Hidden Reactivity of Barbituric and Meldrum’s Acids: Atom-Efficient Free Radical C–O Coupling with N-Hydroxy Compounds

Synthesis ◽  
2021 ◽  
Author(s):  
Igor B. Krylov ◽  
Stanislav A. Paveliev ◽  
Alexander S. Budnikov ◽  
Oleg O. Segida ◽  
Valentina M. Merkulova ◽  
...  
Keyword(s):  
Free Radical ◽  
Hydrogen Atom ◽  
Hydroxamic Acids ◽  
Metal Free ◽  
Meldrum's Acids ◽  
Hydroxy Compounds ◽  
Coupling Partner

The reactivity of CH-acidic and structurally related enol-containing heterocycles towards N-oxyl radicals was disclosed. Traditionally, these substrates were considered as reactants for ionic transformations. Highly selective and efficient N-oxyl radical mediated C–O coupling of substituted barbituric or Meldrum’s acids with N-hydroxy compounds (N-hydroxyimides, hydroxamic acids, oximes, and N-hydroxybenzotriazole) was achieved using inexpensive manganese-containing salts as oxidants. Metal-free C–O coupling was demonstrated using diacetyliminoxyl as both the oxidant (hydrogen atom acceptor) and the coupling partner.

Transition-metal-free radical relay cyclization of vinyl azides with 1,4-dihydropyridines involving a 1,5-hydrogen-atom transfer: access to α-tetralone scaffolds

2020 ◽  
Vol 7 (22) ◽  
pp. 3638-3647
Author(s):  
Yangzhen Liao ◽  
Yu Ran ◽  
Guijun Liu ◽  
Peijun Liu ◽  
Xiaozu Liu
Keyword(s):  
Free Radical ◽  
Hydrogen Atom ◽  
Transition Metal ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Metal Free ◽  
Vinyl Azides

The remote C(sp3)–H functionalization enabled by a radical-mediated 1,5-hydrogen-atom transfer (HAT) process using vinyl azides and 1,4-dihydropyridines as precursors has been described.

Deaminative carbonylative thioesterification of activated alkylamines with thiophenols under transition-metal-free conditions

2021 ◽  
Author(s):  
Fengqian Zhao ◽  
Xiao-Feng Wu
Keyword(s):  
Free Radical ◽  
Transition Metal ◽  
Metal Free

A transition-metal-free radical carbonylation of activated alkylamines with thiophenols has been successfully developed. Various thioesters were selectively produced with moderate to good yields.

Metal-Free Photoredox-Catalyzed C–H/C–H Coupling of Arenes Enabled by Interrupted Pummerer Activation

2019 ◽  
Author(s):  
Miles Aukland ◽  
Mindaugas Šiaučiulis ◽  
Adam West ◽  
Gregory Perry ◽  
David Procter
Keyword(s):  
Natural Product ◽  
Selective Reduction ◽  
Cross Coupling ◽  
One Pot ◽  
Complex Molecules ◽  
Pummerer Reaction ◽  
Metal Free ◽  
Bond Forming ◽  
Coupling Partner ◽  
Bioactive Natural Product

<p>Aryl–aryl cross-coupling constitutes one of the most widely used procedures for the synthesis of high-value materials, ranging from pharmaceuticals to organic electronics and conducting polymers. The assembly of (hetero)biaryl scaffolds generally requires multiple steps; coupling partners must be functionalized before the key bond-forming event is considered. Thus, the development of selective C–H arylation processes in arenes, that side-step the need for prefunctionalized partners, is crucial for streamlining the construction of these key architectures. Here we report an expedient, one-pot assembly of (hetero)biaryl motifs using photocatalysis and two non-prefunctionalized arene partners. The approach is underpinned by the activation of a C–H bond in an arene coupling partner using the interrupted Pummerer reaction. A unique pairing of the organic photoredox catalyst and the intermediate dibenzothiophenium salts enables highly selective reduction in the presence of sensitive functionalities. The utility of the metal-free, one-pot strategy is exemplified by the synthesis of a bioactive natural product and the modification of complex molecules of societal importance.</p>

