Coupling of Quinone Monoacetals Promoted by Sandwiched Brønsted Acids: Synthesis of Oxygenated Biaryls

Dohi, Toshifumi; Washimi, Naohiko; Kamitanaka, Tohru; Fukushima, Kazuki; Kita, Yasuyuki

doi:10.1002/anie.201101646

Cited by 60 publications

(26 citation statements)

References 43 publications

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“…palladium based) generate a large amount of toxic waste in this approach. [18] An elegant electroorganic alternative is described by the cation pool method established by Yoshida et al to prevent undesired homocoupling products. [11][12][13][14][15] This approach has been addressed by a variety of efficient protocols.…”

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confidence: 99%

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

et al. 2016

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The oxidative cross-coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2'-biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent-free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale-up and inherently safe. The implementation of O-silyl-protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2,2'-biphenols. The use of a bulky silyl group to block one hydroxyl moiety makes the final product less prone to oxidation. Furthermore, the partially silyl-protected 2,2'-biphenols are versatile building blocks that usually require tedious or low-yielding synthetic pathways. Additionally, this strategy facilitates a large variety of new substrate combinations for oxidative cross-coupling reactions.

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confidence: 99%

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

et al. 2016

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“…[6] Thes carcity of reliable methods is surprising as these atropoisomeric but non-C 2 -symmetrical biaryldiols have been shown to be excellent ligands or catalysts in many catalytic reactions, especially in those where the C 2 -symmetrical scaffolds were found to be ineffective. [12] Surprisingly, traditional Brønsted or Lewis acids were found to be completely ineffective in these studies.W ea rgued that if quinone monoacetals (1)w ere reacted with unprotected naphthols (2)i nt he presence of as trong Brønsted acid catalyst, an acetal exchange would afford the corresponding mixed-acetals (3;S cheme 1). Thecoupling of quinone monoacteals with alkoxyarenes has only been demonstrated in the presence of solid acids such as montmorillonite (MT) clay.…”

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confidence: 89%

“…[12] Surprisingly, traditional Brønsted or Lewis acids were found to be completely ineffective in these studies.W ea rgued that if quinone monoacetals (1)w ere reacted with unprotected naphthols (2)i nt he presence of as trong Brønsted acid catalyst, an acetal exchange would afford the corresponding mixed-acetals (3;S cheme 1). However,m oderate yield of 5a was obtained at reflux (entries [11][12][13][14]. [13] To test the hypothesis outlined above,w eb egan to look for suitable combinations of strong organic acids (i.e., Brønsted acids) and solvents (Table 1).…”

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Practical Organocatalytic Synthesis of Functionalized Non‐C₂‐Symmetrical Atropisomeric Biaryls

Gao

Keene

et al. 2015

Angewandte Chemie

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An organic acid catalyzedd irect arylation of aromatic C(sp 2 )ÀHb onds in phenols and naphthols for the preparation of 1,1'-linked functionalizedb iaryls was developed. The products are non-C 2 -symmetrical, atropoisomeric, and represent previously untapped chemical space.Overall this transformation is operationally simple,d oes not require an external oxidant, is readily scaled up (up to 98 mmol), and the structurally diverse 2,2'-dihydroxy biaryl (i.e., BINOL-type), as well as 2-amino-2'-hydroxy products (i.e., NOBIN-type) are formed with complete regioselectivity.D ensity-functional calculations suggest that the quinone and imino-quinone monoacetal coupling partners are exclusively arylated at their aposition by an asynchronous [3,3]-sigmatropic rearrangement of am ixed acetal species whichi sf ormed in situ under the reaction conditions.

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“…In recognition of this difficulty, we recently proposed a coupling strategy that alternatively relied on the reversible dearomatization–rearomatization utility of phenols for incorporating external aryl molecules. The method involves the formation of quinone monoacetals by the phenol dearomatization using PIDA followed by the aryl coupling induced by acid activators accompanying rearomatization . The development of an efficient oxidative biaryl cross‐coupling of phenols is thus challenging and there were no reports of the coupling at the phenol para positions under metal‐free conditions.…”

Section: Cross‐coupling Challengementioning

confidence: 99%

Pioneering Metal‐Free Oxidative Coupling Strategy of Aromatic Compounds Using Hypervalent Iodine Reagents

Kita

Dohi

2015

The Chemical Record

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122

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We started our hypervalent iodine research about 30 years ago in the mid-1980s. We soon successfully developed the single-electron-transfer oxidation ability of a hypervalent iodine reagent, specifically, phenyliodine(III) bis(trifluoroacetate) (PIFA), toward aromatic rings of phenyl ethers for forming aromatic cation radicals. This was one of the exciting and unexpected events in our research studies so far, and the discovery was reported in 1991. It also led to the next challenge, developing the metal-free oxidative couplings for C-H functionalizations and direct couplings between the C-H bonds of valuable aromatic compounds in organic synthesis. In order to realize the effective oxidative coupling, pioneering new aromatic ring activations was essential and several useful methodologies have been found for oxidizable arenes. The achievements regarding this objective obtained in our continuous research are herein summarized with classification of the aromatic ring activation strategies.

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Coupling of Quinone Monoacetals Promoted by Sandwiched Brønsted Acids: Synthesis of Oxygenated Biaryls

Cited by 60 publications

References 43 publications

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

Practical Organocatalytic Synthesis of Functionalized Non‐C₂‐Symmetrical Atropisomeric Biaryls

Pioneering Metal‐Free Oxidative Coupling Strategy of Aromatic Compounds Using Hypervalent Iodine Reagents

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Coupling of Quinone Monoacetals Promoted by Sandwiched Brønsted Acids: Synthesis of Oxygenated Biaryls

Cited by 60 publications

References 43 publications

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

Practical Organocatalytic Synthesis of Functionalized Non‐C2‐Symmetrical Atropisomeric Biaryls

Pioneering Metal‐Free Oxidative Coupling Strategy of Aromatic Compounds Using Hypervalent Iodine Reagents

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Practical Organocatalytic Synthesis of Functionalized Non‐C₂‐Symmetrical Atropisomeric Biaryls