Synthetic and Predictive Approach to Unsymmetrical Biphenols by Iron-Catalyzed Chelated Radical–Anion Oxidative Coupling

Libman, Anna; Shalit, Hadas; Vainer, Yulia; Narute, Sachin; Kozuch, Sebastian; Pappo, Doron

doi:10.1021/jacs.5b06494

Cited by 162 publications

(133 citation statements)

References 69 publications

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“…The principle behind this finding plays a vital role in determining the selectivity of radical–radical coupling reactions. Two reactivity indices that were introduced by Domingo and co-workers for free radicals, the global electrophilicity ω ° and global nucleophilicity N °62, have been used to clarify the origin of the selectivity in this work (Table 1)697071, and a graphic illustration for the cross-coupling selectivity is also provided based on these data (Fig. 12).…”

Section: Resultsmentioning

confidence: 99%

Stabilization of Two Radicals with One Metal: A Stepwise Coupling Model for Copper-Catalyzed Radical–Radical Cross-Coupling

Zhu

Bai

et al. 2017

Sci Rep

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Transition metal-catalyzed radical–radical cross-coupling reactions provide innovative methods for C–C and C–heteroatom bond construction. A theoretical study was performed to reveal the mechanism and selectivity of the copper-catalyzed C–N radical–radical cross-coupling reaction. The concerted coupling pathway, in which a C–N bond is formed through the direct nucleophilic addition of a carbon radical to the nitrogen atom of the Cu(II)–N species, is demonstrated to be kinetically unfavorable. The stepwise coupling pathway, which involves the combination of a carbon radical with a Cu(II)–N species before C–N bond formation, is shown to be probable. Both the Mulliken atomic spin density distribution and frontier molecular orbital analysis on the Cu(II)–N intermediate show that the Cu site is more reactive than that of N; thus, the carbon radical preferentially react with the metal center. The chemoselectivity of the cross-coupling is also explained by the differences in electron compatibility of the carbon radical, the nitrogen radical and the Cu(II)–N intermediate. The higher activation free energy for N–N radical–radical homo-coupling is attributed to the mismatch of Cu(II)–N species with the nitrogen radical because the electrophilicity for both is strong.

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Section: Resultsmentioning

confidence: 99%

Stabilization of Two Radicals with One Metal: A Stepwise Coupling Model for Copper-Catalyzed Radical–Radical Cross-Coupling

Zhu

Bai

et al. 2017

Sci Rep

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“…[16d, 17b, 18] Often fluorinated alcohols interfere with the catalytic cycle and positively affect the kinetic profile of polar reactions, significantly improving their efficiency [18,19] and selectivity. [20] With the notion that fluorinated alcohols can act as solvent-assisted selectivity in oxidation processes, we studied the autoxidation of methylarene by using the NHPI/Co(OAc) 2 catalytic system in HFIP.…”

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confidence: 99%

Selective Aerobic Oxidation of Methylarenes to Benzaldehydes Catalyzed by N‐Hydroxyphthalimide and Cobalt(II) Acetate in Hexafluoropropan‐2‐ol

2017

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Efficient and highly selective catalytic conditions for the aerobic autoxidation of methylarenes to benzaldehydes, based on N-hydroxyphthalimide (NHPI) and cobalt(II) acetate in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP), were developed. The sustainable conditions enable a multigram scale preparation of benzaldehyde derivatives in high efficiency and with excellent chemoselectivity (up to 99 % conversion and 98 % selectivity).

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“…[19] Jeganmohan and co-workers also described an oxidative cross-coupling of two different phenols using K 2 S 2 O 8 and Bu 4 N + HSO 3 À (10 mol %) in CF 3 COOH. [20] More recently,t he iron-catalyzed oxidative cross-coupling reaction of two different phenols was achieved by the group of Pappo, [21] in which the cross-coupling selectivities of two different phenols are nicely controlled.…”

Section: Methodsmentioning

confidence: 99%

Organo‐Iodine(III)‐Catalyzed Oxidative Phenol–Arene and Phenol–Phenol Cross‐Coupling Reaction

et al. 2016

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The direct oxidative coupling reaction has been an attractive tool for environmentally benign chemistry.Reported herein is that the hypervalent iodine catalyzed oxidative metalfree cross-coupling reaction of phenols can be achieved using Oxone as at erminal oxidant in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP). This method features ah igh efficiency and regioselectivity,a sw ell as functional-group tolerance under very mild reaction conditions without using metal catalysts.The biaryl unit including phenol is an important structural motif for aw ide range of functional molecules such as bioactive natural products,l iquid crystals,a nd ligands for transition-metal catalysts.[1] Thec ommon approaches to the syntheses of these structures involve cross-couplings between aryl halides and organometallic reagents.[2] In these cases of multistep syntheses,s uch as Suzuki or Stille coupling,t he phenol moiety usually has to be protected. Recently,t ransition-metal-catalyzed direct functionalization of the CÀH bonds on aromatic compounds,involving the activation of the aromatic C À Hbond, has attracted much attention in terms of synthetic efficiencya nd minimization of atomic waste. [3,4] In contrast, the oxidative cross-coupling of unprotected phenols has received considerable attention because of the atom-economical and environmentally friendly processes. [5] Although various kinds of homocoupling reactions of unprotected phenols involving the use of Fe,C u, Mn, and Ti salts have been developed, [6] thecatalytic oxidative cross-coupling reaction of phenols by CÀH/CÀH' coupling has remained challenging. [7] This reaction is ac hallenge because,w hen simple phenols are employed in oxidative cross-couplings,the desired products are often concomitantly formed along with homocoupling by-products.M oreover,t he formation of higher-molecular-weight polymers or C,O-connected phenol portions,for example,quinol ethers,might also occur depending on the oxidant and the reaction conditions.[2b] Am ajor reason for this side reaction is the difficulty associated with the tunable reactivity of phenols by controlling their oxidation potential using aprotecting group for the phenol hydroxy group.T herefore,t he development of an efficient catalytic cross-coupling of unprotected phenols for the construction of biaryl compounds is still highly desirable.R ecently,W aldvogel and co-workers reported an electrochemical phenolarene cross-coupling reaction using boron-doped diamond electrodes.[8] Very recently,the iron-catalyzed oxidative crosscoupling reaction of phenols with arenes was successfully achieved.[9] While recent metal-catalyzed cross-couplings of phenols have been studied, the organocatalytic cross-coupling reaction still remains particularly challenging.R ecently,w e developed the oxidative cross-coupling reaction of aromatic compounds using hypervalent iodine reagents. [10][11][12][13][14][15] Inspired by these studies,wenow report abroadly applicable organoiodine(III)-catalyzed oxidative cross-coupling reaction of pheno...

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Synthetic and Predictive Approach to Unsymmetrical Biphenols by Iron-Catalyzed Chelated Radical–Anion Oxidative Coupling

Cited by 162 publications

References 69 publications

Stabilization of Two Radicals with One Metal: A Stepwise Coupling Model for Copper-Catalyzed Radical–Radical Cross-Coupling

Stabilization of Two Radicals with One Metal: A Stepwise Coupling Model for Copper-Catalyzed Radical–Radical Cross-Coupling

Selective Aerobic Oxidation of Methylarenes to Benzaldehydes Catalyzed by N‐Hydroxyphthalimide and Cobalt(II) Acetate in Hexafluoropropan‐2‐ol

Organo‐Iodine(III)‐Catalyzed Oxidative Phenol–Arene and Phenol–Phenol Cross‐Coupling Reaction

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