Recent advances in Minisci-type reactions and applications in organic synthesis

2020 ◽  
Vol 24 ◽  
Author(s):  
Wengui Wang ◽  
Shoufeng Wang
Keyword(s):  
Free Radical ◽  
Hydrogen Atom ◽  
Organic Synthesis ◽  
Radical Reactivity ◽  
Atom Loss ◽  
Radical Generation ◽  
In Situ Generation ◽  
Thermal Cleavage ◽  
Synthetic Chemist

Abstract:: Minisci-type reactions have become widely known as reactions that involve the addition of carbon-centered radicals to basic heteroarenes followed by formal hydrogen atom loss. While the originally developed protocols for radical generation remain in active use today, in recent years by a new array of radical generation strategies allow use of a wider variety of radical precursors that often operate under milder and more benign conditions. New transformations based on free radical reactivity are now available to a synthetic chemist looking to utilize a Minisci-type reaction. Radical-generation methods based on photoredox catalysis and electrochemistry, which utilize thermal cleavage or the in situ generation of reactive radical precursors, have become popular approaches. Our review will cover the remarkably literature that has appeared on this topic in recent 5 years, from 2015-01 to 2020-01, in an attempt to provide guidance to the synthetic chemist, on both the challenges that have been overcome and applications in organic synthesis.

A metal-free radical cascade reaction of phosphine oxides with 2-aryloxy phenylacetylenes to assemble diphosphonyl xanthene derivatives

2021 ◽  
Author(s):  
Tao Fan ◽  
Yan Liu ◽  
Caina Jiang ◽  
Yanli Xu ◽  
Yan-Yan Chen
Keyword(s):  
Free Radical ◽  
Transition Metal ◽  
Cascade Reaction ◽  
Phosphine Oxides ◽  
Metal Free ◽  
Mild Conditions ◽  
Xanthene Derivatives ◽  
Reaction Proceeds ◽  
Radical Cascade

A radical cascade reaction of 2-aryloxy phenylacetylene with phosphine oxides promoted by K2S2O8 was developed, provided diphosphonyl xanthenes as products. This reaction proceeds under transition metal-free and mild conditions with...

Metal-Free Cascade Methylation/Cyclization of N-Alkyl-N-methacryloylbenzamides with Dicumyl Peroxide

Synlett ◽  
2017 ◽  
Vol 29 (05) ◽  
pp. 617-620 ◽  
Author(s):  
Yan-Ning Niu ◽  
Xiao-Feng Xia ◽  
Yuan Yuan
Keyword(s):  
Free Radical ◽  
Dicumyl Peroxide ◽  
Metal Free ◽  
Wide Range ◽  
Radical Cascade ◽  
Convenient Access

A metal-free radical cascade methylation/cyclization of a wide range of N-alkyl-N-methacryloylbenzamides by using dicumyl peroxide as the methylating reagent provides a convenient access to a series of methylated isoquinoline-1,3-diones in moderate yields.

ChemInform Abstract: Metal-Free, Aerobic Dioxygenation of Alkenes Using Hydroxamic Acids.

ChemInform ◽  
2010 ◽  
Vol 41 (44) ◽  
pp. no-no
Author(s):  
Valerie A. Schmidt ◽  
Erik J. Alexanian
Keyword(s):  
Hydroxamic Acids ◽  
Metal Free

scholarly journals Synthesis of Polychloromethyl-Containing Indolines via Metal-Free Radical Arylpolychloromethylation of Unactivated Alkenes

2019 ◽  
Vol 39 (6) ◽  
pp. 1727 ◽  
Author(s):  
Wenlan Li ◽  
Yitong Sun ◽  
Yongchao Yao ◽  
Ying Xu ◽  
Peng Li ◽  
...  
Keyword(s):  
Free Radical ◽  
Metal Free
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