systems. The cascade, comprising different intermediates at different reaction temperatures as observed for one of the molecules, proceeds via initial removal of the trifluoromethyl sulfonyl group to give an aryloxy radical which in turn is deoxygenated to the corresponding aryl radical. Thermodynamically driven regioselective 1,2-hydrogen atom transfer leads to a translocated aryl radical which in turn undergoes coupling. For a sterically more hindered bistriflate, where one ortho position was blocked, dehydrogenative coupling occurred at remote position with good regioselectivity. Starting materials, intermediates as well as products were analyzed by scanning tunneling microscopy. Structures and suggested mechanism were further supported by DFT calculations.

RESUMEN

A direct reductive homo-coupling of alkyl tosylates has been developed by employing a combination of nickel and nucleophilic cobalt catalysts. A single-electron-transfer-type oxidative addition is a pivotal process in the well-established nickel-catalyzed coupling of alkyl halides. However, the method cannot be applied to the homo-coupling of ubiquitous alkyl tosylates due to the high-lying σ*(C-O) orbital of the tosylates. This paper describes a Ni/Co-catalyzed protocol for the activation of alkyl tosylates on the construction of alkyl dimers under mild conditions.

Asunto(s)

RESUMEN

Diastereoselective radical coupling was achieved with chiral auxiliaries. The radicals were generated by anodic decarboxylation of five malonic acid derivatives. These were prepared from benzyl malonates and four menthol auxiliaries. Coelectrolyses with 3,3-dimethylbutanoic acid in methanol at platinum electrodes in an undivided cell afforded hetero-coupling products in 22-69% yield with a diastereoselectivity ranging from 5 to 65% de. Electrolyses without a coacid led to diastereomeric homo-coupling products in 21-50% yield with ratios of diastereomers being 1.17:2.00:0.81 to 7.03:2.00. The stereochemistry of the new stereogenic centers was confirmed by X-ray structure analysis and 13C NMR data.