- Engaging unactivated alkyl, alkenyl and aryl iodides in visible-light-mediated free radical reactions
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Radical reactions are a powerful class of chemical transformations. However, the formation of radical species to initiate these reactions has often required the use of stoichiometric amounts of toxic reagents, such as tributyltin hydride. Recently, the use of visible-light-mediated photoredox catalysis to generate radical species has become popular, but the scope of these radical precursors has been limited. Here, we describe the identification of reaction conditions under which photocatalysts such as fac-Ir(ppy) 3 can be utilized to form radicals from unactivated alkyl, alkenyl and aryl iodides. The generated radicals undergo reduction via hydrogen atom abstraction or reductive cyclization. The reaction protocol utilizes only inexpensive reagents, occurs under mild reaction conditions, and shows exceptional functional group tolerance. Reaction efficiency is maintained upon scale-up and decreased catalyst loading, and the reaction time can be significantly shortened when the reaction is performed in a flow reactor.
- Nguyen, John D.,D'Amato, Erica M.,Narayanam, Jagan M. R.,Stephenson, Corey R. J.
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- Photoredox catalysis on unactivated substrates with strongly reducing iridium photosensitizers
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Photoredox catalysis has emerged as a powerful strategy in synthetic organic chemistry, but substrates that are difficult to reduce either require complex reaction conditions or are not amenable at all to photoredox transformations. In this work, we show that strong bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands enable high-yielding photoredox transformations of challenging substrates with very simple reaction conditions that require only a single sacrificial reagent. Using blue or green visible-light activation we demonstrate a variety of reactions, which include hydrodehalogenation, cyclization, intramolecular radical addition, and prenylationviaradical-mediated pathways, with optimized conditions that only require the photocatalyst and a sacrificial reductant/hydrogen atom donor. Many of these reactions involve organobromide and organochloride substrates which in the past have had limited utility in photoredox catalysis. This work paves the way for the continued expansion of the substrate scope in photoredox catalysis.
- Shon, Jong-Hwa,Kim, Dooyoung,Rathnayake, Manjula D.,Sittel, Steven,Weaver, Jimmie,Teets, Thomas S.
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p. 4069 - 4078
(2021/04/06)
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- Dehydrogenation of N-Heterocycles by Superoxide Ion Generated through Single-Electron Transfer
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Nitrogen-containing heteroarene motifs are found in numerous pharmaceuticals, natural products, and synthetic materials. Although several elegant methods for synthesis of these compounds through dehydrogenation of the corresponding saturated heterocycles have been reported, some of the methods are hampered by long reaction times, harsh conditions, and the need for catalysts that are not readily available. This work reports a novel method for dehydrogenation of N-heterocycles. Specifically, O2.? generated in situ acts as the oxidant for N-heterocycle substrates that are susceptible to oxidation through a hydrogen atom transfer mechanism. This method provides a general, green route to N-heteroarenes.
- Huang, Yuan-Qiong,Song, Hong-Jian,Liu, Yu-Xiu,Wang, Qing-Min
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supporting information
p. 2065 - 2069
(2018/01/27)
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- Light-Mediated Reductive Debromination of Unactivated Alkyl and Aryl Bromides
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Cleavage of carbon-halogen bonds via either single-electron reduction or atom transfer is a powerful transformation in the construction of complex molecules. In particular, mild, selective hydrodehalogenations provide an excellent follow-up to the application of halogen atoms as directing groups or the utilization of atom transfer radical addition (ATRA) chemistry for the production of hydrocarbons. Here we combine the mechanistic properties of photoredox catalysis and silane-mediated atom transfer chemistry to accomplish the hydrodebromination of carbon-bromide bonds. The resulting method is performed under visible light irradiation in an open vessel and is capable of the efficient reduction of a variety of unactivated alkyl and aryl substrates.
- Devery, James J.,Nguyen, John D.,Dai, Chunhui,Stephenson, Corey R. J.
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p. 5962 - 5967
(2016/09/09)
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- Stable luminescent iridium(III) complexes with bis(N-heterocyclic carbene) ligands: Photo-stability, excited state properties, visible-light-driven radical cyclization and CO2 reduction, and cellular imaging
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A new class of cyclometalated Ir(iii) complexes supported by various bidentate C-deprotonated (C^N) and cis-chelating bis(N-heterocyclic carbene) (bis-NHC) ligands has been synthesized. These complexes display strong emission in deaerated solutions at roo
- Yang, Chen,Mehmood, Faisal,Lam, Tsz Lung,Chan, Sharon Lai-Fung,Wu, Yuan,Yeung, Chi-Shun,Guan, Xiangguo,Li, Kai,Chung, Clive Yik-Sham,Zhou, Cong-Ying,Zou, Taotao,Che, Chi-Ming
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p. 3123 - 3136
(2016/05/24)
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