Ruthenium-Catalyzed Cycloisomerization of 2-Alkynylanilides: Synthesis of 3-Substituted Indoles by 1,2-Carbon Migration

Watanabe, Takuma; Mutoh, Yuichiro; Saito, Shinichi

doi:10.1021/jacs.7b04564

Cited by 83 publications

(41 citation statements)

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“…We assume that the substituent at the benzene ring of the α‐methylstyryl group should simultaneously affect the reactivity of the alkynyl and the isopropenyl groups, and some side reactions should thus occur during the expected 1,2‐carbon migration/carbocyclization. A similar complicated substituent effect was observed in our previously reported indole synthesis …”

Section: Methodssupporting

confidence: 84%

“…Meanwhile, we have developed the first catalytic reaction that involves the vinylidene rearrangement of internal alkynes by 1,2‐carbon migration . In the presence of the cationic ruthenium catalyst [CpRu(dppe)] + (Cp=η 5 ‐C 5 H 5 − ; dppe=Ph 2 PCH 2 CH 2 PPh 2 ), various 2‐alkynylanilides are converted into the corresponding 3‐substituted indoles in high yields via the 1,2‐carbon migration followed by a carbon‐nitrogen bond‐forming cyclization.…”

Section: Methodsmentioning

confidence: 99%

“…Initially, we investigated the impact of the structure of the styrene moiety in 2‐(phenylethynyl)styrene derivatives ( 1 ) on the carbocyclization using [CpRuCl(dppe)]/NaBAr F 4 ⋅2 H 2 O (Ar F =3,5‐(CF 3 ) 2 C 6 H 3 ) as the catalytic system, which was found to be highly active in the previous studies . When a mixture of 2‐(phenylethynyl)styrene ( 1 a ), [CpRuCl(dppe)] (10 mol %), and NaBAr F 4 ⋅2 H 2 O (12 mol %) was stirred at 130 °C for 2 h in xylene, the desired 1,2‐aryl migration product, 1‐phenylnaphthalene ( 2 a ), was formed in 74 % yield (Table ).…”

Section: Methodsmentioning

confidence: 99%

“…Meanwhile, we have developed the first catalytic reaction that involves the vinylidener earrangemento fi nternal alkynes by 1,2-carbon migration. [14] In the presenceo ft he cationic ruthenium catalyst [CpRu(dppe)] + (Cp = h 5 -C 5 H 5 À ;d ppe = Ph 2 PCH 2 CH 2 PPh 2 ), various 2-alkynylanilides are converted into the corresponding 3-substituted indoles in high yields via the 1,2-carbon migration followed by ac arbon-nitrogen bondforming cyclization. These results encouraged us to develop new and useful reactions that involve1 ,2-carbon migration and carbon-carbon bond formation.H erein, we report ar uthenium-catalyzed cycloisomerization of 2-alkynylstyrenes that generates substituted naphthalenesv ia 1,2-carbon migration (Scheme 1c).…”

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confidence: 99%

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Ruthenium‐Catalyzed Cycloisomerization of 2‐Alkynylstyrenes via 1,2‐Carbon Migration That Leads to Substituted Naphthalenes

Watanabe

Abe

Mutoh

et al. 2018

Chemistry A European J

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Section: Methodssupporting

confidence: 84%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Ruthenium‐Catalyzed Cycloisomerization of 2‐Alkynylstyrenes via 1,2‐Carbon Migration That Leads to Substituted Naphthalenes

Watanabe

Abe

Mutoh

et al. 2018

Chemistry A European J

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“…Subsequently, we reported the synthesis of alkynylmethylidene‐benzoxasiloles from 2‐(alkynylsilylethynyl)phenols through 1,2‐silicon migration to form rhodium vinylidenes followed by 1,3‐carbon (alkyne) migration (Scheme , top) . Although there are several examples of transition‐metal‐catalyzed cycloisomerization reactions involving silicon or carbon migration, no transition‐metal‐catalyzed cycloisomerization reaction involving both the silicon and carbon migrations has been reported to date. Pleasingly, the thus obtained trimethylsilylethynylmethylidene‐benzoxasilole was transformed into benzofuranylmethylidene‐benzoxasilole 2 c , which showed high fluorescence quantum yields in both solution and powder states (Scheme , top) .…”

Section: Introductionmentioning

confidence: 99%

Rhodium‐Catalyzed Cascade Synthesis of Benzofuranylmethylidene‐Benzoxasiloles: Elucidating Reaction Mechanism and Efficient Solid‐State Fluorescence

