Asymmetric Hydrogenation of 2- and 2,3-Substituted Quinoxalines with Chiral Cationic Ruthenium Diamine Catalysts

Abstract

The enantioselective hydrogenation of 2-alkyl- and 2-aryl-subsituted quinoxalines and 2,3-disubstituted quinoxalines was developed by using the cationic Ru(η(6)-cymene)(monosulfonylated diamine)(BArF) system in high yields with up to 99% ee. The counteranion was found to be critically important for the high enantioselectivity and/or diastereoselectivity.

Catalytic sugar-assisted transfer hydrogenation with Ru(II), Rh(III) and Ir(III) halfsandwich complexes

“…Such compounds with chelating nitrogen ligands are effectively used in catalysis, e. g. in water oxidation [23], intramolecular hydroamination of alkynes [24], Diels-Alder reactions [25], asymmetric Michael addition reactions [26], asymmetric hydrogenation [27,28], and transfer hydrogenation [29][30][31], reactions of ketones and imines.…”

Additive Effects of Amines on Asymmetric Hydrogenation of Quinoxalines Catalyzed by Chiral Iridium Complexes

“…Asymmetric hydrogenation of N‐heteroaromatic compounds is considered to be a difficult task due to aromatic resonance stability. Recent developments in asymmetric hydrogenation of N‐heteroaromatic compounds,2 such as 2‐substituted quinolines3–15 and quinoxalines3h, k, 4c, f, 11, 16–22 (to give the 1,2,3,4‐tetrahydroquinoline and 1,2,3,4‐tetrahydroquinoxaline derivatives, respectively, in high enantioselectivity), pyridine derivatives,3h, 4g, 23 pyrroles,24 imidazole,25 oxazole,25 and indoles,26 have been remarkable. However, only a few mechanistic studies of the asymmetric hydrogenation of N‐heteroaromatics have been reported.…”

Highly Enantioselective Synthesis of Indolines: Asymmetric Hydrogenation at Ambient Temperature and Pressure with Cationic Ruthenium Diamine Catalysts

“…2-Alkyl-substituted indoles were hydrogenated in very good yields with excellent enantioselectivities (entries 1-11), regardless of either the length of side chain or the position of substituents at the phenyl ring. Notably,e xcellent results were also achieved with 2,3-disubstituted fused ring indolines (entries [12][13][14][15][16]. It was found that the enantiomeric excess increased from 89 to 99 %when increasing the ring size from five-to six-and seven-membered rings.I na ddition, the hydrogenation of 2,3-dimethylindole could be carried out under harsh reaction conditions (entry 17).…”