Manganese‐Catalyzed Asymmetric Hydrogenation of Quinolines Enabled by π–π Interaction**

Abstract

The non-noble metal-catalyzed asymmetric hydrogenation of N-heteroaromatics, quinolines, is reported. A new chiral pincer manganese catalyst showed outstanding catalytic activity in the asymmetric hydrogenation of quinolines, affording high yields and enantioselectivities (up to 97 % ee). A turnover number of 3840 was reached at a low catalyst loading (S/C = 4000), which is competitive with the activity of most effective noble metal catalysts for this reaction. The precise regulation of the enantioselectivity were ensured by a p-p interaction. Scheme 1. AH of 2-substituted quinolines.

Borane-catalyzed cascade Friedel–Crafts alkylation/[1,5]-hydride transfer/Mannich cyclization to afford tetrahydroquinolines

“… 1 Due to its importance, development of efficient methods to construct the THQ skeleton has been extensively explored in organic synthesis. Various approaches have been established, including intramolecular cyclization, 2 Povarov reactions, 3 hydrogenation of quinolines 4 and others. 5 Among all the strategies, the oxidative Povarov reaction, a dehydrogenative [4 + 2] annulation reaction between N -alkylanilines and alkenes, represents a promising protocol for the construction of THQs from simple starting materials ( Scheme 1a ).…”

Simultaneous Kinetic Resolution and Asymmetric Induction within a Borrowing Hydrogen Cascade Mediated by a Single Catalyst

“…Finally,wecompared the DFT-computed transition structures (TSs)f or the chiral recognition (Figure 1A)a nd asymmetric induction (Figure 1B)t oe lucidate the origins of the experimentally observed stereochemical outcomes.T he TSs feature the hydride transfer between the substrate and the ruthenium center. There is no apparent steric clashed in these TSs.F or the chiral recognition (kinetic resolution) process (Figure 1A), one major difference for the two TSs can be observed:t he favored TS1A (R) features p-p interactions [8] between the phenyl ring of the substrate and the pyridine ring of the catalyst, while the disfavored TS1B (S) has p-p interactions between two phenyl rings,o ne from the substrate and one from the catalyst (both highlighted in green color). Thef ormer is likely to be more favorable than the latter as the metal-coordinating pyridine is electron-poor and the phenyl ring of the substrate is electron-rich.…”

The Rise of Manganese-Catalyzed Reduction Reactions

“…MLC manganese complexes have also been used to hydrogenate quinolines and N-heteroaromatic molecules: by the group of Liu (33) (vide supra), [78] then the group of Rueping with a 'type B' catalyst, [103] and finally asymmetric quinoline hydrogenation was performed by Lan and Liu. [104] Despite the use of a base and a specialized ligand system, none of the three systems had any significant improvements in temperature, H2 pressure, or time. In 2017, Beller and co-workers used complex 33 to reduce amides to amine and alcohol.…”