Conjugate Addition of Acetal-Derived Benzyl Radicals Generated from Low-Valent Titanium-Mediated C–O Bond Cleavage

Suga, Tetsuya; Nakamura, Masaharu; Takada, Ryusei; Ukaji, Yutaka

doi:10.1246/bcsj.20200364

Cited by 6 publications

(4 citation statements)

References 30 publications

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“…In the subsequent rate-determining stage, the CÀ O bond is directly cleaved, and an alkyl radical is formed without the participation of the CÀ Cl species; subsequently, it reacts with alkenes. In addition to the metalation-protonation pathway as reported in our previous study, [18] the low-valent Ti-promoted HAT from DMA was unexpectedly found to be another route for terminating the radical process, although its proportion would be largely dependent on the alkenes used.…”

Section: Methodssupporting

confidence: 57%

“…Representative cyclopentadienyl (Cp)‐based Ti reagents Cp 2 TiCl 2 and Cp*TiCl 3 demonstrated only slight reactivity to the C−O cleavage (entries 2 and 3). TiCl 4 (collidine) [10] and TiCl 4 (tmeda), [18] which were previously reported by our group, were not very effective (entries 4 and 5). Mn powder as a reductant was less suitable than Zn (entry 6).…”

Section: Resultsmentioning

confidence: 64%

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Direct and Unified Access to Carbon Radicals from Aliphatic Alcohols by Cost‐Efficient Titanium‐Mediated Homolytic C−OH Bond Cleavage

et al. 2022

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Low-valent Ti-mediated homolytic CÀ O bond cleavage offers unified access to carbon radicals from ubiquitous non-activated tertiary, secondary, and even primary alcohols. In contrast to the representative Ti reagents, which were ineffective for this purpose, "TiCl 2 (cat)"/Zn (cat = catecholate) was found to be specifically active. This method was applied to the addition reactions of radicals to alkenes and exhibited high generality and yields. More than 50 combinations were examined. The excellent cost-efficiency and accessibility of "TiCl 2 (cat)"/Zn further enhance its applicability. Control experiments proved the presence of a carbon radical intermediate and excluded the pathway via alkyl chlorides. Further mechanistic study indicated that the 1 : 2 complex of alkoxide (RÀ O À ) and Ti III is an active species in the CÀ O cleavage.

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Section: Methodssupporting

confidence: 57%

Section: Resultsmentioning

confidence: 64%

Direct and Unified Access to Carbon Radicals from Aliphatic Alcohols by Cost‐Efficient Titanium‐Mediated Homolytic C−OH Bond Cleavage

et al. 2022

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“…The same strategy was also applied to the generation of α-alkoxy carbon radicals from benzyl acetals. 16 The radical was subsequently intercepted by acrylonitrile.…”

Section: Scheme 4 Ti-mediated Alcohol C-o Radical Homolysismentioning

confidence: 99%

Recent Progress on Transition-Metal-Mediated Reductive C(sp3)–O Bond Radical Addition and Coupling Reactions

Lin

Chen

et al. 2022

Synthesis

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In this mini review, we summarized the recent development of thermo-driven C(sp3)‒O bond radical scission methods and their applications in the construction of C(sp3)‒C bonds via conjugate additions with activated double bonds and reductive coupling mediated by economic 3d metals, in particular nickel. We assort the review based on the approaches of C(sp3)‒O bond radical scission in three folds (see below). Upon creation of the radical intermediates, subsequent transformation into C(sp3)‒C bonds that enables C(sp3)‒O cross-electrophile coupling with carbon electrophiles are discussed in depth. 1. Direct SET to C(sp3)‒O bond 2. Radical scission of activated C(sp3)‒O bonds via SET to the protecting groups 3. In situ activation of alcohols 4. Summary and outlook

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“…For instance, Suga, Ukaji, and Shu et al developed a direct homolytic cleavage of alcoholic CÀ O bonds under low-valent titanium catalysis. [40][41][42][43][44] Additionally, the oxidative addition modes (metal insertion or nucleophilic attack), catalyzed by transition metals such as Ni, Re, Pd, Au, and Ir, have been applied to the CÀ OH bond cleavage of alcohols, possibly with a subsequent coupling step. Moreover, the CÀ OH bond cleavage via β-OH elimination has been reported in the transition metal Mo/Ru catalyzed reaction systems (Figure 2b).…”

Section: Introductionmentioning

confidence: 99%

Recent DFT Calculations on the Mechanism of Transition‐Metal‐Catalyzed C−O Activation of Alcohols

Liu

et al. 2023

ChemCatChem

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In recent decades, density functional theory (DFT) calculations have been extensively employed to investigate the mechanism of transition metal-catalyzed CÀ O activation reactions. These studies provide valuable insights into the structure-reactivity/ selectivity correlations via theoretical simulations and energy profile analysis. Alcohols, a category of molecules that are readily available from biomass and are low cost, represent one of the most extensively studied compounds in organic syn-thesis. In this review, we provide a brief overview of the DFT studies conducted since 2017 on the CÀ OH bond activation of alcohols catalyzed by transition metals. Specifically, the activation can be mainly divided into four categories: free radical cleavage, metal insertion, nucleophilic attack, and β-OH elimination. We will also cover some promising strategies and give a perspective regarding future research directions in this field.

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Conjugate Addition of Acetal-Derived Benzyl Radicals Generated from Low-Valent Titanium-Mediated C–O Bond Cleavage

Cited by 6 publications

References 30 publications

Direct and Unified Access to Carbon Radicals from Aliphatic Alcohols by Cost‐Efficient Titanium‐Mediated Homolytic C−OH Bond Cleavage

Direct and Unified Access to Carbon Radicals from Aliphatic Alcohols by Cost‐Efficient Titanium‐Mediated Homolytic C−OH Bond Cleavage

Recent Progress on Transition-Metal-Mediated Reductive C(sp3)–O Bond Radical Addition and Coupling Reactions

Recent DFT Calculations on the Mechanism of Transition‐Metal‐Catalyzed C−O Activation of Alcohols

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