Abstract
Highly regio- and enantioselective intermolecular hydroamination of alkenes is a challenging process potentially leading to valuable chiral amines. Hydroamination of alkenes via metal-catalyzed 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 Markovnikov-type 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.
Highlights
Regio- and enantioselective intermolecular hydroamination of alkenes is a challenging process potentially leading to valuable chiral amines
Continuing our pursuit of efficient earth-abundant transition metal catalysis via ligand design[36,37,38,39,40,41,42,43,44,45]; here, we report the use of unsymmetric NNN tridentate ligands to promote the cobaltcatalyzed radical hydroamination of alkenes via hydrogen atom transfer (HAT) (Fig. 2d)
The standard conditions were identified as 0.36 mmol of alkene 1, 0.3 mmol of α-diazo ester compound 2, 5 mol% of Co(OAc)[2, 6] mol% of L4, and 1.2 equiv. of PhSiH3 in a solution of THF (0.25 M) at room temperature (r.t.) for 12 h
Summary
Regio- and enantioselective intermolecular hydroamination of alkenes is a challenging process potentially leading to valuable chiral amines. 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. Metal-catalyzed hydrofunctionalization of readily available alkenes with nitrogen sources is one of the most efficient methods for the synthesis of nitrogen-containing molecules; to achieve the high regio- and enantioselectivities of this transformation is still a challenge (Fig. 2a)[4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. The discovery of suitable ligand scaffolds for metal-catalyzed radical hydroamination of alkenes is a challenge and has great potential (Fig. 2c)
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