Asymmetric Hydrogenation of Quinolines Catalyzed by Iridium Complexes of Monodentate BINOL-Derived Phosphoramidites

Iridium-Catalyzed Asymmetric Transfer Hydrogenation of Quinolines in Biphasic Systems or Water

An asymmetric transfer hydrogenation (ATH) of quinolines in water or biphasic systems was developed. This ATH reaction proceeds smoothly without the need for inert atmosphere protection in the presence of a water-soluble iridium catalyst, which bears an easily available aminobenzimidazole ligand. This ATH system can work at a catalyst loading of 0.001 mol % (S/C = 100 000, turnover number (TON) of up to 33 000) under mild reaction conditions. The turnover frequency (TOF) value can reach as high as 90 000 h-1. A variety of quinoline and N-heteroaryl compounds are transformed into the desired products in high yield and up to 99% enantiomeric excess (ee).

Highly Diastereo- and Enantioselective Ir-Catalyzed Hydrogenation of 2,3-Disubstituted Quinolines with Structurally Fine-Tuned Phosphine-Phosphoramidite Ligands

A highly diastereo- and enantioselective Ir-catalyzed hydrogenation of unfunctionalized 2,3-disubstituted quinolines, especially 3-alkyl-2-arylquinolines, has been realized. The success of this hydrogenation is ascribed to the use of a structurally fine-tuned chiral phosphine-phosphoramidite ligand with a (S_a)-3,3'-dimethyl H₈-naphthyl moiety and (R_c)-1-phenylethylamine backbone. The hydrogenation displayed broad functional group tolerance, thus furnishing a wide range of optically active 2,3-disubstituted tetrahydroquinolines in up to 96% ee and with perfect cis-diastereoselectivity.

Highly Enantioselective Catalytic Addition of Grignard Reagents to N-Heterocyclic Acceptors

General methods to prepare chiral N‐heterocyclic molecular scaffolds are greatly sought after because of their significance in medicinal chemistry. Described here is the first general catalytic methodology to access a wide variety of chiral 2‐ and 4‐substituted tetrahydro‐quinolones, dihydro‐4‐pyridones, and piperidones with excellent yields and enantioselectivities, utilizing a single catalyst system.

Selective Arene Hydrogenation for Direct Access to Saturated Carbo- and Heterocycles

Arene hydrogenation provides direct access to saturated carbo- and heterocycles and thus its strategic application may be used to shorten synthetic routes. This powerful transformation is widely applied in industry and is expected to facilitate major breakthroughs in the applied sciences. The ability to overcome aromaticity while controlling diastereo-, enantio-, and chemoselectivity is central to the use of hydrogenation in the preparation of complex molecules. In general, the hydrogenation of multisubstituted arenes yields predominantly the cis isomer. Enantiocontrol is imparted by chiral auxiliaries, Brønsted acids, or transition-metal catalysts. Recent studies have demonstrated that highly chemoselective transformations are possible. Such methods and the underlying strategies are reviewed herein, with an emphasis on synthetically useful examples that employ readily available catalysts.

Pd nanoparticles on green support as dip-catalyst: a facile transfer hydrogenation of olefins and N-heteroarenes in water

Chemo- and regioselective hydrogenation methods using highly green sources, particularly from metal nanoparticles on plant stem as support and water, is an intensive research area, which is highly relevant to the development of green chemistry and technology in the 21^st century. Here, the synthesis and activity of a heterogeneous catalytic system (called “dip-catalyst”) for the transfer hydrogenation of a series of styrenyl, unfunctionalized olefins, quinoline and other N-heteroarenes, are presented. It consists of Pd nanoparticles (15–20 nm) anchored on bio-processed jute plant (Corchorus genus) stem as the support. Pd nanoparticles were decorated on the green support (GS) jute stem by the in situ reduction of K₂PdCl₄ in aqueous medium at 70 °C, using formic acid as the reductant. The Pd@GS was characterized using SEM, EDS, XRD, FTIR, XPS and TEM. Elemental mapping revealed uniform distribution of Pd on the cellulose matrix of the jute stem. The catalyst was successfully applied to the chemoselective transfer hydrogenation of numerous styrenyl, unfunctionalized olefins. Its high functional group tolerance was investigated during the olefins hydrogenation in water. Furthermore, Pd@GS was capable of quantitative hydrogenation to selectively produce 1,2,3,4-tetrahydroquinoline (THQ) in water using stoichiometric amounts of tetrahydroxydiboron (THDB) at 60 °C with turn over frequency (TOF) 4938 h⁻¹. This system is stable in water and displays excellent recyclability; it could be used for 32 consecutive cycles, without losing its original crystallinity or requiring replenishment.

A dip catalyst consisting of Pd nanoparticles immobilized on the surface of thin slices of jute-stem was fabricated. Its versatility as a hydrogen transfer agent for styrenyl, cyclic and unfunctionalized olefins and N-heterocycles was investigated.

Facile hydrogenation of N-heteroarenes by magnetic nanoparticle-supported sub-nanometric Rh catalysts in aqueous medium

This work describes the preparation and systematic characterization of a reusable magnetic heterogeneous nanocatalyst (Rh@Fe₃O₄) for the hydrogenation of N-heterocycles and simple aromatics.

Enantioselective Synthesis of Tetrahydroquinolines by Borrowing Hydrogen Methodology: Cooperative Catalysis by an Achiral Iridacycle and a Chiral Phosphoric Acid

We report herein the highly enantioselective synthesis of 2-substituted tetrahydroquinolines through borrowing hydrogen, a process recognized for its environmentally benign and atom-economical nature. The use of an achiral iridacycle complex in combination with a chiral phosphoric acid as catalysts was the key to the development of this highly efficient and enantioselective transformation.

Selective Catalytic Hydrogenation of Heteroarenes with N-Graphene-Modified Cobalt Nanoparticles (Co3O4-Co/NGr@α-Al2O3)

Cobalt oxide/cobalt-based nanoparticles featuring a core-shell structure and nitrogen-doped graphene layers on alumina are obtained by pyrolysis of Co(OAc)2/phenanthroline. The resulting core-shell material (Co3O4-Co/NGr@α-Al2O3) was successfully applied in the catalytic hydrogenation of a variety of N-heteroarenes including quinolines, acridines, benzo[h], and 1,5-naphthyridine as well as unprotected indoles. The peculiar structure of the novel heterogeneous catalyst enables activation of molecular hydrogen at comparably low temperature. Both high activity and selectivity were achieved in these hydrogenation processes, to give important building blocks for bioactive compounds as well as the pharmaceutical industry.

Efficient asymmetric hydrogenation of quinolines in neat water catalyzed by chiral cationic Ru-diamine complexes

The first highly effective and enantioselective hydrogenation of quinolines catalyzed by chiral cationic Ru-diamine complexes in undegassed water was developed.

Thiourea as an efficient organocatalyst for the transfer hydrogenation of 2-substituted quinoline derivatives

This study reports on the first transfer hydrogenation of 2-substituted quinolines promoted by a thiourea catalyst with Hantzsch 1,4-dihydropyridine as the hydrogen source.