Borylative Heterocyclization without Air-Free Techniques

Gao, Chao; Nakao, Shuichi; Blum, Suzanne A.

doi:10.1021/acs.joc.0c01096

Cited by 17 publications

(7 citation statements)

References 44 publications

(239 reference statements)

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“…Catecholboronates are prone to protodeborylation on silica, which is only prompted with electron-rich substrates such as the ones under study, preventing their direct isolation by chromatographic means. 57,58 A suitable alternative to ease purification is transesterification to a more stable boronate, such as pinacol.…”

Section: ■ Borylation Of Enaminesmentioning

confidence: 99%

A Metal-Free Approach for the C–H Activation and Transfer Borylation of Electron-Rich Alkenes

2022

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Alkenyl boronates are ubiquitous reagents in organic synthesis, as they allow the formation of crucial bonds through crosscoupling reactions. Transition-metal catalysis is the most common approach to this transformation; however, it has limitations in terms of selectivity and boron reagents. On the other hand, metal-free borylation reactions often require the use of harsh reagents, causing compatibility issues. Herein, we apply a metal-free isodesmic borylation strategy, a functional-group-tolerant approach, to the C−H borylation of electron-rich olefins. We show that 2-mercaptoimidazole compounds can efficiently catalyze the borylation of enol ethers, silyl enol ethers, and enamines. Furthermore, borylated compounds can be functionalized in one-pot transformations, making this a useful synthetic tool. The various deactivation pathways are explained and the mechanism is analyzed computationally, revealing that, unlike those of most transition metals, the mechanism occurs through C−H activation rather than a sequence of insertion and elimination. This work highlights transfer C−H borylation as a versatile and tolerant tool for the borylation and functionalization of alkenes.

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Section: ■ Borylation Of Enaminesmentioning

confidence: 99%

A Metal-Free Approach for the C–H Activation and Transfer Borylation of Electron-Rich Alkenes

2022

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“…[92] Recently, the Blum group developed an "Air with Wet Solvents" technique in which the borylated compound in the catechol protection can be isolated. [93]…”

Section: Through Cyclization Approachmentioning

confidence: 99%

“…However, this protocol also has been extended for the siloles, [90] phospholes, [91] and even boroles synthesis [92] . Recently, the Blum group developed an “Air with Wet Solvents” technique in which the borylated compound in the catechol protection can be isolated [93] …”

Section: Through Cyclization Approachmentioning

confidence: 99%

Transition‐Metal‐Free Heterocyclic Carbon‐Boron Bond Formation

Hazra

Mahato

Das

et al. 2022

Chemistry A European J

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Heteroaryl boronic acids and esters are extremely important and valuable intermediates because of their wide application in the synthesis of marketed drugs and bioactive compounds. Over the last couple of decades, the construction of highly important heteroaryl carbon‐boron bonds has created huge attention. The transition‐metal‐free protocols are more green, less sensitive to air and moisture, and also economically advantageous over the transition‐metal‐based protocols. The transition‐metal‐free C−H borylation of heteroarenes and C−X (X=halogen) borylation of heteroaryl halides represents an excellent approach for their synthesis. Also, various cyclization and alkyne activation protocols have been recently established for their synthesis. The goal of this review article is to summarize the existing literature and the current state of the art for transition‐metal‐free synthesis of heteroaryl boronic acid and esters.

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“…After 22 h, the reaction was cooled to 25 °C, and the solvent was removed in vacuo to afford the crude product. The purified product was obtained by flash column chromatography (normal phase and/or reverse phase 52 ) or preparatory thin layer chromatography (prep TLC). The chromatography or prep TLC solvents are described below.…”

Section: Synthesis Of 4-chloro-2-(methylselanyl)aniline (Si-6)mentioning

confidence: 99%

Silyl Radical Cascade Cyclization of 2-Isocyanothioanisole toward 2-Silylbenzothiazoles through Radical Initiator–Inhibitor Symbiosis

Gao

Blum

2022

J. Org. Chem.

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A demethylative silyl radical cascade cyclization of 2-isocyanothioanisoles toward 2-silylated benzothiazole building blocks has been developed. The development of a “radical initiator–inhibitor symbiosis” system solves the challenge of otherwise dominant methyl radical-triggered side reactions brought about by kinetically unfavored generation of reactive silyl radical species. The products accessed in this protocol are amendable to various downstream functionalization reactions, including the quick construction of a topoisomerase II inhibitor via a Hiyama cross-coupling reaction and of an antiviral agent via a fluoride-/hydroxide-free nucleophilic substitution to acyl chloride.

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Borylative Heterocyclization without Air-Free Techniques

Cited by 17 publications

References 44 publications

A Metal-Free Approach for the C–H Activation and Transfer Borylation of Electron-Rich Alkenes

A Metal-Free Approach for the C–H Activation and Transfer Borylation of Electron-Rich Alkenes

Transition‐Metal‐Free Heterocyclic Carbon‐Boron Bond Formation

Silyl Radical Cascade Cyclization of 2-Isocyanothioanisole toward 2-Silylbenzothiazoles through Radical Initiator–Inhibitor Symbiosis

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