Radical Acylalkylation of 1,3-Enynes To Access Allenic Ketones via <i>N</i>-Heterocyclic Carbene Organocatalysis

Liu, Yanqing; Li, Qingzhu; Kou, Xin‐Xin; Zeng, Rong; Qi, Ting; Zhang, Xiang; Peng, Cheng; Han, Bo; Li, Jun‐Long

doi:10.1021/acs.joc.2c00037

Cited by 40 publications

(19 citation statements)

References 83 publications

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“…As disclosed in recent studies, they generally led to poor yields, including our stereoconvergent allenylation reaction (20-23) 50,[53][54][55] . Aliphatic aldehydes, substituted with diverse primary or secondary alkyl chains, participated efficiently in this 1,4functionalization of 1,3-enynes (24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39). However, moderate diastereoselectivities (5:1 dr to 10:1 dr) were generally observed in the cases of primary aliphatic aldehydes (24)(25)(26)(27)(28)(29), probably resulting from the reduced steric hindrance in comparison with secondary alkyl aldehydes (30)(31)(32)(33)(34)(35)(36)(37)(38)(39).…”

Section: Substrate Scopementioning

confidence: 99%

“…1a) 3 . On the other hand, the radical 1,4-functionalization of 1,3-enynes via allenyl or propargylic radicals has attracted much attention recently [20][21][22][23][24][25][26][27][28][29] , but only limited success has been achieved in their asymmetric versions. In 2020, the Bao and Zhang groups 30 , and Liu group 31 independently reported the elegant Cu-catalyzed enantioselective synthesis of chiral allenes via the radical 1,4-dicarbonization of 1,3-enynes.…”

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confidence: 99%

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Asymmetric 1,4-functionalization of 1,3-enynes via dual photoredox and chromium catalysis

et al. 2022

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The merger of photoredox and transition-metal catalysis has evolved as a robust platform in organic synthesis over the past decade. The stereoselective 1,4-functionalization of 1,3-enynes, a prevalent synthon in synthetic chemistry, could afford valuable chiral allene derivatives. However, tremendous efforts have been focused on the ionic reaction pathway. The radical-involved asymmetric 1,4-functionalization of 1,3-enynes remains a prominent challenge. Herein, we describe the asymmetric three-component 1,4-dialkylation of 1,3-enynes via dual photoredox and chromium catalysis to provide chiral allenols. This method features readily available starting materials, broad substrate scope, good functional group compatibility, high regioselectivity, and simultaneous control of axial and central chiralities. Mechanistic studies suggest that this reaction proceeds through a radical-involved redox-neutral pathway.

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Section: Substrate Scopementioning

confidence: 99%

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confidence: 99%

Asymmetric 1,4-functionalization of 1,3-enynes via dual photoredox and chromium catalysis

et al. 2022

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“…These methods show a wide scope with respect to the alkene acceptor, and styrenes, vinyl Along with alkenes, 1,3-enynes were also found to be potent radical acceptors that participate in analogous NHC-catalyzed three-component cross-couplings. In 2021, Du, 65 Huang, 66 and Li 67 independently demonstrated that perfluoroalkyl radicals regioselectively add to the terminal alkenyl moiety of the 1,3enyne to afford transient allenyl radicals, which can then be trapped by the cogenerated ketyl radicals to obtain tetrasubstituted allenyl ketones (Scheme 8).…”

Section: Set Oxidation Of Breslowmentioning

confidence: 99%

Radical NHC Catalysis

2022

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Radical/radical cross-coupling reactions represent an efficient and straightforward approach for the construction of chemical bonds and accordingly have drawn increasing attention over the past decades. In order to achieve synthetically useful transformations, a persistent radical should be coupled with a transient radical in accordance with the persistent radical effect (PRE). However, known transient radicals outnumber by far the known types of free persistent radicals, which limits the widespread application of the PRE, until today. Thus, the development of efficient cross-coupling reactions between transient radicals has been in focus, and meanwhile transition-metal catalysis has been successfully implemented to artificially prolong radical lifetimes, allowing their utilization in formal radical/radical cross-couplings. Complementary research in the field recently uncovered that organocatalytically generated NHC-derived ketyl radicals are a type of catalytically generated free persistent radicals. NHC-catalyzed radical transformations of aldehydes and carboxylic acid derivatives have enabled the disclosure of an ever-increasing number of interesting reactions, which are different from traditional NHC-catalyzed ionic processes, offering otherwise inaccessible activation modes. These discoveries have opened a door to NHC organocatalysis for the manipulation of radical reactions. Due to its obvious potential in synthetic organic chemistry, it is timely to provide a perspective on this emerging field.

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“…This transformation exhibited remarkable tolerance to diversified radical precursors, aliphatic and aromatic aldehydes and enyne substitution. Recently, Li's group developed the similar strategy with mainly 4‐aryl substituted 1,3‐enynes as the substrates [45] …”

Section: Organocatalyzed Reactions Involving Allenyl Radicalsmentioning

confidence: 99%

Allenyl Radicals in Organic Synthesis: Challenges and Recent Advances

Zhang

2022

Eur J Org Chem

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Allenyl radicals are rarely employed as intermediates for the synthesis of allenes probably owe to the lack of convenient methods for their generation and the high reactivity of short‐lived allenyl radicals. However, strategies take advantage of allenyl radicals are considered as a significant complement to reactions which couldn't proceed via an allenyl ionic pathway. As a result, several important methods have been developed in the past decades. Herein, this review is aimed to summarize the recent advance in reactions involving allenyl radicals by highlighting some outstanding challenges and confirming potential areas of improvement, which would offer an inspiration for future studies

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Radical Acylalkylation of 1,3-Enynes To Access Allenic Ketones via N-Heterocyclic Carbene Organocatalysis

Cited by 40 publications

References 83 publications

Asymmetric 1,4-functionalization of 1,3-enynes via dual photoredox and chromium catalysis

Asymmetric 1,4-functionalization of 1,3-enynes via dual photoredox and chromium catalysis

Radical NHC Catalysis

Allenyl Radicals in Organic Synthesis: Challenges and Recent Advances

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