Namba

Hayashi

Kawauchi

et al. 2018

Chemistry A European J

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A new synthetic route to highly fluorescent benzofuranylmethylidenebenzoxasiloles through cationic rhodium(I)/binap complex-catalyzed cascade cycloisomerization of bis(2-ethynylphenol)silanes has been developed involving 1,2-silicon and 1,3-carbon (alkyne) migrations followed by oxycyclization. The present synthesis requires only three steps, starting from commercially available dichlorodiisopropylsilane, which is markedly shorter than our previous synthesis (eight steps starting from commercially available chlorodiisopropylsilane). Theoretical calculations elucidated the mechanism of the above cascade cycloisomerization. This reaction is initiated by the formation of a rhodium vinylidene not through direct 1,2-silicon migration but rather through an unprecedented stepwise 1,5-silicon migration followed by C-Si bond-forming cyclization from a dearomatized allenylrhodium complex. Subsequent 1,3-carbon (alkyne) migration leading to a η -allenyl/propargyl-rhodium complex followed by oxycyclization through π-bond (alkyne) activation with the cationic rhodium(I) complex affords the benzofuranylmethylidenebenzoxasilole product. The structure-fluorescence property relationships of the thus obtained benzofuranylmethylidenebenzoxasiloles were investigated, which revealed that good fluorescence quantum yields were generated in the solution state (φ =69-87 %) by introduction of electron-donating alkyl and phenyl groups on two phenoxy groups. In the powder state, 4-methyl- and 4-methoxy-phenoxy derivatives exhibited efficient blue fluorescence (φ =52 % and 46 %, respectively). Especially, the 4-methylphenoxy derivative was thermally stable, and exhibited strong narrow-band fluorescence in the film state (blue, φ =95 %) and redshifted strong narrow-band fluorescence (green, φ =90 %) in the crystalline state as a result of the formation of an offset π-stacked dimer; the latter was confirmed by X-ray crystallographic analysis and by theoretical calculations.

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Vinylidene Complexes

Iwamoto

Ishii

2022

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The parent vinylidene CCH 2 and its substituted analogs CCRR′ are highly unstable isomers of the corresponding alkyne, HCCH and RCCR′, respectively. However, vinylidene complexes, which can be denoted as MCCRR′ in the mononuclear case, are often more stable than η 2 ‐alkyne complexes, and in fact, the most common preparation method for vinylidene complexes is the direct reaction of alkynes (terminal alkynes in most cases) with coordinatively unsaturated metal complexes, although the relative stability of vinylidene and η 2 ‐alkyne complexes depends on the nature of the metal center. The vinylidene ligand may be viewed as an α,β‐unsaturated type of carbene, and the MCCRR′ backbone may also be regarded as a metallaallene. The vinylidene ligand often exhibits a π‐acidic nature, and its character somewhat resembles Fischer‐type carbenes. As a result, vinylidene complexes are widely seen with middle to late transition metals, most typically groups 6, 7, 8, and 9 metals in relatively low oxidation state (typically 0 to III). Owing to its versatile reactivities, vinylidene complexes work as intermediates in many catalytic and stoichiometric conversions of alkynes. Surface vinylidene species are also considered to take part in heterogeneous catalysis such as Fischer–Tropsch reaction, and multinuclear vinylidene complexes are expected to serve as molecular models for such surface species. This article summarizes bonding and structure, physicochemical properties, synthesis, and reactivities including catalytic applications of vinylidene complexes.

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Ruthenium-Catalyzed Cycloisomerization of 2-Alkynylanilides: Synthesis of 3-Substituted Indoles by 1,2-Carbon Migration

Abstract: We developed ruthenium-catalyzed cycloisomerization of alkynylanilides that gave 3-substituted indoles in high yields. The reaction proceeded via the disubstituted vinylidene ruthenium complex that was formed by the 1,2-carbon migration.

Cited by 83 publications

References 86 publications

Ruthenium‐Catalyzed Cycloisomerization of 2‐Alkynylstyrenes via 1,2‐Carbon Migration That Leads to Substituted Naphthalenes

Ruthenium‐Catalyzed Cycloisomerization of 2‐Alkynylstyrenes via 1,2‐Carbon Migration That Leads to Substituted Naphthalenes

Rhodium‐Catalyzed Cascade Synthesis of Benzofuranylmethylidene‐Benzoxasiloles: Elucidating Reaction Mechanism and Efficient Solid‐State Fluorescence

Vinylidene Complexes

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