Über die Reduktion aromatischer Diazoverbindungen mit äthern, 1.3‐Dioxolanen und tertiären Aminen

Abstract

Es wird die Reduktion aromatischer Diazoverbindungen zu den entspr. ArH-Verbindungen in wäß-riger, acetat-gepufferter Lösung unter Verwendung der mit Wasser mischbaren Äther: Dioxan, Tetrahydrofuran, Glykol-dimethyläther und 1.3-Dioxolan beschrieben. Als Oxydationsprodukte der Äther entstehen deren Monoxy-Verbindungen. Der Reaktionsmechanismus wird erörtert. Die Reaktion der Aryldiazonium-fluoroborate mit Isobornyl-alkyläthern in Acetonitril-Lösung liefert neben den ArH-Verbindungen an Stelle der erwarteten, bekannten O-Alkyl-campheroxonium-fluoroborate unter Mitbeteiligung des Acetonitrils Nitrilium-fluoroborate. Bei der Reduktion verschiedener Diazonium-fluoroborate mit 2-Methyl-und 2-Phenyl-1.3-dioxolan konnten die neben den ArH-Verbindungen als Oxydationsäquivalente entstehenden Carbonium-Oxonium-fluoroborate in guten Ausbeuten isoliert werden. Tertiäre Amine reduzieren die Diazonium-fluoroborate in Acetonitril-Lö-sung zu den entspr. ArH-Verbindungen unter Übertragung eines a-ständigen Hydrid-Ions und Bildung von Carbonium-lmmonium-fluoroboraten. Einleitung

Three‐Component Metal‐Free Arylation of Isocyanides

“…In addition, the triggering effect of added acetate is more in favor of a radical pathway. Single‐electron transfer (SET) between radical intermediates and diazonium salts has been classically observed in Meerwein arylation of electron‐rich alkenes13 or in the reduction of diazonium salts by THF when used as solvent 14. In our case the electron‐rich nature of the imidoyl radical probably favors the electron transfer with the starting diazonium salt over competing fragmentation to nitriles.…”

Zirconocene-Initiated Intramolecular Hydride Transfer in N-Iso­alkyl-Substituted Propargylamines

“…It is known that the α-hydrogen atom in tertiary amines is prone to hydride abstraction. 17 However the carbon-carbon double bond to be reduced usually needs to be strongly activated by adjacent electron-withdrawing substituents such as CF 3 , CN, COOR, NO 2 . 18 The evidence in favor of this mechanism is the finding that the addition of sixfold excess of LiAlH 4 to the reaction mixture led to the formation of (E)-N,N-diisopropylnon-2-en-1-amine (5) in good yield (80%) when R = n-Hex (Scheme 2).…”

Flow Hydrodediazoniation of Aromatic Heterocycles

“…A less utilised aspect is the replacement of an aromatic amine (via a diazonium) for a proton; essentially a defunctionalisation step, this can be a creative and useful sequence as the amine is a powerful directing group in more complex, multi-stage syntheses [1,2]. Historically, simple anilines that form relatively-stable diazonium salts are readily deaminated in good yields under batch conditions [3,4,5]. However, many aromatic heterocycles, such as 2-amino-pyrazoles and pyridines, do not form stable diazonium salts and hence batch procedures form the target deaminated product in generally poor yield.…”