Distal radical migration strategy: an emerging synthetic means

Li, Weipeng; Xu, Wentao; Xie, Jin; Yu, Shouyun; Zhu, Chengjian

doi:10.1039/c7cs00507e

Cited by 293 publications

(95 citation statements)

References 50 publications

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“…Recently, visible light-mediated radical migration reactions have been recognized as a powerful method to trigger CAC and CAH bond functionalization [47][48][49]. Along these lines, Zhang group [50] developed an elegant method for the synthesis of baryl-c-ketophosphine oxides by using visible light-promoted 1,2aryl migration as the key step (Scheme 6).…”

Section: á-mentioning

confidence: 99%

Visible light-mediated C P bond formation reactions

2019

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Section: á-mentioning

confidence: 99%

Visible light-mediated C P bond formation reactions

2019

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“…LG = leaving group. [12,13] Initially, we chose 3,3-diphenyl-substituted O-acyl oxime 1 a as the model substrate, and examined the feasibility of the iminyl radical-mediated ring-opening/ neophyl rearrangement reaction (Table 1). [10] Recently, several photocatalytic cyanoalkylation methods have also been disclosed to provide attractive alternative access to various substituted alkyl nitriles.…”

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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“…48,54 Then, it adds to the terminal alkynyl carbon to generate vinyl radical I, 41,49 which cyclizes with the benzamide, followed by C-C bond scission to realize the first aryl migration. [55][56][57][58] The resulting acyl radical III undergoes 5-exo-trig cyclization with the intramolecular alkene part, giving α-boryl alkyl radical intermediate IV. After that, a second aryl migration occurs to give a stabilized radical intermediate VI.…”

Section: A Proposed Mechanism and Dft Calculationsmentioning

confidence: 99%

NHC-Boryl Radical Catalysis for Cycloisomerization With C–C Triple Bond Reorganization

et al. 2019

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Our present study unveils a new and efficient Nheterocyclic carbene (NHC)-boryl radical-catalyzed cycloisomerization of N-(2-ethynylaryl)arylamides. This catalytic process is triggered by the addition of an NHC-boryl radical to the alkynyl moiety, followed by a radical cascade comprising of an intramolecular cyclization, successive 1,5-and 1,2-aryl migrations, and the reorganization of a CC triple bond. Eventually, the catalytic cycle is achieved through a radical β-fragmentation reaction, from which the starting NHC-boryl radical is regenerated, and a structurally important quinolinone framework is assembled. A 13 C-labeling experiment was carried out to verify the CC triple bond reorganization, and the proposed catalytic pathway was supported further by density functional theory calculations. Our identification of NHC-boryl radical as a catalyst, as well as its mode of operation via radical addition/elimination mechanism, would stimulate the advancement of design of radical catalysis and the discovery of novel enantioselective radical-catalyzed processes.

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Distal radical migration strategy: an emerging synthetic means

Cited by 293 publications

References 50 publications

Visible light-mediated C P bond formation reactions

Visible light-mediated C P bond formation reactions

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

NHC-Boryl Radical Catalysis for Cycloisomerization With C–C Triple Bond Reorganization

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