Efficient Asymmetric Hydrogenation of Quinolines over Chiral Porous Polymers Integrated with Substrate Activation Sites

Abstract

Heterogeneous asymmetric hydrogenation of quinolines for the production of optically active tetrahydroquinoline derivatives still remains a difficult task due to the aromatic stability of quinolines. Herein, we reported efficient heterogeneous asymmetric hydrogenation of quinolines over chiral porous polymers integrated with both chiral active sites (VDPEN-RuOTs) and substrate activation sites (TsOH). The porous polymer integrated with TsOH is 10 times more active than that without TsOH in the asymmetric hydrogenation of 2-methylquinoline. The volcano curve of TOF with the TsOH/Ru ratio confirms the synergistic catalysis of VDPEN-RuOTs and TsOH. Comparison results with a homogeneous catalytic system imply that the synergy between chiral centers and acidic sites is greatly enhanced in the polymer network. Under optimized conditions, the chiral porous polymer afforded up to 90% ee with 90 h −1 TOF, which is one of the best solid catalysts for asymmetric hydrogenation of quinoline derivatives ever reported. Furthermore, the bifunctional porous polymers realized the asymmetric cascade hydrogenation/reductive amination reaction to obtain benzo-quinolizidines. Our primary results suggest that the incorporation of substrate activation sites near chiral centers is an efficient strategy for the synthesis of high-performance solid catalysts for heterogeneous asymmetric catalysis.

Synthesis of Sulfonated Porous Organic Polymers with a Hydrophobic Core for Efficient Acidic Catalysis in Organic Transformations

“…FT‐IR spectra of all the sulfonated polymers show a strong vibration at 2922 cm −1 , which could be assigned to the C−H bond formed during the free radical polymerization of the vinyl‐functionalized monomers. The incorporation of the SO 3 H groups in the polymer networks was confirmed by the peak at 560 cm −1 attributed to C−S stretching, and two strong vibrations at 1040 and 1165 cm −1 , characteristic of the asymmetric and symmetric stretching of O=S=O, respectively [42,43] . 13 C CP‐MAS NMR spectroscopy was also employed to characterize S‐PT‐24 as a representative sample.…”

Development of efficient solid chiral catalysts with designable linkage for asymmetric transfer hydrogenation of quinoline derivatives

“…Using SBA-ILBF4-TsDPEN50 as a representative sample, the characteristic peaks for C=C vibrations of the phenyl ring at ~1450-1550 cm -1 and the S=O stretching peak at 1157 cm - 13 C NMR spectrum of imidazole-TsDPEN-N-Boc in CDCl3; (d) 13 C CP/TOSS NMR spectrum of SBA-ILBF4-TsDPEN50. [27][28][29], demonstrating the successful incorporation of the chiral ligands with IL linkages into SBA-15 by this one-pot method. In comparison with imidazole-TsDPEN-N-Boc, the characteristic peak of the C=O stretching vibration at 1710 cm -1 shifted slightly to 1700 cm -1 for SBA-ILBr-TsDPENx-N-Boc (Fig.…”

Recent advances in the asymmetric reduction of imines by recycled catalyst systems

“…16 Recently, Yang and co-workers proposed bi-functional chiral porous polymers, containing chiral Ru-DPEN center and strong acid site aiming at substrate activation, which might address this issue of low activities. 17 These bifunctional polymers were readily available according to a modified literature method. Scheme 8 shows the synthetic route, where x represents the molar ratio of acidic sites relative to chiral active sites.…”