N−H Imine as a Powerful Directing Group for Cobalt‐Catalyzed Olefin Hydroarylation

Abstract

N-alkyl and N-aryl imines have been frequently used as directing groups in rhodium- and cobalt-catalyzed hydroarylation reactions of olefins and alkynes. However, the scope of such hydroarylation reactions has been limited by the difficulty of preparation of sterically hindered imines by condensation, and also by the steric bulkiness of the imine group itself. Reported herein is that an N-H imine serves as an alternative and highly effective directing group for cobalt-catalyzed hydroarylation of olefins, and unlocks many of the limitations associated with the previously employed N-aryl imine directing group. The power of this minimal nitrogen directing group is manifested in a fourfold ortho alkylation of benzophenone imine, and it occurs rapidly at ambient temperature.

Beyond Friedel and Crafts: Directed Alkylation of C−H Bonds in Arenes

“…[55] This was further extended to the branched-selective ortho-alkylation of aromatic aldimines [58] and to the enantioselective alkylation of 3iminoindoles with styrenes, [59] ar eaction that can also be performed in combination with an isomerization starting from nonconjugated alkenes [60] or, in an on-enantioselective manner,w ith simple iron catalysts. [61] Interestingly,N ÀHimines were also found to be efficient substrates for directed alkylations with alkenes [62] and the Yoshikai group reported in 2016 that the Grignard reagents required in all these procedures could be efficiently replaced by simple magnesium metal. [63] Although the use of alkenes for the alkylation of arylcarbonyl derivatives has been extensively studied, limitations still remain in terms of scope.S ome of these limitations can be addressed by using other alkylating reagents,w ith alkyl halides being especially attractive candidates:t heir use will be summarized in the following section.…”

Jenseits von Friedel und Crafts: dirigierte Alkylierung von C‐H‐Bindungen in Arenen

“…[55] Diese Methode wurde ausgeweitet auf die verzweigt-selektive ortho-Alkylierung aromatischer Aldimine [58] sowie auf die enantioselektive Alkylierung von 3-Iminoindolen mit Styrolen, [59] die auch in Kombination mit einer Isomerisierung ausgehend von nicht-konjugierten Alkenen [60] oder (nicht enantioselektiv) mit einfachen Eisenkatalysatoren ausgeführt werden kann. [61] Interessanterweise erwiesen sich N-H-Imine ebenfalls als effiziente Substrate fürd ie dirigierte Alkylierung mit Alke-nen, [62] und die Gruppe von Yoshikai berichtete 2016, dass sich die in all diesen Verfahren erforderlichen Grignard-Reagentien effizient durch einfaches Magnesiummetall ersetzen ließen. [63] Obwohl die Umsetzung von Alkenen fürdie Alkylierung von Arylcarbonylderivaten ausführlich untersucht wurde, bestehen noch immer Einschränkungen hinsichtlich der Anwendungsbreite.Einige davon kçnnen durch die Verwendung anderer Alkylierungereagentienu mgangen werden, wobei Alkylhalogenide besonders vielversprechende Kandidaten sind.…”

Linear Selective C–H Bond Alkylation with Activated Olefins Catalyzed by Cp*CoIII

“…[7b] Several metal catalysts have been employed for the above reactions . In this regard, Matsunaga[9a] and others recently reported the oxidative coupling of activated olefins to obtain Mizoroki–Heck products by using a Cp*Co III (Cp* = pentamethylcyclopentadienyl) catalyst (Scheme a) , . Ellman reported a three‐component approach for a cascade addition with activated olefins and aldehydes by using Cp*Co III under redox‐neutral conditions (Scheme b) .…”