Cobalt-catalysed site-selective intra- and intermolecular dehydrogenative amination of unactivated sp3 carbons

Abstract

Cobalt-catalysed sp2 C–H bond functionalization has attracted considerable attention in recent years because of the low cost of cobalt complexes and interesting modes of action in the process. In comparison, much less efforts have been devoted to the sp3 carbons. Here we report the cobalt-catalysed site-selective dehydrogenative cyclization of aliphatic amides via a C–H bond functionalization process on unactivated sp3 carbons with the assistance of a bidentate directing group. This method provides a straightforward synthesis of monocyclic and spiro β- or γ-lactams with good to excellent stereoselectivity and functional group tolerance. In addition, a new procedure has been developed to selectively remove the directing group, which enables the synthesis of free β- or γ-lactam compounds. Furthermore, the first cobalt-catalysed intermolecular dehydrogenative amination of unactivated sp3 carbons is also realized.

Cp*CoIII‐Catalyzed C(sp3)−H Bond Amidation of 8‐Methylquinoline

“…[15] However, the reaction requiresh ighert emperatures and stoichiometrica mounts of oxidants. Our exploration on the use of first row transition metals for CÀHb ond functionalization [16] prompted us to investigate direct amidation of C(sp 3 )ÀHb onds using Cp*Co III based catalysts.…”

Nickel, Cobalt and Palladium Catalysed C−H Functionalization of Un‐Activated C(sp3)−H Bond

“…Oxidative cyclisation of 2‐ethyl‐2‐methyl‐N‐(quinolin‐8‐yl) pentanamide in catalytic amount of CoCl 2 by employing Ag 2 CO 3 as oxidant along with chlorobenzene as solvent produces β‐lactam in 33 % yield. Interestingly, this reaction proceeds in highly selective manner, favoring C−H bond of β‐methyl group over β‐methylene and γ‐methyl groups . Further, optimization shows that the reaction can be improved by using Co(OAc) 2 as catalyst, afterwards decreasing the loading of base significantly improved the chemical yield of product.…”

Komplementäre Strategien für die dirigierte C(sp3)‐H‐Funktionalisierung: ein Vergleich von übergangsmetallkatalysierter Aktivierung, Wasserstoffatomtransfer und Carben‐ oder Nitrentransfer

“…Li und Ge zeigten, dass das Amid 203 in Abwesenheit eines Alkins unter ähnlichen Reaktionsbedingungen eine b-Lactamisierung unter Bildung des b-Lactams 204 durchläuft. [103] Eine inter- [104] und Gaunt [105] stellten unabhängig voneinander fest, dass Co(acac) 2 [108] Nach dem postulierten Mechanismus bindet ein Nitronatligand über einen Ligandenaustausch an das Kupfer-(III)-alkyl H1,w odurch das Zwischenprodukt H2 entsteht. Eine reduktive Eliminierung führt zur Bildung einer C-CBindung und des Intermediats 210,d as weiter in das beobachtete cyclisierte Produkt 196 umgewandelt wird.…”