A concise approach to indoles via oxidative C–H amination of 2-alkenylanilines using dioxygen as the sole oxidant

Abstract

An operationally simple and environmental friendly approach to indole derivatives from N-Ts-2-alkenylanilines has been achieved, which involves an oxidative intramolecular C–H amination by using molecular oxygen as sole oxidant.

Electrocatalytic Dehydrogenative Cyclization of 2-Vinylanilides for the Synthesis of Indoles

“…The development of efficient and sustainable synthetic methods to access indoles has been constantly pursued by organic chemists because of the prevalence of the indole moiety in bioactive compounds and natural products. , Among various methods for the synthesis of indoles, the oxidative cyclization of 2-vinylanilines provides regio-specific access to functionalized indoles from easily available materials. These reactions are commonly achieved using chemical oxidants with − or without − transition metal catalysts (Scheme A). The use of chemical oxidants in organic solvents not only pose significant safety and environmental concerns, but also produce stoichiometric waste products that may complicate product isolation and interfere with the desired transformation .…”

Iron-Promoted Construction of Indoles via Intramolecular Oxidative C–N Coupling of 2-Alkenylanilines Using Persulfate

“…uses molecular oxygen to transform N-tosylated 2-alkenylanilines and prepare N-Ts-indoles. 7 Although this reaction has been researched extensively, alkenylanilines that were not N-alkylated were not studied in most of these transformations, because of possible oxidative side reactions. 12 Thus, we wanted to explore the potential of direct heterocyclic indole formation from free 'NH' unprotected alkenylanilines using common oxidants.…”

“…4 The widespread applications of the indolic moiety prompted the development of more efficient procedures for its construction, especially using oxidant and/or transitionmetal catalytic methods, which remain an area of intensive research. [5][6][7] In this regard, transition-metal-catalyzed cyclization of 2-alkynyanilines for constructing new C-N/C-C bonds have been reported by groups of Cacchi, 8a de Lera, 8b and Liu, 8c using palladium-catalyzed reactions. The groups of Saá, 9a Xi, 9b Maiti, 9c and Li 9d have also reported the synthesis of 2-substituted indoles from anilines and olefins by using Rh(III) or Pd(II) catalyst.…”

Palladium-Catalyzed Sequential Vinylic C–H Arylation/Amination of 2-Vinylanilines with Aryl boronic Acids: Access to 2-Arylindoles

“…Palladium-catalyzed oxidative amination reactions have proven to be efficient and powerful, and many of them have been successfully applied in synthetic organic chemistry . Recently, a new class of alternative approaches based on nitrogen-centered radicals or cation addition to the vinyl to build the C–N bond have been developed by the research groups of Zheng, Chemler, Youn, and Deng, independently. Very recently, the intramolecular amination of 2-vinylanilines mediated by the electrophilic cation of main group elements, such as iodine and selenium, is described by Mũniz, Deng, Breder, and Zhao .…”