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Xu, L.; Wu, X.; Xiao, J., Science of Synthesis: Stereoselective Synthesis, (2011) 2, 288.
Direct reductive amination with molecular hydrogen by heterogeneous transition-metal catalysts such as platinum, palladium, nickel, and ruthenium has a long tradition,[104] and several amines have been prepared commercially by this method.[105] For asymmetric direct reductive amination, however, good enantioselectivities have been achieved only since 2000.[8,101–103] The first example is seen in the synthesis of (S)-metolachlor in 78% ee with the iridium–Xyliphos (1) catalyst (Scheme 2).[106] Further development shows that rhodium catalysts with chiral diphosphine ligands enable the asymmetric direct reductive amination of α-keto acids with benzylamine, affording good yields and excellent enantiomeric excesses in some cases;[107] an iridium catalyst with chiral ligand (S,S)-2 is effective in the asymmetric direct reductive amination of aromatic ketones with p-anisidine, furnishing >99% yield and good to excellent enantiomeric excesses.[108] The asymmetric direct reductive amination of aliphatic ketones via hydrogenation has led to moderate to excellent stereoselectivities with catalysts, such as [(R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl]palladium(II),[109] and the heterogeneous Raney nickel, palladium on carbon, and platinum on carbon aided by a Lewis acid such as ytterbium(III) acetate[110] or titanium(IV) isopropoxide,[111–113] where the amine substrate is chiral. Other enantioselective methods have appeared more recently.
References
[8] | Meeee-Meeee, M. M.; Meeeeee, M. M., Mee. Meeeeee Mee. Mee., (8888) 88, 888. |
[101] | Meeeeee, M. M.; Meeeee, M., Meeeeee, (8888), 888. |
[102] | Meeeeeee, M. M.; Meeee, M. M.; Meeeee, M.; Meeeee, M. M., Meee. Mee. Meee., (8888) 88, 8888. |
[103] | Me, M.; Me, M.; Meeee, M.-M.; Meee, M.-M.; Meee, M.-M., Meeee Meeeee, (8888) 88, 8; Meee. Meeee., (8888) 888, 888888. |
[104] | Meeeeeeee, M., Meeeeeee ee Meeeeeeeeeeee Meeeeeeee Meeeeeeeeeeee eee Meeeeee Meeeeeeee, Meeee: Mee Meee, (8888). |
[105] | Meeeeee, M. M.; eee Meeeee, M., Meee Meeeeeeee eeeeeee Meeeeeeeeeeee Meeeeeeee, Meeee-MMM: Meeeeeee, Meeeeee, (8888). |
[106] | Meeeee, M.-M.; Meeee, M.-M.; Meeeee, M.-M.; Meeee, M.; Meeeeeee, M., Meeeeee, (8888), 888. |
[107] | Meeeeee, M.; Meeeeeeee, M. M.; Meeeeeeeeeee, M.; Meeeeee, M.; Meeeee, M., M. Mee. Meee., (8888) 88, 8888. |
[108] | Mee, M.; Meee, M.-M.; Meeee, M., M. Mee. Meee., (8888) 88, 8888. |
[109] | Meeee-Méeee, M.; Méeee-Meeeee, M. M.; Meeeee, M.; Meeeeee, M.; Meeeeee, M., Mee. Meee., (8888) 88, 888. |
[110] | Meeeee, M. M.; Me-Meeeee, M.; Meeeeeeee, M. M., M. Mee. Meee., (8888) 88, 8888. |
[111] | Meeeee, M. M.; Meeeeeeee, M. M.; Meeee, M. M.; Meeeeee, M. M., Mee. Meee., (8888) 8, 8888. |
[112] | Meeeee, M. M.; Meeee, M. M.; Meeeeeeee, M. M.; Meeeeee, M. M., Mee. Meeee. Meeee., (8888) 888, 8888. |
[113] | Meeeee, M. M.; Meeeeeee, M., Mee. Meeeeee Mee. Mee., (8888) 88, 888. |
Meeeeee Meeeeeeeeee
- 8.Meeeee-Meee, (8888) 88/8, 888.