TEMPO-Mediated Synthesis of Indolyl/Imidazo[1,2-<i>a</i>]pyridinyl-Substituted <i>para</i>-Quinone Methides from Butylated Hydroxytoluene

Nipate, Dhananjay S.; Sonam, -; Shinde, Vikki N.; Rangan, Krishnan; Kumar, Anil

doi:10.1021/acs.joc.1c02202

Cited by 8 publications

(7 citation statements)

References 42 publications

(15 reference statements)

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“…Unlike the previous works, the Ru‐catalyzed Matsuda‐Heck‐type arylation of p ‐QMs with aryl diazonium salts for the synthesis of symmetrical or unsymmetrical δ,δ′ ‐diaryl quinone methides was reported by Rong and Zhang et al [17a] . In addition, the TEMPO‐mediated cross‐dehydrogenative coupling (CDC) of butylated hydroxytoluene with indoles or imidazo[1,2‐a]pyridines was systematically investigated by Kumar et al [17b–c] . Furthermore, Yu, Zhang, Anand, Li, Tripathi and Lin et al .…”

Section: Methodsmentioning

confidence: 99%

Acid‐Catalyzed Regioselective Synthesis of α‐Diarylmethyl Substituted Phenols and para‐Quinone Methides in Water

Xiong

Shang

et al. 2022

Asian J Org Chem

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A facile and efficient method for the synthesis of αdiarylmethyl substituted phenols from para-quinone methides (p-QMs) with phenols has been developed by using phosphoric acid as the catalyst and water as the green solvent under mild conditions. In addition, when TEMPO was added as an additive for the reaction, the diaryl-substituted para-quinone methides could be generated as the target product. The reactions show high functional group tolerance, good to excellent yields and unique selectivity, and a broad range of α-diarylmethyl motif containing phenol(s) and quinones could be prepared through the divergent methods. Furthermore, a series of control experiments were performed to gain the insights of the plausible mechanisms. These protocols have a high atomic economy, and may have significant implications for the construction of C(sp 3 )À C(sp 2 ) bonds in organic synthesis.

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Section: Methodsmentioning

confidence: 99%

Acid‐Catalyzed Regioselective Synthesis of α‐Diarylmethyl Substituted Phenols and para‐Quinone Methides in Water

Xiong

Shang

et al. 2022

Asian J Org Chem

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“…1058 2,6-Di-tert-butyl-4-methylphenol (BHT) is transformed in the presence of TEMPO into quinone methide, which was used as an in situ-generated electrophile. 1059 Oxoammonium salts were also applied for oxidation of αand β-naphthols to give 1,2-naphthoquinones. 650,1060 By using a TEMPO-modified electrode for the in situ generation of TEMPO + , Osa and co-workers were able to homocouple naphthols and naphthol ethers.…”

Section: Oxidation Of Arenesmentioning

confidence: 99%

“…The resulting phenoxyl radical is trapped with a second equivalent of nitroxide 167 , and elimination of the N - tert -butyl benzamide finally delivers the targeted product . 2,6-Di- tert -butyl-4-methylphenol (BHT) is transformed in the presence of TEMPO into quinone methide, which was used as an in situ-generated electrophile …”

Section: Oxidation Reactionsmentioning

confidence: 99%

Organic Synthesis Using Nitroxides

Leifert

Studer

2023

Chem. Rev.

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Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R 1 R 2 N−O • . The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R 1 and R 2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R 1 R 2 N�O + ) or reduced to anions (R 1 R 2 N−O − ), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C−O bonds, allowing for the thermal generation of C radicals through reversible C−O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.

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“…[15] In recent years, para-quinone methides (p-QMs) have emerged as valuable synthons for the synthesis of diaryl-and triarylmethane derivatives. [16] The Calkylation of many N-heterocycles such as pyrroles/indoles, [17] imidazopyridines, [18] 2-alkylazaarenes, [19] 8-aminoquinolines, [20] indoline/tetrahydroisoquinolines [21] and other electron rich aromatic compounds [22] with p-QMs, through 1,6-conjugate addition reactions, have been well explored. In addition, the regioselective N-alkylation of 1,2,3-NH triazoles has been achieved through a 1,6-conjugate addition to p-QMs.…”

Section: Introductionmentioning

confidence: 99%

HBF₄‐Catalyzed 3,6‐Bis‐diarylmethylation of Carbazoles withpara‐Quinone Methides

2022

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In this article, we demonstrate an atom economical, practical, mild and selective HBF4‐catalyzed 1,6‐conjugate addition of carbazoles to para‐Quinone Methides (p‐QMs) to access 3,6‐bis‐diarylmethyl‐ and mono‐diarylmethyl carbazoles. This metal and additive free protocol provides convenient access to the substituted carbazole derivatives in moderate to excellent yields with a good functional group tolerance. It was found that a couple of 3,6‐disubstituted carbazoles showed interesting photophysical properties and, therefore, might potentially find some applications as host materials in OLEDs.

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TEMPO-Mediated Synthesis of Indolyl/Imidazo[1,2-a]pyridinyl-Substituted para-Quinone Methides from Butylated Hydroxytoluene

Cited by 8 publications

References 42 publications

Acid‐Catalyzed Regioselective Synthesis of α‐Diarylmethyl Substituted Phenols and para‐Quinone Methides in Water

Acid‐Catalyzed Regioselective Synthesis of α‐Diarylmethyl Substituted Phenols and para‐Quinone Methides in Water

Organic Synthesis Using Nitroxides

HBF₄‐Catalyzed 3,6‐Bis‐diarylmethylation of Carbazoles withpara‐Quinone Methides

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TEMPO-Mediated Synthesis of Indolyl/Imidazo[1,2-a]pyridinyl-Substituted para-Quinone Methides from Butylated Hydroxytoluene

Cited by 8 publications

References 42 publications

Acid‐Catalyzed Regioselective Synthesis of α‐Diarylmethyl Substituted Phenols and para‐Quinone Methides in Water

Acid‐Catalyzed Regioselective Synthesis of α‐Diarylmethyl Substituted Phenols and para‐Quinone Methides in Water

Organic Synthesis Using Nitroxides

HBF4‐Catalyzed 3,6‐Bis‐diarylmethylation of Carbazoles withpara‐Quinone Methides

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HBF₄‐Catalyzed 3,6‐Bis‐diarylmethylation of Carbazoles withpara‐Quinone Methides