The recent achievements of redox-neutral radical C–C cross-coupling enabled by visible-light

Xie, Jin; Jin, Hongming; Hashmi, A. Stephen K.

doi:10.1039/c7cs00339k

Cited by 449 publications

(147 citation statements)

References 50 publications

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“…Some cover the manipulation or installation of various functional groups [10–17], the synthesis of particular bonds (C–C or C–N etc . ) [18–21] or the synthesis of natural products or heterocycles [22–27]. Others provide an overview of catalysts and the transformations they enable [28–33].…”

Section: Introductionmentioning

confidence: 99%

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

Bogdos¹,

Pinard²,

Murphy³

2018

Beilstein J. Org. Chem.

105

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The focus of this review is to provide an overview of the field of organocatalysed photoredox chemistry relevant to synthetic medicinal chemistry. Photoredox transformations have been shown to enable key transformations that are important to the pharmaceutical industry. This type of chemistry has also demonstrated a high degree of sustainability, especially when organic dyes can be employed in place of often toxic and environmentally damaging transition metals. The sections are arranged according to the general class of the presented reactions and the value of these methods to medicinal chemistry is considered. An overview of the general characteristics of the photocatalysts as well as some electrochemical data is presented. In addition, the general reaction mechanisms for organocatalysed photoredox transformations are discussed and some individual mechanistic considerations are highlighted in the text when appropriate.

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Section: Introductionmentioning

confidence: 99%

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

Bogdos¹,

Pinard²,

Murphy³

2018

Beilstein J. Org. Chem.

105

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“…[16] On the basis of our recent mechanistic studies [5c] and the precedent literature, [5,19] we proposed a tentative mechanism as depicted in Figure 1. [20] In conclusion, we have developed neophyl rearrangement and reduction of distal carbon radicals based on the strategy of photoinduced iminyl radicalmediated CÀC bond cleavage. Next, the cyclic iminyl radical 1 a-A undergoes a facile ringopening CÀC bond fission to give highly reactive open-shell carbon radical 1 a-B.…”

mentioning

confidence: 99%

Photocatalytic Neophyl Rearrangement and Reduction of Distal Carbon Radicals by Iminyl Radical‐Mediated C−C Bond Cleavage

Wang

Yan

et al. 2018

Adv Synth Catal

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The control of selectivity in the reactions of the highly reactive open-shell carbon radicals is an attractive but often challenging task. Building on the strategy of photoinduced iminyl radicalmediated CÀC bond cleavage, we have developed photocatalytic neophyl rearrangement and reduction of distal carbon radicals under visible light irradiation of O-acyl oximes. This mild protocol tolerates a wide range of readily available O-acyl oximes, enabling facile synthesis of diversely substituted a,b-unsaturated nitriles and b-functionalized saturated nitriles in a highly selective manner.With the renaissance of the synthetic photochemistry, [1] the strategy of visible light-driven generation of nitrogen-centered radicals (NCRs) has found wide applications in NCR-based CÀN bond-forming reactions and CÀH bond activation/functionalization under mild conditions. [2,3] Remarkably, in this context, the photogeneration of cyclic iminyl radicals has also recently been successfully extended to CÀC bond cleavage, thus providing an enabling new tool for broadly applicable synthesis of alkyl nitriles. Inspired by the pioneering works from the Zard's group on iminyl radical-promoted cleavage of CÀC bond, [4] Zhou, [5a] Leonori, [5b] and our group [5c] independently disclosed that photoredox catalysis allowed facile generation of the corresponding iminyl radicals of type I from oxime ester or ether precursors through a SET reduction or SET oxidation processes. Subsequent CÀC single bond cleavage typically ensued to produce distal carbon radicals II, which could then trigger further chemical bond formations. [6] All of these methods lead to general synthesis of linear, saturated nitriles, when carbon radicals II were intercepted by various radical traps (Scheme 1A). Probably because of the issues concerning the control of chemoselectivity in the reactions of the highly reactive open-shell carbon radicals II, the otherwise desirable utility of such type of species in neophyl rearrangement [7] or direct reduction to assemble valuable a,b-unsaturated nitriles or b-functionalized saturated nitriles is largely unexplored.Due to the ubiquity of nitrile functionality in an important number of bioactive natural products and pharmaceuticals, [8] and broad utility in organic chemistry, [9] the synthesis of diversely functionalized Scheme 1. Photoinduced generation of cyclic iminyl radical and reaction design. SET = single electron transfer. LG = leaving group.

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“…Finally, SET from the reduced Ir II form of the photocatalyst to NCR 6 d‐B or sulfonyl radical 2 a‐A would regenerate the ground state Ir III photocatalyst, delivering benzenesulfonamide anion 6 d‐A and benzenesulfinate anion 2 a‐B . Notably, the entire reaction is a redox neutral process and does not require the addition of any external oxidant or reductant …”

Section: Methodsmentioning

confidence: 99%

“…[22] Thus, the reaction should proceed through the photogenerated N-radical-catalyzed processa s the major pathway.F inally,S ET from the reduced Ir II form of the photocatalyst to NCR 6d-B or sulfonyl radical 2a-A would regenerate the ground state Ir III photocatalyst, delivering benzenesulfonamide anion 6d-A and benzenesulfinatea nion 2a-B.N otably,t he entire reactioni sar edox neutralp rocess and does not require the addition of any external oxidanto rr eductant. [25] To demonstrate the utility of the developedc atalytic strategy,w ef urthera ttempted to extend the current methodf ar beyonda lkenea llylsulfonylation. Gratifyingly,o ur very preliminary results displayed that photogenerated NCR could also catalyze radicala lkynylsulfonylation of styrene 1a and 1-methyl-4-[(phenylethynyl)sulfonyl]benzene 13,t hough with moderate yield of product 14 (Scheme 5).…”

mentioning

confidence: 99%

Photogenerated Neutral Nitrogen Radical Catalyzed Bifunctionalization of Alkenes

Zhao

Chen

Zhou

et al. 2019

Chemistry A European J

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Alkene bifunctionalizations are powerful tools for the rapid construction of structurally complex and valuable scaffolds, and such reactions typically involve the use of transition‐metal catalysts or organocatalysts. Here, we report for the first time a photogenerated neutral nitrogen radical catalyzed intermolecular alkene bifunctionalization by using allyl sulfones as the source of both the carbon and the sulfone functionalities under mild conditions. The key to the success of this protocol involves the visible‐light‐mediated photocatalytic in situ generation of a nitrogen‐centered radical from the N‐(2‐acetylphenyl) benzenesulfonamide catalyst, and its activation of the allyl sulfones to generate reactive species. The preliminary control experiments supported the postulated mechanism.

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The recent achievements of redox-neutral radical C–C cross-coupling enabled by visible-light

Cited by 449 publications

References 50 publications

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

Photocatalytic Neophyl Rearrangement and Reduction of Distal Carbon Radicals by Iminyl Radical‐Mediated C−C Bond Cleavage

Photogenerated Neutral Nitrogen Radical Catalyzed Bifunctionalization of Alkenes

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