Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 8 de 8
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nat Protoc ; 15(5): 1760-1774, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32296151

RESUMO

The direct cleavage of otherwise inert C-H bonds has emerged as a sustainable approach for organic synthesis; in contrast to other approaches, these reactions result in the formation of fewer undesired by-products and do not require pre-functionalization steps. In recent years, oxidative C-H/N-H alkyne annulations and C-H oxygenations were realized by 3d metals. Unfortunately, most of these reactions require stoichiometric amounts of often toxic chemical oxidants. This protocol provides a general method for cobaltaelectro-catalyzed C-H activations of benzamides. Here, anodic oxidation obviates the need for a chemical oxidant and uses 10-20% of a more environmentally benign, inexpensive catalyst. We outline a detailed and precise description of the designed electrolytic cell for metallaelectrocatalysis, including readily available electrode materials and electrode holders. The custom-made device is further compared with the commercially available and standardized ElectraSyn 2.0 electrochemistry kit. As example applications of this approach, we describe cobaltaelectro-catalyzed C-H activation protocols for the direct C-H oxygenation of benzamides and resource-economical synthesis of isoquinolones. The cobaltaelectrocatalysis setup and reaction take about 17 h, while an additional 5 h have to be anticipated for workup and chromatographic purification. The methods described herein feature broad functional group tolerance, operational simplicity, low waste-product formation and an overall exceptional level of resource economy.


Assuntos
Benzamidas/química , Técnicas de Química Sintética/métodos , Cobalto/química , Técnicas Eletroquímicas/métodos , Catálise , Oxirredução
2.
Angew Chem Int Ed Engl ; 59(32): 13451-13457, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32243685

RESUMO

Asymmetric pallada-electrocatalyzed C-H olefinations were achieved through the synergistic cooperation with transient directing groups. The electrochemical, atroposelective C-H activations were realized with high position-, diastereo-, and enantio-control under mild reaction conditions to obtain highly enantiomerically-enriched biaryls and fluorinated N-C axially chiral scaffolds. Our strategy provided expedient access to, among others, novel chiral BINOLs, dicarboxylic acids and helicenes of value to asymmetric catalysis. Mechanistic studies by experiments and computation provided key insights into the catalyst's mode of action.

3.
ChemSusChem ; 13(13): 3306-3356, 2020 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-32065843

RESUMO

Inexpensive cobalt-catalyzed oxidative C-H functionalization has emerged as a powerful tool for the construction of C-C and C-Het bonds, which offers unique potential for transformative applications to modern organic synthesis. In the early stage, these transformations typically required stoichiometric and toxic transition metals as sacrificial oxidants; thus, the formation of metal-containing waste was inevitable. In contrast, naturally abundant molecular O2 has more recently been successfully employed as a green oxidant in cobalt catalysis, thus considerably improving the sustainability of such transformations. Recently, a significant momentum was gained by the use of electricity as a sustainable and environmentally benign redox reagent in cobalt-catalyzed C-H functionalization, thereby preventing the consumption of cost-intensive chemicals while at the same time addressing the considerable safety hazards related to the use of molecular oxygen in combination with flammable organic solvents. Considering the unparalleled potential of the aforementioned approaches for sustainable green synthesis, this Review summarizes the recent progress in cobalt-catalyzed oxidative C-H activation until early 2020.

4.
Eur J Med Chem ; 179: 863-915, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31306817

RESUMO

Naphthoquinones are of key importance in organic synthesis and medicinal chemistry. In the last few years, various synthetic routes have been developed to prepare bioactive compounds derived or based on lapachones. In this sense, this review is mainly focused on the synthetic aspects and strategies used for the design of these compounds on the basis of their biological activities for the development of drugs against the neglected diseases leishmaniases and Chagas disease and also cancer. Three strategies used to develop bioactive quinones are discussed and categorized: (i) C-ring modification, (ii) redox centre modification and (iii) A-ring modification. Framed within these strategies for the development of naphthoquinoidal compounds against T. cruzi. Leishmania and cancer, reactions including copper-catalyzed azide-alkyne cycloaddition (click chemistry), palladium-catalysed cross couplings, C-H activation reactions, Ullmann couplings and heterocyclisations reported up to July 2019 will be discussed. The aim of derivatisation is the generation of novel molecules that can potentially inhibit cellular organelles/processes, generate reactive oxygen species and increase lipophilicity to enhance penetration through the plasma membrane. Modified lapachones have emerged as promising prototypes for the development of drugs against leishmaniases, Chagas disease and cancer.


Assuntos
Antineoplásicos/farmacologia , Antiprotozoários/farmacologia , Doença de Chagas/tratamento farmacológico , Doenças Negligenciadas/tratamento farmacológico , Neoplasias/tratamento farmacológico , Quinonas/farmacologia , Animais , Antineoplásicos/síntese química , Antineoplásicos/química , Antiprotozoários/síntese química , Antiprotozoários/química , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Humanos , Leishmania/efeitos dos fármacos , Neoplasias/patologia , Quinonas/síntese química , Quinonas/química , Trypanosoma cruzi/efeitos dos fármacos
5.
Angew Chem Int Ed Engl ; 58(37): 12803-12818, 2019 09 09.
Artigo em Inglês | MEDLINE | ID: mdl-31077524

RESUMO

Molecular syntheses largely rely on time- and labour-intensive prefunctionalization strategies. In contrast, C-H activation represents an increasingly powerful approach that avoids lengthy syntheses of prefunctionalized substrates, with great potential for drug discovery, the pharmaceutical industry, material sciences, and crop protection, among others. The enantioselective functionalization of omnipresent C-H bonds has emerged as a transformative tool for the step- and atom-economical generation of chiral molecular complexity. However, this rapidly growing research area remains dominated by noble transition metals, prominently featuring toxic palladium, iridium and rhodium catalysts. Indeed, despite significant achievements, the use of inexpensive and sustainable 3d metals in asymmetric C-H activations is still clearly in its infancy. Herein, we discuss the remarkable recent progress in enantioselective transformations via organometallic C-H activation by 3d base metals up to April 2019.

6.
Angew Chem Int Ed Engl ; 57(47): 15425-15429, 2018 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-30289577

RESUMO

The enantioselective cobalt(III)-catalyzed C-H alkylation was achieved through the design of a novel chiral acid. The cobalt(III)-catalyzed enantioselective C-H activation was characterized by high position-, regio- and enantio-control under exceedingly mild reaction conditions. Thereby, the robust cooperative cobalt(III) catalysis proved tolerant of valuable electrophilic functional groups, including hydroxyl, bromo, and iodo substituents. Mechanistic studies revealed a considerable additive effect on kinetics and on a negative non-linear-effect.

7.
Chemistry ; 23(50): 12145-12148, 2017 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-28675487

RESUMO

Sustainable, cobalt-catalyst enabled, synthetically significant C-F/C-H functionalizations were achieved with an ample substrate scope at an ambient temperature of 25 °C, thereby delivering perfluoroallylated heteroarenes. Detailed experimental and computational mechanistic studies on the C-F/C-H functionalizations provided strong support for a facile C-F cleavage.

8.
Chem Commun (Camb) ; 52(97): 14003-14006, 2016 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-27853761

RESUMO

Palladium catalyzed selective distal C-H activation with nitrile based templates has been of significant research interest in recent times. In this report, we disclose the distal C-H olefination of biphenyl systems with high regio- and stereo-selectivity and useful synthetic yields. The utility of this method has been demonstrated through its wide olefin scope, its operation at the gram scale and the easy removal/recovery of the directing group.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA