Photoredox Catalysis Enables Decarboxylative Cyclization with Hypervalent Iodine(III) Reagents: Access to 2,5-Disubstituted 1,3,4-Oxadiazoles

Li, Jian; Lu, Xue-Chen; Xu, Yilin; Wen, Jin-Xia; Hou, Guo-Quan; Liu, Li

doi:10.1021/acs.orglett.0c03663

Cited by 46 publications

(25 citation statements)

References 57 publications

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“…Taking into account the combined results of our mechanistic studies and previous reports, [10c,20] a plausible mechanism for this formal cycloaddition is illustrated in Figure 1. The reaction is initiated by the iron‐catalyzed decomposition of TBHP to form the tert ‐butoxy radical III , which undergoes hydrogen atom transfer (HAT) from TBHP to deliver the selective tert ‐butylperoxy radical IV .…”

Section: Methodssupporting

confidence: 70%

“…Recently, the Suero group, as well as the Alcarazo group reported the generation of a diazomethyl radical through the photoredox single electron transfer (SET) process (Scheme 1 b). [10] The diazo moiety could be transferred to either aromatic rings or hydrazones utilizing hypervalent I(III) [10a–d] or sulfonium ions [10e] as the leaving group. Since the electronic characteristics of the diazo group could be reversed from nucleophilic to electrophilic through the formation of the diazomethyl radical, [10a, 11] we considered whether electron‐neutral or even electron‐rich alkenes could be incorporated with the diazocarbon radical intermediate utilizing this umpolung strategy, [12] thereby providing a general methodology that would provide an alternative strategy for cycloaddition of alkenes that are unreactive towards dipolar cycloaddition.…”

Section: Methodsmentioning

confidence: 99%

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Generation of Diazomethyl Radicals by Hydrogen Atom Abstraction and Their Cycloaddition with Alkenes

Dong

Zheng

et al. 2021

Angew Chem Int Ed

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A general catalytic methodology for the synthesis of pyrazolines from α‐diazo compounds and conjugated alkenes is reported. The direct hydrogen atom transfer (HAT) process of α‐diazo compounds promoted by the tert‐butylperoxy radical generates electrophilic diazomethyl radicals, thereby reversing the reactivity of the carbon atom attached with the diazo group. The regiocontrolled addition of diazomethyl radicals to carbon‐carbon double bonds followed by intramolecular ring closure on the terminal diazo nitrogen and tautomerization affords a diverse set of pyrazolines in good yields with excellent regioselectivity. This strategy overcomes the limitations of electron‐deficient alkenes in traditional dipolar [3+2]‐cycloaddition of α‐diazo compounds with alkenes. Furthermore, the straightforward formation of the diazomethyl radicals provides umpolung reactivity, thus opening new opportunities for the versatile transformations of diazo compounds.

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Section: Methodssupporting

confidence: 70%

Section: Methodsmentioning

confidence: 99%

Generation of Diazomethyl Radicals by Hydrogen Atom Abstraction and Their Cycloaddition with Alkenes

Dong

Zheng

et al. 2021

Angew Chem Int Ed

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“…The reaction of α-oxocarboxylic acids 167 as precursors of acyl radical B with iodonium salt 166 in the presence of 4CzPN dye as a photocatalyst gives 2,5-disubstituted 1,3,4-oxadiazoles 168 in good yields (Scheme 53). 109 In the presented transformations, it is the diazo compound that quenches the luminescence of a photocatalyst generating reactive intermediates. Alternatively, a diazo reagent can react with active species formed in a photocatalytic cycle.…”

Section: Ylidesmentioning

confidence: 99%

Lightening Diazo Compounds?

Durka

Turkowska

Gryko

2021

ACS Sustainable Chem. Eng.

170

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The development of new sustainable reactions and protocols is essential to fulfill the growing demands of every branch of organic chemistry for greener synthetic methodologies. In this context, the use of visible light as the only source of energy is highly appealing. Since diazo compounds are valuable reagents in organic synthesis, their transformations realized in a sustainable manner are of interest. High reactivity and easy availability make them suitable for solar-driven transformations. Indeed, photochemical reactions of diazo compounds have recently proven a valuable alternative to transition metal catalysis. In this perspective, we highlight applications of these reagents under visible irradiation, particularly focusing on recent advancements. These include photochemical generation of carbenes and radicals which involve many relevant reactions, [2+1]-cycloadditions, X−H and C−H insertions, Wolff rearrangement, and more. Mechanistic aspects of these processes are briefly addressed to give readers a deeper understanding of rules underlying photoreactivity of diazo compounds. We conclude by emphasizing significant advancements and discussing challenges for future developments in the photochemistry of these valuable reagents.

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“…demonstrated that decarboxylatively generated acyl radicals can also be captured by diazomethyl radicals generated from hypervalent iodine species (Scheme 83). [360] Both radicals are generated in the presence of 4CzlPN as the photocatalyst, thus leading to a cascade synthesis of 1,3,4‐oxadiazole skeletons through a decarboxylation/cyclization sequence. Huo and co‐workers showcased that acyl radicals undergo addition to the N=N bonds of azobenzenes [361] .…”

Section: Decarboxylative C−pnictogen Bond Formationmentioning

confidence: 99%

Decarboxylation‐Initiated Intermolecular Carbon‐Heteroatom Bond Formation

Zeng¹,

Feceu

Sivendran

et al. 2021

Adv Synth Catal

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Carboxylic acids are among the most used feedstock chemicals due to their great structural diversity and easy handling. The use of carboxylic acids and their derivatives in decarboxylative couplings has proven to be a valuable tool for the construction of C−C and C‐heteroatom bonds. This synthetic strategy provides a complementary bond disconnection to traditional cross‐coupling methods. In this review, we provide a comprehensive overview of decarboxylation‐initiated intermolecular C‐heteroatom bond formation, outlining several main mechanistic concepts combined with early examples and highlighting the achievements made in the past decade until January 2021. In these reactions, carboxylic acids and their derivatives undergo initial decarboxylation and then react with other heteroatom electrophiles and nucleophiles, thus replacing the carboxylate group with a valuable and prevalent heteroatom functionality.

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Photoredox Catalysis Enables Decarboxylative Cyclization with Hypervalent Iodine(III) Reagents: Access to 2,5-Disubstituted 1,3,4-Oxadiazoles

Cited by 46 publications

References 57 publications

Generation of Diazomethyl Radicals by Hydrogen Atom Abstraction and Their Cycloaddition with Alkenes

Generation of Diazomethyl Radicals by Hydrogen Atom Abstraction and Their Cycloaddition with Alkenes

Lightening Diazo Compounds?

Decarboxylation‐Initiated Intermolecular Carbon‐Heteroatom Bond Formation

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