Site-Selective C–H Functionalization by Decatungstate Anion Photocatalysis: Synergistic Control by Polar and Steric Effects Expands the Reaction Scope

Ravelli, Davide; Fagnoni, Maurizio; Fukuyama, Takahide; Nishikawa, Takeshi; Ryu, Ilhyong

doi:10.1021/acscatal.7b03354

Cited by 364 publications

(294 citation statements)

References 165 publications

(120 reference statements)

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“…[15] An alkyl bromide was converted into product 12 in [a] Combined yield of the isolated products. Cyclic hydrocarbons with different ring sizes provided alkylation products 4-8 in good to excellent yields (Scheme 4).…”

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confidence: 99%

Microtubing‐Reactor‐Assisted Aliphatic C−H Functionalization with HCl as a Hydrogen‐Atom‐Transfer Catalyst Precursor in Conjunction with an Organic Photoredox Catalyst

2018

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Chlorine radical, which is classically generated by the homolysis of Cl under UV irradiation, can abstract a hydrogen atom from an unactivated C(sp )-H bond. We herein demonstrate the use of HCl as an effective hydrogen-atom-transfer catalyst precursor activated by an organic acridinium photoredox catalyst under visible-light irradiation for C-H alkylation and allylation. The key to success relied on the utilization of microtubing reactors to maintain the volatile HCl catalyst. This photomediated chlorine-based C-H activation protocol is effective for a variety of unactivated C(sp )-H bond patterns, even with primary C(sp )-H bonds, as in ethane. The merit of this strategy is illustrated by rapid access to several pharmaceutical drugs from abundant unfunctionalized alkane feedstocks.

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confidence: 99%

Microtubing‐Reactor‐Assisted Aliphatic C−H Functionalization with HCl as a Hydrogen‐Atom‐Transfer Catalyst Precursor in Conjunction with an Organic Photoredox Catalyst

2018

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“…Selective alkylation proceeded at more hydridic CÀHbonds in cyclopentanone and cycloheptanone (products 10 and 11)b ecause of the electrophilic nature of chlorine radical. [15] An alkyl bromide was converted into product 12 in [a] Combined yield of the isolated products. [b] Diastereoselectivity and regioselectivity,w here relevant, were determined by analysis of the 1 HNMR spectrum of the crude product.…”

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confidence: 99%

Microtubing‐Reactor‐Assisted Aliphatic C−H Functionalization with HCl as a Hydrogen‐Atom‐Transfer Catalyst Precursor in Conjunction with an Organic Photoredox Catalyst

Deng

Zhou

2018

Angewandte Chemie

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Chlorine radical, which is classically generated by the homolysis of Cl 2 under UV irradiation, can abstract ah ydrogen atom from an unactivated C(sp 3 )ÀHb ond. We herein demonstrate the use of HCl as an effective hydrogenatom-transfer catalyst precursor activated by an organic acridinium photoredoxc atalyst under visible-light irradiation for C À Halkylation and allylation. The key to success relied on the utilization of microtubing reactors to maintain the volatile HCl catalyst. This photomediated chlorine-based CÀHactivation protocol is effective for avariety of unactivated C(sp 3 )ÀH bond patterns,e ven with primary C(sp 3 )ÀHb onds,a si n ethane.The merit of this strategy is illustrated by rapid access to several pharmaceutical drugs from abundant unfunctionalized alkane feedstocks.Dramatic developments in photocatalysis over the past decade have enabled previously inaccessible transformations. [1] In particular,t he synergistic combination of photoredox catalysts and hydrogen-atom-transfer (HAT) catalysts has offered enormous opportunities for C(sp 3 ) À Ha ctivation. [2] In general, upon irradiation with light, the activated photocatalyst can oxidize the HATc atalyst through singleelectron transfer (SET) to form ahydrogen abstractor,either in the presence or absence of abase;the hydrogen abstractor will abstract ah ydrogen atom to deliver ac arbon radical to enable C À Hactivation (Scheme 1a). In this context, avariety of HATc atalysts based on S( thiols), [3] N( quinuclidines, sulfonamides), [4] and O( benzoates, N-hydroxides) [5] have been developed (Scheme 1b). However, the development of readily available and highly efficient catalytic systems that accommodate aw ide range of CÀHp atterns without the requirement of stoichiometric amounts of additives is still highly desirable.Chlorine radical, classically generated by the homolysis of Cl 2 under UV irradiation, represents another heteroatomcentered radical capable of abstracting hydrogen atoms from unactivated aliphatic CÀHb onds.H owever,i th as not been widely recognized as aH AT catalyst under conditions of visible-light irradiation. In this regard, Doyle and co-workers and our group recently demonstrated the generation of chlorine radical by photolysis of aNi III chloride intermediate generated by photoredox-mediated single-electron oxidation of aNi II precursor and showed that it could activate C(sp 3 )ÀH bonds for arylation [6] and hydroalkylation of alkynes, [7] respectively (Scheme 2a). [8] However,t he former reaction uses stoichiometric amounts of chloride compounds,a nd the latter suffered from limited scope with respect to the C À H substrate.B oth methods required excess amounts of CÀH substrates (! 10 equiv) for effective transformations. Scheme 1. Synergistic merging of photoredox and HATcatalysis.

