Ligand-promoted cobalt-catalyzed radical hydroamination of alkenes

Abstract

Highly regio-and enantioselective intermolecular hydroamination of alkenes is a challenging process potentially leading to valuable chiral amines. Hydroamination of alkenes via metalcatalyzed hydrogen atom transfer (HAT) with good regioselectivity and functional group tolerance has been reported, however, high enantioselectivity has not been achieved due to the lack of suitable ligands. Here we report a ligand-promoted cobalt-catalyzed Markovnikovtype selective radical hydroamination of alkenes with diazo compounds. This operationally simple protocol uses unsymmetric NNN-tridentate (UNT) ligand, readily available alkenes and hydrosilanes to construct hydrazones with good functional group tolerance. The hydrazones can undergo nitrogen-nitrogen bond cleavage smoothly to deliver valuable amine derivatives. Additionally, asymmetric intermolecular hydroamination of unactivated aliphatic terminal alkenes using chiral N-imidazolinylphenyl 8-aminoquinoline (IPAQ) ligands has also been achieved to afford chiral amine derivatives with good enantioselectivities.

Catalytic hydrogen atom transfer to alkenes: a roadmap for metal hydrides and radicals

“…It should be noted that an intermolecular asymmetric Markovnikov hydroamination of alkenes from electronically unbiased alkenes and donor-acceptor diazo reagents (77-84% ee) could potentially proceed via a MHAT mechanism as well. 141 In this case, a newly developed N-imidazolinylphenyl 8-aminoquinoline ligand was used. A detailed exploration of the enantiodetermining step is not included in this report, although the presence of radicals was implicated by cyclopropyl ring opening.…”

Iron and cobalt catalysis: new perspectives in synthetic radical chemistry

“…93:7) in good yields using the cobalt(III)-catalysed alkene hydroamination methodology via HAT. 157 The optimal asymmetric induction was provided by using 6 mol% of a chiral NNN-tridentate ligand, the Nimidazolinylphenyl 8-aminoquinoline (IPAQ) ligand.…”

Dual Cobalt and Photoredox Catalysis Enabled Redox‐Neutral Annulation of 2‐Propynolphenols

“…The radical could either escape from the cage and thus be captured by radicalophiles [2] or recombine with metal to form the cage‐collapsed organometallics complex which would undergo transmetalation with other metals and thus introducing new functionalities [3] . Catalysts based on cobalt are among the most studied systems for these types of transformations and proved extremely versatile (Scheme 1a, I and II) [2a–l] . Recently, Shigehisa, [4] Pronin, [5] and Zhu [6] suggested that the radical or collapsed alkylcobalt(III) intermediate could be further transformed into a carbocation or alkylcobalt(IV) species via single electron oxidation process in the presence of N ‐fluorocollidinium salt or excited photocatalyst, and which can be captured by nucleophiles (Scheme 1a, III).…”