Autocatalytic Carbonyl Arylation through In Situ Release of Aryl Nucleophiles from N ‐Aryl‐ N ′‐Silyldiazenes

2021

Chemistry A European J

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A chemoselective C(sp 2 )À C(sp 2 ) coupling of sufficiently electron-deficient fluorinated arenes and functionalized N-aryl-N'-silyldiazenes as masked aryl nucleophiles is reported. The fluoride-promoted transformation involves the in situ generation of the aryl nucleophile decorated with various sensitive functional groups followed by a stepwise nucleophilic aromatic substitution (S N Ar). These reactions typically proceed at room temperature within minutes. This catalytic process allows for the functionalization of both coupling partners, furnishing highly fluorinated biaryls in good yields.Polyfluorinated biaryls have been identified as versatile and robust building blocks possessing interesting properties relevant for agrochemicals, pharmaceuticals, and materials science. [1,2] Hence, the development of viable synthetic strategies for their preparation through C(sp 2 )À C(sp 2 ) bond-forming reactions continues to attract significant interest. [3] Typical approaches to access this motif engage transition-metal catalysts (Scheme 1, top left). [4][5][6][7] Among them, conventional cross-coupling [4] and oxidative direct arylation [5] generally require the prefunctionalization of a coupling partner while cross-dehydrogenative coupling [6] involves non-prefunctionalized arenes. These transformations normally operate at elevated temperature and require long reaction times. As a result, the chemoselectivity of these methods can be deteriorated, and sensitive functional groups poorly tolerated, especially on the electron-deficient aromatic ring. Also, transition-metal-free approaches have been far less explored. [8][9][10][11] Radical couplings have been identified as a valuable alternative (Scheme 1, top right). [8] Recently, König and co-workers disclosed a photocatalytic process involving formal CÀ H bond activation that proceeds at 40°C yet requiring 72 h. [9] While the polyfluorinated [a

Section: Methodsmentioning

confidence: 71%

“…Nucleophilic addition of the aryl nucleophile to DMF had never been observed with our system before. [14a] …”

mentioning

confidence: 99%

Transition‐Metal‐Free Coupling of Polyfluorinated Arenes and Functionalized, Masked Aryl Nucleophiles

2021

Chemistry A European J

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“…Several bases expected to promote the NÀ Si bond cleavage were examined. [14] Owing to their poor solubility, K 2 CO 3 and CsF resulted in low conversion of the starting materials while NaOtBu afforded product 6 aa in 63 % yield (entries 9-11).…”

Section: Methodsmentioning

confidence: 99%

“…[13] These N-aryl-N'-silyldiazenes are kinetically stable and have already been employed with loss of dinitrogen as aryl pronucleophiles. [14,15] We asked ourselves whether the same set of silylated diazenes could serve as precursors for diazenyl anions without extrusion of dinitrogen (Scheme 2, top). Diazenes are assumed intermediates in denitrogenative palladium-catalyzed cross-coupling reactions of arylhydrazine derivatives and aryl halides to form biaryls.…”

Section: Sincementioning

confidence: 99%

Synthesis of Non‐Symmetric Azoarenes by Palladium‐Catalyzed Cross‐Coupling of Silicon‐Masked Diazenyl Anions and (Hetero)Aryl Halides

2022

Angew Chem Int Ed

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The photoswitchable motif of azobenzenes is of great importance across the life and materials sciences. This maintains a constant demand for their efficient synthesis, especially that of non-symmetric derivatives. We disclose here a general strategy for their synthesis through an unprecedented C(sp 2 )À N(sp 2 ) cross-coupling where functionalized aryl-substituted diazenes masked with a silyl group are employed as diazenyl pronucleophiles. These equivalents of fragile diazenyl anions couple with a diverse set of (hetero)aryl bromides under palladium catalysis with no loss of dinitrogen. The competing denitrogenative biaryl formation is fully suppressed. The reaction requires only a minimal excess, that is 1.2 equivalents, of the diazenyl component. By this, a broad range of azoarenes decorated with two electron-rich/deficient aryl groups can be accessed in a predictable way with superb functional-group tolerance.

“…[17] Die Wahl dieser Reaktionsparameter geschah auf der Grundlage unserer früheren Erfahrung mit der Aktivierung der silylierten Diazene; die Freisetzung von Distickstoff ist in polaren Lösungsmitteln, in denen die silaphile Lewis-Base größtenteils gelöst ist, wahrscheinlicher. [14] Ein Kontrollexperiment in THF als Lösungsmittel zeigte allerdings, dass weder der Verlust von Distickstoff (in Spuren) noch die anvisierte Kupplung ablief; stattdessen wurde die Defunktionalisierung des Arylbromids nachgewiesen. Cs 2 CO 3 in Toluol erschien uns vielversprechend, und wir legten die Reaktionstemperatur auf 60 °C an Stelle von 110 °C fest, um die Abspaltung von Distickstoff nicht zu begünstigen.…”

unclassified

Synthese von unsymmetrischen Azobenzolen durch palladiumkatalysierte Kreuzkupplung von siliciummaskierten Diazenylanionen und (Hetero)arylhalogeniden

2022

Angewandte Chemie

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Das photoschaltbare Motiv von Azobenzolen nimmt eine bedeutende Stellung in den Lebens-und Materialwissenschaften ein. Das hält einen steten Bedarf an deren effizienter Synthese aufrecht, was besonders für unsymmetrische Derivate gilt. Wir stellen hier eine allgemeine Strategie zu deren Darstellung vor, bei der in einer neuartigen C(sp 2 )À N(sp 2 )-Kreuzkupplung funktionalisierte arylsubstituierte, mit einer Silylgruppe maskierte Diazene als Diazenylpronukleophile eingesetzt werden. Diese Entsprechungen für recht instabile Diazenylanionen kuppeln unter Palladiumkatalyse mit einer breitgefächerten Palette an (Hetero)arylbromiden ohne Verlust von Distickstoff. Die konkurrierende Biarylbildung unter Abspaltung von Distickstoff ist vollständig unterdrückt. Die Reaktion erfordert nur einen geringen Überschuss von 1.2 Äquivalenten der Diazenylkomponente. Auf diese Weise werden unzählige Azobenzole mit elektronenreichen/-armen Arylresten unter ausgezeichneter Toleranz gegenüber funktionellen Gruppen planbar zugänglich gemacht.