Catalytic Dehydrogenative Cyclization of <i>o</i>‐Teraryls under pH‐Neutral and Oxidant‐Free Conditions

Tsukamoto, Tatsuhiro; Dong, Guangbin

doi:10.1002/ange.202004719

Cited by 8 publications

(2 citation statements)

References 63 publications

(22 reference statements)

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“…As for substrates containing benzofuran or a benzothiophene ring, the desired dehydrogenation products (P29, P30) were accompanied by fused aromatic compounds (P29′, P30′). The latter are probably produced from (Z)-P29 and (Z)-P30 via a 6π electrocyclization/SET/HAT sequence (a similar pathway has been reported by Dong for catalytic dehydrogenative cyclization of o-teraryls 36 ).…”

Section: Resultsmentioning

confidence: 99%

Site-Selective Acceptorless Dehydrogenation of Aliphatics Enabled by Organophotoredox/Cobalt Dual Catalysis

et al. 2021

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The value of catalytic dehydrogenation of aliphatics (CDA) in organic synthesis has remained largely underexplored. Known homogeneous CDA systems often require the use of sacrificial hydrogen acceptors (or oxidants), precious metal catalysts, and harsh reaction conditions, thus limiting most existing methods to dehydrogenation of non-or low-functionalized alkanes. Here we describe a visible-light-driven, dual-catalyst system consisting of inexpensive organophotoredox and base-metal catalysts for roomtemperature, acceptorless-CDA (Al-CDA). Initiated by photoexited 2-chloroanthraquinone, the process involves H atom transfer (HAT) of aliphatics to form alkyl radicals, which then react with cobaloxime to produce olefins and H 2 . This operationally simple method enables direct dehydrogenation of readily available chemical feedstocks to diversely functionalized olefins. For example, we demonstrate, for the first time, the oxidant-free desaturation of thioethers and amides to alkenyl sulfides and enamides, respectively. Moreover, the system's exceptional site selectivity and functional group tolerance are illustrated by late-stage dehydrogenation and synthesis of 14 biologically relevant molecules and pharmaceutical ingredients. Mechanistic studies have revealed a dual HAT process and provided insights into the origin of reactivity and site selectivity.

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Section: Resultsmentioning

confidence: 99%

Site-Selective Acceptorless Dehydrogenation of Aliphatics Enabled by Organophotoredox/Cobalt Dual Catalysis

et al. 2021

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“…[ 18 ] There are few examples of transition‐metal catalyzed dehydrogenation photocyclizations for the synthesis of fused heterocyclic aromatic hydrocarbons as well. [ 19‐20 ]…”

Section: Background and Originality Contentmentioning

confidence: 99%

Synthesis of2H‐benzo[g]furo/thieno/pyrrolo[2,3‐e]indazolesviaIntramolecular Dehydrogenation Photocyclization

et al. 2021

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A catalyst-, acid-and base-free, environmental-friendly method for synthesis of 2H-benzo[g]furo[2,3-e]indazoles, 2H-benzo[g]thieno[2,3-e]indazoles and 2H-benzo[g]pyrrolo[2,3-e]indazoles via UV light irradiation of 3-phenyl-4-(2-heteroaryl)pyrazoles (aryl = furanyl, thiophenyl and N-methylpyrrolyl) in EtOH/H 2 O at room temperature under argon atmosphere was described. Irradiation of 3-(2-hydroxyphenyl)-4-(2-heteroaryl)pyrazoles showed a high chemo-selectivity to obtain dehydrogenation product 2H-benzo[g]furo/ thieno/pyrrolo[2,3-e]indazols-10-ol. The mechanism of photocyclization was expounded through the process of 6π-electroncyclization, [1,5]-hydrogen shift, pyrazole tautomerism, 1,3-eneamine tautomerism and evolution of H 2 .

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Cobaloxime Photocatalysis for the Synthesis of Phosphorylated Heteroaromatics

Cheng

Chen

et al. 2022

Angewandte Chemie

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Herein, cobaloxime is used for the first time as a catalyst for the synthesis of phosphorylated heteroaromatics, which is an intriguing and versatile functional motif. With visible-light irradiation, cobaloxime not only oxidizes phosphine oxides to form phosphorus radicals (P-radicals) for a subsequent reaction with radical acceptor isocyanides or heteroaromatics, but also combines the radical intermediate with β-H elimination, thereby producing phosphorylated heteroaromatics with only H 2 or CH 4 as byproduct. Phosphine oxides with dialkyl, alkylaryl, and diaryl substituents could be directly transformed into phosphorylated phenanthridines, benzothiazoles, isoquinolines, and common heteroaromatics. This catalytic system features extremely mild conditions, broad substrate scope and good to excellent yields. Scale-up reaction and sunlight reaction show the great application potential in the green synthesis of important organophosphorus chemicals.

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Catalytic Dehydrogenative Cyclization of o‐Teraryls under pH‐Neutral and Oxidant‐Free Conditions

Cited by 8 publications

References 63 publications

Site-Selective Acceptorless Dehydrogenation of Aliphatics Enabled by Organophotoredox/Cobalt Dual Catalysis

Site-Selective Acceptorless Dehydrogenation of Aliphatics Enabled by Organophotoredox/Cobalt Dual Catalysis

Synthesis of2H‐benzo[g]furo/thieno/pyrrolo[2,3‐e]indazolesviaIntramolecular Dehydrogenation Photocyclization

Cobaloxime Photocatalysis for the Synthesis of Phosphorylated Heteroaromatics

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