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“…Evidence for the stereospecificity of the reaction was also provided by the oxidation of an optically pure ester substrate,w hich was hydroxylated with complete stereoretention (Scheme 50). 7 to oxidize remote aliphatic C À Hbonds of protonated amines. [70] Pyrrolidine was selected as the model substrate and reaction optimization was carried out by high-throughput experimentation, whereby tetrabutylammonium decatungstate (TBADT) was screened with different oxidants,a cids,a nd solvents for ap hotochemical reaction.…”

Section: Reviewsmentioning

confidence: 99%

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes.…”

Section: Introductionmentioning

confidence: 99%

“…Among the available methods for the site-selective functionalization of aliphatic CÀHb onds,t hose based on hydrogen atom transfer (HAT) to radical or radical-like species play an important role. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes.…”

Section: Introductionmentioning

confidence: 99%

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Activation and Deactivation Strategies Promoted by Medium Effects for Selective Aliphatic C−H Bond Functionalization

Bietti

2018

Angew Chem Int Ed

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Selective functionalization of unactivated aliphatic C-H bonds represents an important goal of modern synthetic chemistry. Differentiating between such bonds in organic molecules with high levels of selectivity remains a crucial issue, and a profound understanding of even the subtlest reactivity trends is needed. Among the methods that have been developed, those based on hydrogen atom transfer (HAT) have attracted considerable interest. Within this framework, medium effects have proved effective in altering the reactivity and site selectivity in synthetically useful C-H functionalization procedures. In this Review, the mechanistic features behind the available strategies are discussed. It is shown that hydrogen bonding and acid-base interactions can promote C-H bond activation or deactivation toward HAT reagents, thereby providing fine-control over the site selectivity and product chemoselectivity as well as useful guidelines for future development and applications.

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Site-Selective C–H Functionalization by Decatungstate Anion Photocatalysis: Synergistic Control by Polar and Steric Effects Expands the Reaction Scope

Cited by 364 publications

References 165 publications

Microtubing‐Reactor‐Assisted Aliphatic C−H Functionalization with HCl as a Hydrogen‐Atom‐Transfer Catalyst Precursor in Conjunction with an Organic Photoredox Catalyst

Microtubing‐Reactor‐Assisted Aliphatic C−H Functionalization with HCl as a Hydrogen‐Atom‐Transfer Catalyst Precursor in Conjunction with an Organic Photoredox Catalyst

Microtubing‐Reactor‐Assisted Aliphatic C−H Functionalization with HCl as a Hydrogen‐Atom‐Transfer Catalyst Precursor in Conjunction with an Organic Photoredox Catalyst

Activation and Deactivation Strategies Promoted by Medium Effects for Selective Aliphatic C−H Bond Functionalization

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