Weakly coordinating, ketone-directed, regioselective monoallylation of arenes and indoles is reported using a stable and cost-effective high-valent cobalt(III)-catalyst to access several important molecular building blocks. The allylation proceeds smoothly with a variety of substrates in the presence of various electron-rich and -deficient substituents. The method was applied to the formal synthesis of an ancisheynine alkaloid, a highly conjugated azatetracene, and isochroman. The mechanistic study reveals that the allylation reaction follows a base-assisted intermolecular electrophilic substitution pathway.
Cost-effective and air-stable high-valent cobalt(III)-catalyzed weakly coordinating, ketonedirected regioselective mono-alkenylation of arenes and heteroarenes with alkenes is demonstrated. Various electron-rich and electron-deficient arenes are tolerated under the reaction conditions, providing E-alkenylated products exclusively. The tertbutyl-acrylates serve as an acrylic acid surrogate to provide cinnamic acid derivatives via direct CÀH alkenylation. A two-step synthesis of a g-PPAR antagonist, the synthesis of indanone, and the modification of divinylsulfone are reported as applications. The mechanistic details suggest a base-assisted intermolecular electrophilic substitution reaction pathway.
The presence of nitrogen atom in a wide variety of organic compounds called for the use of powerful CÀ H activation strategy in the CÀ N bond formation. Pentamethylcyclopentadienyl (Cp*) based, high-valent, group 9 transition-metal complexes have shown a great potential as catalysts in the CÀ H activation/functionalization over the years. This minireview summarizes recent progress made in the context of CÀ N bond formation via catalytic (sp 2)CÀ H activation with Cp*M(III) (M = Co, Rh and Ir) catalysts. A general plausible mechanism is briefly discussed at the beginning, and then results are arranged according to metal cobalt, rhodium and iridium, respectively.
A high-valent Ir(III)-catalyzed C−H bond functionalization is carried out for the first time on water for the synthesis of a biologically relevant chromone moiety. The C−H activation and annulation of salicylaldehydes with diazocompounds provided the desired chromones. The synthesis of C3-substitution-free chromones has also been demonstrated by a one-pot decarboxylation by employing tert-butyl diazoester. C3 and C5 C−H activations of the product chromone are also carried out under different conditions for further diversification.
The weakly coordinating, ketone‐directed, regioselective monoamidation of aromatic ketones, chalcone, carbazole, and benzophenones was achieved by employing high‐valent cobalt and rhodium catalysis to access numerous biologically important molecular building blocks. This amidation proceeded smoothly with a variety of ketones and several amidating partners. The application of the products in the synthesis of various heterocycles, including acridones, indoles, quinoline, quinolones, quinolinones, and quinazolines, was also explored. The total synthesis of acridone‐based alkaloids, namely, toddaliopsin A, toddaliopsin D, and arborinine, and the formal synthesis of acronycine and noracronycin were also accomplished by applying this method. A mechanistic study revealed this amidation reaction follows a base‐assisted intermolecular electrophilic substitution pathway.
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