A new copper-catalyzed oxidative cyclization protocol was developed for the synthesis of 5,6-dihydropyrrolo[2,1-a]isoquinolines via a three-component reaction of tetrahydroisoquinolines with bromoketones and electron-deficient alkenes with air as a terminal oxidant. A variety of functional groups survived under the reaction conditions and the target products were obtained in good yields. This reaction features such advantages as eco-friendly reaction conditions, a simplified operation process and a broad substrate scope.
An efficient synthesis of diversified indolizine derivatives was developed via CuBr-catalyzed reaction of pyridines, methyl ketones and alkenoic acids under solvent-free conditions in oxygen atmosphere. This synthesis involves cascade processes of copper-catalyzed bromination of the methyl ketone, 1,3-dipolar cycloaddition of the pyridinium ylide with the alkenoic acid, followed by oxidative decarboxylation and dehydrogenative aromatization of the primary cycloadduct. By this protocol, a wide range of indoliznes with different substitution patterns were selectively prepared in one pot from simple substrates in good to excellent yields.
Aromatic heterocycles have been identified as effective directing groups (DGs) in C-H functionalization but can be retained as undesired bulky substituents in the final products. Herein, we report a Co(III)-catalyzed 1-aminoisoquinoline synthesis strategy based on oxadiazole-directed aromatic C-H coupling with alkynes and a subsequent redox-neutral C-N cyclization reaction. This labile N-O bond-based protocol has allowed the toleration of a broad range of functional groups.
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